Comparing the growth and weight relationships of the Arctic toothed whales (Monodontidae)

This update on the small cetacean body mass database describes what I’ve accumulated for the narwhal (Monodon monoceros) and the beluga (Delphinapterus leucas). Like my previous posts on river dolphins and kogiids, I will also provide some insights into my methods of data collection and discussion the nature of some of the information I’ve collected.

The Horned and the White Whales

Both the beluga and narwhal are medium-sized toothed whales that live along the Arctic and subarctic waters. Belugas possess a circumpolar distribution whereas the narwhal is only native to the Northern Europe and Eastern Canada, with few vagrants observed off Alaska. The first scientific description of the beluga came from observations of harvests along the Ob river and was assigned the name Delphinus leucas (Pallas, 1776), meaning “white dolphin’’. The current generic name, Delphinapterus (La Cépède, 1804), refers to the absence of the dorsal fin. Having been formally described in Russia, the common name is derived from the word for ‘’white’’.

Before being formally described, the narwhal’s tusk was well known from its association with the Biblical unicorn (Bartholin, 1678; Pluskowski, 2004; Tomilin, 1967; Worm, 1655). The narwhal was also among the first whales described in System Naturae (Linnaeus, 1758). The tusk is referenced in both the generic (“One tooth’’) and specific names (“one horn’’). The common name is thought to have come from the Old Norse term meaning ‘’corpse whale’’ (Mansfield et al., 1975), in reference to the mottled skin resembling a decayed appearance.

While early taxonomic schemes classified narwhals and belugas within the Delphinidae family along with oceanic dolphins (Kleinenberg et al., 1969), they have since been separated into their own family, Monodontidae. Fossil species firmly classified into this family such as Bohaskaia monodontoides in the Northwest Atlantic (Vélez-Juarbe & Pyenson, 2012), Haborodelphis japonicus in the Northwest Pacific (Ichishima et al., 2019) and Casatia thermophila from the Mediterranean (Bianucci et al., 2019; Merella et al., 2022) were from the early Pliocene. The latter supports that Monodontids evolved in more temperature waters prior to cooling evens (Bianucci et al., 2019). The oldest, Denebola brachycephala, from the late Miocene (~11-5.4 million years ago) was found in the Eastern North Pacific (Barnes, 1984).

The unfused cervical vertebrae distinguishes extant Monodontidae from all other cetaceans. This feature, along with others, supports that Odobenocetops is related to monodontids (de Muizon, 1993; de Muizon et al., 1999; de Muizon & Domning, 2002). Molecular studies indicate that monodontids are the nearest extant relatives to porpoises (Phocoenidae). While narwhals and belugas are classified into separate genera, hybridization has been confirmed (Heide‐Jørgensen & Reeves, 1993; Skovrind et al., 2019).

Indigenous populations along North America, Russia, and Greenland all have long histories of harvesting both species (Hay, 1984; Kleinenberg et al., 1969), which is currently regulated by each nation’s government (Gonzalez, 2001; Heide-Jørgensen et al., 2010; Huntington & The Communities of Buckland, 1999; Shpak et al., 2020; Tyrrell, 2008) rather than the IWC. It is from these harvests that we obtain much of our recent data on these species (Garde et al., 2007; Hansen et al., 1990; Suydam, 2009).

While narwhals have rarely ever been held in captivity, belugas were the species to first, with P.T. Barnum being one of the earliest proprietors (Ceta-Base: Online Marine Mammal Inventory, 2010).

Life History and Growth

Tables 1 & 2 compares the size parameters for different populations of both species. Belugas are known to change in pigment with age. They’re an off-black color at birth and progressively become whiter towards adulthood (Kleinenberg et al., 1969). This was a useful, but imprecise indicator of age for the earliest examinations into this species’ life history. The transition towards a full-white pigment appears to closely coincide with sexual maturity in males, but females typically mature before becoming fully white (Kleinenberg et al., 1969).

Age estimations in both species are conventionally calculated using laminations from growth layers in the teeth (Mansfield et al., 1975; Sergeant & Brodie, 1969). In the case of the narwhal, this is done with the embedded incisor opposite of the tusk. There’s some debates as whether 1 or 2 layers form per year for the beluga (Luque & Ferguson, 2010; Sergeant, 1973), however I’m leaning towards the 2 layer/year conversion based on validation from captive individuals of known age (Brodie & Haulena, 2018). By this standard, belugas around the world appear become sexually mature at consistent ages of around 5 and 7-9 years for males and females respectively (Brodie, 1971; Kleinenberg et al., 1969; Sergeant, 1973; Suydam, 2009). Physical maturity generally appears to occur between 10-20 years of age.

Use of another technique called aspartic acid racemization (AAR), an aging technique applied to the eye lens (Garde et al., 2007), suggests narwhals also exhibit biannual deposition rate for growth layers. The maximum ages I could find for both species appears to exceed 50 years for belugas (Sergeant, 1973) and 107.7 years for narwhals (Garde et al., 2022).

Table 1 : Size parameters for D. leucas

Region	L_b (cm)	L_sm(cm) M/F	L_∞(cm) M/F	L_max M/F	Source
W. Hudson Bay	151	310 / 290	377 / 328	448 / 400	(Doan & Douglas, 1953; Doidge, 1990b; Sergeant, 1973)
E. Hudson Bay		316 / 280^a	349 / 330	440^b / 400^b	(Doidge, 1990b, 1990a)
Cumberland Sound	160	378^c / 308	427 / 362	450^b / 400^b	(Brodie, 1971; Luque & Ferguson, 2010)
White & Kara Seas	160	380^d / 350	438 / 378	479 / 420	(Heide-Jørgensen & Teilmann, 1994; Kleinenberg et al., 1969; Ognetov, 2007)
Alaska	155	369^e / 289	432^f / 370^f	485 / 410	(Burns & Seaman, 1986; Suydam, 2009)
St. Lawrence Estuary	160	381^g / 336^g	416 / 365	456 / 409	(Lair et al., 2015; Lesage et al., 2014; Vladykov, 1944)
W. Greenland	155^a	390 / 345	483 / 386	545 / 482	(Degerbøl & Nielsen, 1930; Heide-Jørgensen & Teilmann, 1994)
Okhotsk Sea	170	390^h / 343ⁱ	—^j / 390	590^a / 490^a	(Dorofeev & Klumov, 1936; Kleinenberg et al., 1969)

a. Mean of listed range or binned value
b. Approximation from figure.
c. Estimation from Gompertz curve from Luque & Ferguson, 2010 at age 7
d. Approximation from Ognetov, 2007’s age-length key for age 8
e. Average of Eastern Chukchi and Cook Inlet Males at 7 years (Suydam, 2009).
f. Average of multiple regions across Alaska (Suydam, 2009).
g. Estimation from growth curve from Lesage et al., 2014.
h. Based on approximate mean length from transition from grey to white (Dorofeev & Klumov, 1936).
i. Mean of smallest mature female and largest maturing female (Kleinenberg et al., 1969).
j. Insufficient data, likely > 470 cm based on modal length of white males (Dorofeev & Klumov, 1936).

Belugas are evidently a polymorphic species with respect to adult size. The Hudson Bay populations are the smallest, West Greenland and Okhotsk Sea belugas are the largest, and all other regions being intermediate. The largest belugas to be reliably documented were three females with binned lengths of 480-499 cm and two males 580-599 cm from the Okhotsk Sea (Dorofeev & Klumov, 1936).

Table 2: Size parameters for M. monoceros

Region	L_b (cm)	L_sm(cm) M/F	L_∞(cm) M/F	L_max M/F	Source
Baffin Island	161	395 / 340	470 / 415	470 / 415	(Hay, 1984; Hay & Mansfield, 1989; Mansfield et al., 1975)
W. Greenland			456 / 399	560 / 490	(Garde et al., 2015)
E. Greenland			462 / 405	480 / 441	(Garde et al., 2015)
SE. Greenland^a			463 / 406	501 / 441	(Garde et al., 2022)

a. Data includes some individuals with East Greenland Sample from Garde et al., 2015

By contrast, the adult size of narwhals appears more consistent between Eastern Canada and Greenland. A 560 cm male and 490 cm female (Garde et al., 2015) gives credence to early literature assigning maximum lengths of 600 cm for males and 500 cm for females (Tomilin, 1967). The typical size of narwhals corresponds to that of the larger-sized beluga populations. The tusk of males narwhals typically grows to 160-200 cm (Garde et al., 2015, 2022). Eighteenth century catch logs documents lengths of 267 cm (Mitchell & Reeves, 1981) and one manuscript states that the narwhal’s tusk reach 315 cm (Bruemmer, 1971). I was not able to obtain the latter source to verify the context of this measurement for myself. Excluding both of these, there are at least two verified records of tusks reaching 240 cm (Beasley, 1904; Garde et al., 2015).

Body weight

Figures 1 and 2 below are the plots for the weight data I’ve accumulated for the beluga (n= 347) and narwhal (n = 96), respectively. Nearly all were from literature as only a measly single individual was included from the USNM database. I elaborate on the heaviest individuals while describing the Okhotsk Sea material (Govorkov, 1934), but for now I’ll say the heaviest masses recorded outside of this region for each sex was a 465 cm male from the Kara Sea that weighed 1,480 kg (Ognetov, 2007) and a 388 cm female from St. Lawrence that weighed 1,003 kg (Lair et al., 2015). The corresponding records for narwhals were a 470 cm / 1,789 kg male and a 410 cm / 1,148 kg female from West Greenland (Garde et al., 2007).

Figure 1: Weight data for D. leucas

In the regional breakdown for belugas, the St. Lawerence region was by far the most numerous (n = 205), with the next two most common regions being the Hudson Bay (n = 45) and those from the White, Kara, and Barents Seas (n = 40). I even had a small sample of captive individuals (n=10), which includes one large male that weighed 1,200 kg (Brodie et al., 2013). The dataset covers nearly all the major regions except for Alaska and West Greenland. For narwhals, it was an even split between Baffin Island (n = 46) and Greenland (n = 50).

Figure 2: Weight data for M. monoceros

The narwhal dataset excludes four underweight outliers, two of which were from strandings. The weights of 16 eviscerate belugas from the West Hudson Bay were excluded (Doan & Douglas, 1953), as a previous study (Doidge, 1990b) has shown that incorrect assumptions on correction factors confound apparent differences in weight relationships (Sergeant & Brodie, 1969). An incomplete weighing for a 1,000+ kg female was also excluded (Doidge, 1990b).

Validating Govorkov’s data

My biggest goal when compiling the data was to find a decent sample from the Okhotsk Sea. Unfortunately, it appears nearly all collection of such material was restricted to obscure Soviet research from the early-mid 20^th century (Kleinenberg et al., 1969). There are currently some sources I have not been able to access (Arsenʹev, 1935, 1939), but was mentioned in other literature (Heptner et al., 1988; Kleinenberg et al., 1969; Tomilin, 1967; Vladykov, 1944). I was fortunately able to find one source (Govorkov, 1934), however this has been flagged as potentially unreliable by other authors (Kleinenberg et al., 1969; Tomilin, 1967) as it reports males as large as 667 cm and females reaching 651 cm. Figure 3 shows the diagram of the measuring procedure Govorkov presents.

Figure 3: Reported measuring scheme from Govorkov, 1934

Two things immediately struck my attention upon reviewing the source myself. First, was that the total length, as presented in the diagram, was intended to be the zoological standard. The other was that the 667 cm male and 651 cm female were the only two that exceeded 600 cm. I wouldn’t expect such a discontinuity of over 0.5 m for the next largest whales if the entire sample was equally biased. Since fluke widths, a less ambiguous measurement, was also recorded for each whale. This allowed for comparisons with other samples to validate the reliability of total lengths (Figure 4) as performed in other studies (Doidge, 1990b; Heide-Jørgensen & Teilmann, 1994). Due to the likelihood of morphological differences between geographically distant populations, I restrict my analysis to measurements taken from 31 belugas from the Amur Estuary and Yenisei Bay in the Far East (Arsenʹev, 1936; Drukker & Gakichko, 1936), as they were the nearest population. Due to size differences between the samples, I only compared Okhotsk belugas as large as 410 cm.

Figure 4: Fluke width comparisons between Okhotsk Sea with Far East Belugas

AIC model selection slightly preferred pooling the two samples (weight = 0.61) and it can be seen graphically in Figure 4 that there’s no obvious difference between the sources. It seems that the length measurements for belugas up to 410 cm showed no obvious signs of biased length measurements. Table 3 compares Govorkov’s sample against regression predictions for TL from a large sample of belugas sampled in the Eastern Chukchi sea (Suydam, 2009) and West Greenland (Heide-Jørgensen & Teilmann, 1994), TL’s for males appear accurate up to 576 cm, excluding only the 667 cm male. Meanwhile, TLs for females appears becomes uncertain past 410 cm. I suspect females with estimated TLs exceeding 500 cm may potentially have been misidentified males. Table 3 lists individuals in descending order of length and boundaries of reliability are highlighted.

Table 3: Fluke width and estimated TL from Govorkov, 1934

Sex	Total length (cm)	Fluke span (cm)	Mass (kg)	Estimated TL-Suydam	Estimated TL-Heide-Jorgensen & Teillman, 1994
F	651	157	1823	643.88	661.2173913
F	584	125	1213	586.4	522.0869565
F	561	132	1728	621.4	552.5217391
F	524	112	1493	521.4	465.5652174
F	490	98	1096	451.4	404.6956522
F	454	90	946	411.4	369.9130435
F	410	88	873	401.4	361.2173913
F	401^a	66	1312	291.4	265.5652174
F	350	76	848	341.4	309.0434783
F	320	75	720	336.4	304.6956522
F	315	66	670	291.4	265.5652174
F	304	48	720	201.4	187.3043478
F	300	63	488	276.4	252.5217391
F	230	48	248	201.4	187.3043478
F	226	46	224	191.4	178.6086957
F	198	44	215	181.4	169.9130435
M	667	136	1412	559.88	569.9130435
M	576	151	1956	619.88	635.1304348
M	536	129	1632	531.88	539.4782609
M	463	97	1437	403.88	400.3478261
M	448	104	1347	431.88	430.7826087
M	440	70	1593	295.88	282.9565217
M	401	102	816	423.88	422.0869565
M	399	79	926	331.88	322.0869565
M	375	74	742	311.88	300.3478261
M	362	78	875	327.88	317.7391304
M	225	45	448	195.88	174.2608696
M	190	45	202	195.88	174.2608696
M	170	39	194	171.88	148.173913
M	153	38	160	167.88	143.826087

a. While much larger than estimated TL, the corresponding weight suggests that the reported TL is accurate, and this female is simply at the extreme end of proportions.

While fluke measurements provided promising inferences, I didn’t stop my assessment there, as I also employed a mass-prediction model to validate the length measurements against their weight data. The text explains that girth measurements along the dorsal side were taken (probably only 60-80% of the full girth). Total length and maximum girth can potentially describe nearly all the variation in weight in small cetaceans (Garde et al., 2022; Lockyer, 1993). Therefore, overestimation in total length or girth can be detected if the estimated mass greatly exceeds the reported mass. Since Govorkov’s sample records partial girths, we should expect the estimated masses to lie consistently below the reported mass.

Table 4: Real and estimated masses from Govorkov, 1934

Sex	Length (cm)	Partial girth (cm)	Mass (kg)	Estimated mass (kg)
F	651	184	1823	2238.212919
F	584	237	1213	2136.088562
F	561	260	1728	2097.900223
F	524	238	1493	1694.167622
F	490	210	1096	1334.466323
F	454	180	946	1008.317498
F	410	170	873	774.7451589
F	401	135	1312	621.8051084
F	350	204	848	629.8911237
F	320	168	720	448.8339329
F	315	201	670	495.8081532
F	304	178	720	419.3027936
F	300	165	488	385.0483043
F	230	162	248	213.5592729
F	226	156	224	199.8901635
F	198	115	215^a	119.5678005
M	667	367	1412	3946.653259
M	576	270	1956^b	2284.723283
M	536	156	1632	1298.7888
M	463	196	1437	1121.076193
M	448	226	1347	1160.751219
M	440	196	1593	1003.882937
M	401	190	816	802.1795509
M	399	178	926	755.873231
M	375	176	742	655.2530046
M	362	234	875	750.5864558
M	225	155	448^a,c	197.0318359
M	190	116	202^a	110.0530961
M	170	113	194^a	84.80956762
M	153	94	160^a	58.84386526

a. All weights are twice as much as expected. This pattern is only seen in young animals, suggesting these were measured using different equipment that measured weight in lbs. as in Vladykov, 1944.
b. Given the consistency with fluke width, the girth was likely overestimated rather than TL.
c. Female of near-exact same dimensions weighed half as much. Converting to kg removes any difference.

A previously published mass prediction model that uses the girth near the umbilicus (Doidge, 1990b) is not appropriate for such a comparison, as the girths reported by Govorkov were at the axilla, as taken in larger whales (George, 2009; Rice & Wolman, 1971; Víkingsson et al., 1988). Therefore, I fitted my own model using a sample of 12 belugas from other data that measured the axillary girth (Drukker & Gakichko, 1936; Vladykov, 1944). This model had a notably higher correlation (r²= 0.991) than other models for belugas and narwhals that used umbilical girths (Doidge, 1990b; Garde et al., 2022).

0.00003672 (Length in cm)^2.167(Girth in cm)^0.745³

Remarkably, Table 4 shows that overestimation in mass coincides almost exactly where we see a loss in consistency in TL estimation from fluke width regressions in both sexes. Furthermore, there’s compelling evidence of a unit conversion error for most of the small individuals (< 230 cm). Since this is only observed in calves, they were likely measured using a separate set of equipment that measured in lbs. that weren’t converted to kilograms. Dividing these values by 2.2 removes this discrepancy.

It appears clear to me now that Govorkov’s data was likely pooled by different direct sources or was collected under variable conditions that impacted reliability. Cross-referencing Tables 3 & 4 supports that 23 of the TL measurements were reliable, with a 576 cm male weighing 1,956 kg and a 401 cm female weighing 1,312 kg being the heaviest records for the species.

The 651 cm female was excluded altogether, despite estimated TLs being consistent with its reported length, as it’s such an extreme outlier, even if sex was misidentified. A female reported as 454 cm and 946 kg was a bit of a judgement call, but opted to slightly downsize the length using the fluke width regression for females from the Eastern Chukchi Sea (Suydam, 2009). As for the remaining five, I chose to downsize their lengths using the unisex formula from the West Greenland population (Heide-Jørgensen & Teilmann, 1994) as it seemed better suited for both large specimens and those of uncertain sex.

Figure 1 shows that all individuals exceeding 500 cm appear proportionately lean, this seems consistent with a 520 cm beluga reported to weigh 1,372 kg (Mikhalev, 2019). It’s likely that exceptionally long individuals are leaner than those that are only slightly above average.

Weight relationships.

When looking closely at the logarithmic plots in Figures 1 & 2, there are some discontinuities to the linear pattern between juveniles and the largest individuals, causing the overall trend to appear wavy. This is particularly clear in the narwhal data. The discontinuity for individuals below 290 cm was observed for the weight data from the St. Lawrence area population (Larrat & Lair, 2022). This roughly corresponds with existing data on the size of weaning at about 230-280 cm (Kleinenberg et al., 1969; Sergeant, 1973; Suydam, 2009) and appears to apply to narwhals as well. The discontinuity for large individuals appears to be due to the accumulation of blubber in older males after their growth ceases (Hay, 1984). This pattern was also observed in other species in my database, including the 700 kg kogiids noted in my last post.

Not accounting for at least the discontinuity between juveniles and maturing individuals will confound AIC model comparisons. After separating the datasets for both species into two size classes (above 290 cm and below 290 cm), AIC model selection revealed that the narwhal’s weight relationship exhibited notable sexual differences (delta AIC > 2) and weak regional differences while the opposite was found for belugas. Both patterns were more pronounced for individuals > 290 cm. Table 5 provides a list of linear regression parameters obtained from the current dataset and those obtained from literature. All belugas exceeding 500 cm were excluded from regressions for adult-sized individuals.

Table 5: Power function parameters for Monodontidae

Species	Sex	Region	a^*	b	r²	N	Source
M. monoceros	all	Baffin Island	29.52	2.48038		41	Hay, 1984
M. monoceros	Male	Pooled	29.26	2.557	0.965	24	Current post
M. monoceros	Female	Pooled	32.3	2.403	0.978	71	Current post
D. leucas^a	Both	Hudson Bay	16.87	2.536		16	Sergeant & Brodie, 1969
D. leucas	Both	St. Lawrence	25.29	2.605		10	Sergeant & Brodie, 1969
D. leucas	Both	Hudson Bay	20.89	2.58	0.92	36	Doidge, 1990 a & b
D. leucas	Male	W. Greenland	25.69	2.47		41	Heide-Jorgensen & Tillman, 1994
D. leucas	Female	W. Greenland	35.98	2.21		57	Heide-Jorgensen & Tillman, 1994
D. leucas	Both	W. Greenland	28.25	2.37		98	Heide-Jorgensen & Tillman, 1994
D. leucas	Male	North Quebec	10.99	3.37		20	Heide-Jorgensen & Tillman, 1994
D. leucas	Female	North Quebec	40.36	2.03		16	Heide-Jorgensen & Tillman, 1994
D. leucas	Both	North Quebec	15.54	2.85		36	Heide-Jorgensen & Tillman, 1994
D. leucas	Both	Captive	40.33	2.08	0.94	9^b	Robeck et al., 2005
D. leucas	Male	Captive	40.84	2.132		5^b	Robeck et al., 2005
D. leucas	Female	Captive	47.50	2		4^b	Robeck et al., 2005
D. leucas	Both	Pooled	21.20	2.647	0.935	179	Mikhalev, 2019
D. leucas	Male	White & Kara Seas	21.38	2.6789		140	Ognetov, 2007
D. leucas	Female	White & Kara Seas	23.15	2.5668		156	Ognetov, 2007
D. leucas	Both	White & Kara Seas	21.91	2.647		296	Ognetov, 2007
D. leucas	Both	Pooled	18.74	2.773	0.959	342	Current Post
D. leucas	Both	Captive	18.70	2.781	0.970	10	Current Post
D. leucas	Both	Hudson Bay	26.43	2.413	0.896	45	Current Post
D. leucas	Both	Arctic Route	20.47	2.676	0.978	50	Current Post
D. leucas	Both	Okhotsk Sea	19.56	2.886	0.962	24	Current Post
D. leucas	Both	St. Lawrence	17.11	2.845	0.962	205	Current Post

*Constant of proportionality converted so length is in meters and mass is in kg.
a. Uses data from eviscerated whales, is very negatively biased.
b. Represents number of separate individuals; sample is derived from unspecified number of longitudinal measurements.

While AIC modeling suggests there’s a significant difference between the weight relationships between the two species, overall, there’s still decent similarity, as to be expected for close relatives (Figure 5). A general, pooled weight relationship of the total dataset is expressed below.

Mass (kg) = 20.41 (Length, meters)^2.728

Figure 5: Comparison between mass data for M. monoceros and D. leucas.

Maximum possible weight

Despite having covered a lot, there’s still one big dataset I have left. Using the weight model I developed earlier, I estimated the weight for 154 (excluding 3 emaciated outliers) St. Lawrence belugas captured during 1938-1939 (Vladykov, 1944). When compared to data collected from 1983-2012 (Lair et al., 2015), there seems to be less spread in the data for the estimated weights. There’s also no detectable discontinuity between juveniles and adults as found in the modern sample. These differences could be due to difference in sampling (commercial catch vs strandings), temporal differences in the condition of the stock, or due to the model not being sufficiently sensitive to variation in girth. The power function for the estimated masses of the 1938-1939 catch is as follows.

Mass (kg) = 19.40 (Length, meters)^2.820

Figure 6: Comparison of weight data for St. Lawrence belugas

Girth in the heaviest males typically exceeds slightly over 70% of the body length. Using this against the maximum confirmed length of about 590 cm for male belugas from the Okhotsk Sea suggest that they could theoretically achieve a maximum weight of 3,300 kg. However, Govorkov’s data implies such a mass is never achieved, and the maximum mass may be closer to 2000-2500 kg.

What’s next?

After finishing off with my work with monodontids, I will likely be moving on to the blackfish species. That will likely take only another few weeks as I’m already certain I’ve cleared most of the data available within the literature. The current tally for the entire database is 3,208 from literature and 3,850 from other databases. Let’s see what the total looks like by the time the next post is up.

I continue to invite anyone to who would like to share any information they feel could be relevant to the email below

cetologyh@gmail.com

References

Arsenʹev, V. A. (1935). Some data on the Beluga (Delphinapterus leucas Pall.) and its Catch in Sakhalin. Far Eastern Fisheries, 13.

Arsenʹev, V. A. (1936). Морфологическая характеристика дальневосточной белухи [Morphological characteristics of the Far East Beluga]. Bulletin of the Far Eastern Branch of the Academy of Sciences of the USSR, 19, 131–144.

Arsenʹev, V. A. (1939). Distribution and Migration of the Far Eastern Beluga. Izvestiya TNIRO, 15.

Barnes, L. G. (1984). Fossil odontocetes (Mammalia: Cetacea) from the Almejas Formation, Isla Cedros, Mexico. PaleoBios, 42, 1–46.

Bartholin, T. (1678). Thomae Bartholini De unicornu observationes novae: Secunda editione auctiores & emendatiores editae a filio Casparo Bartholino. Apud H. Wetstenium.

Beasley, W. L. (1904). The Largest Narwhal Tusk. Scientific American, 91(15), 251–251. https://doi.org/10.1038/scientificamerican10081904-251a

Bianucci, G., Pesci, F., Collareta, A., & Tinelli, C. (2019). A new Monodontidae (Cetacea, Delphinoidea) from the lower Pliocene of Italy supports a warm-water origin for narwhals and white whales. Journal of Vertebrate Paleontology, 39(3), e1645148. https://doi.org/10.1080/02724634.2019.1645148

Brodie, P. F. (1971). A Reconsideration of Aspects of Growth, Reproduction, and Behavior of the White Whale (Delphinapterus leucas), with Reference to the Cumberland Sound, Baffin Island, Population. Journal of the Fisheries Research Board of Canada, 28(9), 1309–1318. https://doi.org/10.1139/f71-198

Brodie, P. F., & Haulena, M. (2018). Dentinal growth layer counts of captive, known-age, mother and daughter belugas (Delphinapterus leucas): Confirming two growth layer groups (GLG/2) per year; consequences for recovery and management. Journal of Cetacean Research and Management, 18, 23–31. https://doi.org/10.47536/jcrm.v18i1.420

Brodie, P. F., Ramirez, K., & Haulena, M. (2013). Growth and maturity of belugas (Delphinapterus leucas) in Cumberland Sound, Canada, and in captivity: Evidence for two growth layer groups (GLGs) per year in teeth. J. Cetacean Res. Manage., 13(1), Article 1. https://doi.org/10.47536/jcrm.v13i1.550

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Progress on the small cetacean body mass database, with special reference to the genus, Kogia

Over the past month, I’ve been devoting more of my effort towards developing a database for the body masses of small toothed whales that I’ve began about 15 months ago. I’ve briefly mentioned this project in last month’s post dedicated to the body mass of river dolphins. I will now provide a broader overview of the database, along with some focus on the Kogiids. This can be considered a sequel to a twitter post I did about a year ago.

The diminutive sperm whales

Before getting into the dataset, I would like to provide a summary on the species of small sperm whales of the Kogia genus. These whales are recognized as the closest living relatives of the sperm whale (Physeter macrocephalus), though are currently assigned to a separate family, Kogiidae. They share some key similarities to Physeter, such as a singular blowhole, the spermaceti organ, and the reduction / lack of functional teeth in the upper jaw (Plön, 2004; Ross, 1979). Nonetheless, they aren’t close relatives, and the morphological differences suggest a divergence of over 20 millon years (Alfsen et al., 2021). The most obvious difference is that Kogiids are much smaller than Physeter, being only about the size of a typical dolphin at 2-4 m. The existence of two species, the pygmy sperm whale (K. breviceps) and the dwarf sperm whale (K. sima), was only officially recognized less than 60 years ago (Handley & Norris, 1966).

The two species are very similar, with the key differences being that K. sima is much smaller, possesses a larger dorsal fin, and appears to occasionally exhibit vestigial teeth in its upper jaw (Handley, 1966; Ross, 1979). The morphometry and growth for both species has only been extensively examined for the populations along Southern Africa (Plön, 2004; Ross, 1979, 1984). The only known set of growth parameters were yielded from the stranding records from this region coupled with a smaller sample from Australia (Table 1).

Table 1: Size parameters for Kogia species from South Africa and Australia (Plön, 2004)

Parameters	*K. breviceps* (M/F) (cm)	K. sima (M/F) (cm)
Size at birth	120	103
Size at Sexual maturity	242 / 262	215 / 197
Asymptotic size	286 / 306	263 / 249
Maximum size	327.6 / 330.5^a	260.4 / 274.3^b

a. Maximum length cited in text, though appendix records an individual of unknown sex measuring 339 cm (SAM 80/03).
b. Maximum length cited in text, but appendix records female measuring 286 cm (PEM N2773).

No precise length measurements exceeding 350 cm were recorded for K. breviceps within South African records (Plön, 2004). This species may grow larger in the Southeastern U.S. given records of females up to 427 cm (MME 8843) and males reaching 411 cm (Credle, 1988). The maximum length for K. sima in the USNM database (285 cm, MME 8069) more closely agrees with the South African data (Plön, 2004).

Building the database

In the current version of my compendium of body weights, I’ve divided my work into 14 somewhat arbitrary groups.

Kogia
River dolphins
Narwhals
Belugas
Pilot whales
False Killer whales
Other Blackfish
Risso’s
Bottlenose
Stenella
Delphinus
Porpoises
Current and Former members of Lagenorhynchus ‘’Lags and Ex-Lags’’.
Other dolphins (Cephalorhynchus, Steno, Lagenodelphis, Lissodephis, etc.)

Now you might notice two major groups not on here. I’m not going to name them, but many should who’s missing. Bear with me and trust me when I say I’ve excluded them for a good reason. It’ll make sense later.

Anyways, one of the major challenges in compiling body weight data for smaller cetaceans is that published data is far more abundant and widespread across sources. Because weighing larger species like humpback, blue and sperm whales is much more challenging, most of the existing data for a single species can be covered across several sources and nearly all the data was collected from whaling stations. Since weighing a dolphin is much easier, nearly every stranding record in the 20^th century becomes a potential source for weight data. I must therefore be more thorough than I am used to. Compilations of records provided by museum databases, like that of the Smithsonian, makes things easier. However, I wish to not solely rely on this as even these aren’t totally comprehensive.

Under the right circumstances, I will also digitize plots for weight data that that’s not directly provided in text (Figure 1). This was how I’ve obtained 118 of the 126 body weights analyzed in a review for Platanista (Braulik et al., 2021). My calibration and manual extraction appear to have been sufficiently precise, as my extracted data points perfectly matched the individuals that were listed in the review and other literature to the nearest cm and kg. I was able to identify about 13 of these replicates. I can only use this method for weight data plotted on the arithmetic scale below, as any imprecision for log-transformed values will introduce more error when back converting.

Figure 1: Data extraction for Platanista

My general process while collecting data is once I feel that I’ve comprehensively covered as much as I could from published literature for a certain group, I proceed to download the data from museum databases. For each group, I keep separate tallies for data I’ve compiled directly from literature versus data from databases. For Kogiids, I’ve compiled 127 records from literature and 118 records from the USNM database. I plot the data distinguishing both species in Figure 2. Some caution should be exercised when describing weight relationships primarily from stranding data, which is prone to emaciated outliers (Ross, 1984). My dataset of 245 kogiids excludes about 10 that I felt were obvious outliers.

Figure 2: Weight data for Kogia

The largest weights for K. sima were two males that were 260.4 cm / 272 kg and 256 cm / 303 kg. The largest female measured 264 cm and weighed 264 kg. Males were also the heaviest for K. breviceps (313 cm/ 700 kg, 315 cm / 680 kg, 351 cm / 680 kg) and the heaviest female was 285 cm / 540 kg. The heaviest females for both species were lactating.

Figure 3: Fields for data entries

Figure 3 shows the fields for each entry in the dataset. I record the species, sex, reproductive status for females (pregnant or lactating), measurements and their logarithmic transformations, sources, and lastly notes for specific details on each individual when warranted. The first few fields allow me to perform comparisons, such as the weight relationships between K. breviceps and K. sima. When comparing two models that did and did not include species ID as a variable, AIC model selection preferred the model that didn’t use species ID (delta for separate species model = 3.65, weight = 0.84).

As I’ve alluded to in my river dolphin post, AIC model criterion penalizes models that use too many variables. The difference (delta) in the AIC scores suggests that including species as a variable makes the model more complicated than it needs to be. This indicates that there’s not a significant difference in the inherent length-weight relationship between the two species. Pooling the data for both species yields the regression below in meters and kilograms. Figure 4 shows that the relationship for Kogiids is very similar for that of P. macrocephalus than it is for other groups (Brodie, 1971; Bryden, 1972; Cockcroft & Ross, 1989; Lockyer, 1976, 1993) .

Mass =18.1 (Length) ^2.777, R² = 0.918

Figure 4: Weight relationships for some odontocetes

Besides the data itself being abundant, the actual trickiest aspect of compiling this database is that a lot of data, especially museums specimens, are prone to being republished in reviews. Since the exact measurements for the same individual aren’t always consistent across sources, it’s very easy to have replicates of the same individuals if I’m not paying attention to dates, locations, and catalog IDs (Figure 5). This was especially the case for the South African samples of the Kogiid dataset (Plön, 2004; Ross, 1979, 1984).

Figure 5: Example of entries found in multiple sources.

I try to list all the notable references in the ‘’Source’’ field for each entry as it helps others using my dataset to be mindful of replicates. This also provides options for those who wish to check the literature directly, as some sources are less accessible than others. Since museum specimens are themselves often cited in literature, I primarily use the ‘’Notes’’ field for catalog IDs. This is especially important for filtering replicates when merging data from online museum records.

Current Progress

While I think my work is almost done for river dolphins and Kogiids, I still have some finalizing to do with some of the other groups I’ve mentioned earlier. I will say that in total, I have slightly over 2,600 individual records with extraction still underway for additional sources. Not sure what it would look like for the future, but I should be doing a new post each time I feel I’ve covered about 95% of what’s out there for a certain group. Once I’m done with every group, I’ll do a public release upon which I’ll continue to add incremental updates. Anyone with any questions, sources they wish to share with me, or requests for the database before it goes public can contact me at the email below.

cetologyH@gmail.com

References

Alfsen, A., Bosselaers, M., & Lambert, O. (2021). New sperm whale remains from the late Miocene of the North Sea and a revised family attribution for the small crown physeteroid Thalassocetus Abel, 1905. Comptes Rendus Palevol, 39. https://doi.org/10.5852/cr-palevol2021v20a39

Braulik, G. T., I. Archer, F., Khan, U., Imran, M., Sinha, R. K., Jefferson, T. A., Donovan, C., & Graves, J. A. (2021). Taxonomic revision of the South Asian River dolphins (Platanista): Indus and Ganges River dolphins are separate species. Marine Mammal Science, 37(3), 1022–1059. https://doi.org/10.1111/mms.12801

Bryden, M. M. (1972). Growth and development of marine mammals. In R. J. Harrison (Ed.), Functional anatomy of marine mammals (Vol. 1, pp. 1–80). Academic Press.

Cockcroft, V. G., & Ross, G. J. B. (1989). Age, Growth, and Reproduction of Bottlenose Dolphins Tursiops truncatus from the East Coast of Southern Africa. Fishery Bulletin, U.S., 289–302.

Credle, V. (1988). Magnetite and Magnetoreception in Stranded Dwarf and Pygmy Sperm Whales, Kogia simus and Kogia breviceps [MSc thesis]. University of Miami.

Handley, C. O., Jr. (1966). A synopsis of the genus Kogia (pygmy sperm whales). In K. S. Norris (Ed.), Whales, dolphins and porpoises (pp. 62–69). University of California Press.

Lockyer, C. (1976). Body weights of some species of large whales. ICES Journal of Marine Science, 36(3), Article 3. https://doi.org/10.1093/icesjms/36.3.259

Plön, S. (2004). The status and natural history of pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales off Southern Africa / [Thesis (Ph.D. (Zoology & Entomology))]. Rhodes University.

Ross, G. J. B. (1979). Records of pygmy and dwarf sperm whales, genus Kogia, from southern Africa, with biological notes and some comparisons. Annals of the Cape Provincial Museum (Natural History), 11, 259–327.

Ross, G. J. B. (1984). The smaller cetaceans of the south east coast of southern Africa. Annals of the Cape Provincial Museum (Natural History), 15, 173–410.

Brief note: On the mass of the large fossil river dolphin, Pebanista yacuruna.

One of my ongoing side projects is developing a comprehensive database of weight data for small odontocetes ranging from belugas, dolphins, pygmy & dwarf sperm whales, etc. It is naturally very challenging as such data is more widely collected as opposed to that of large species. Every now and again, I may be encouraged to dedicate a post to a certain portion of this dataset. Now appears to be a good time with the recent discovery and description of a prehistoric species of river dolphin (Benites-Palomino et al., 2024).

Introduction

‘River dolphin’ is a term used to describe several species of small odontocetes that have adapted to freshwater and estuarine environments, and are found in various parts of Asia and South America. Despite their name, most of these species exist outside of the families of oceanic dolphins and porpoises. Four these genera were once united under one family, Platanistidae, however they were eventually placed in their own families (Zhou, 1982).

Modern phylogenetic trees suggest that the La Plata dolphin (Pontoporia blainvillei), boto (Inia spp.), and the Chinese baiji (Lipotes vexifiller) form their own clade, while the South Asian species (Platanista spp.) evolved from a very basal lineage of toothed whales (McGowen et al., 2020). The Tucuxi (Sotalia spp.) actually are ‘’true dolphins’’ of the Delphinidae family.

Below I provide a summary of the average size of physical maturity (L_∞) and largest reliable sizes for some of the major species of each genus (L_max).

Table 1: Size parameters for different species of River dolphins

Species	L_∞ (cm) M/F	L_max (cm) M/F	Source
Inia geoffrensis^a	231.5 / 199.8	255 / 225	(Best & da Silva, 1984; Martin & Da Silva, 2006)
Platanista gangetica	205^b / 250^b	212 / 267	(Anderson, 1878; Braulik et al., 2021)
Pontoporia blainvillei^c	130 / 155	152 / 177	(Barreto & Rosas, 2006; Beneditto & Ramos, 2001; Botta et al., 2010; Kasuya & Brownell, 1979)
Sotalia guianensis	185^d	222 / 208	(De O. Santos et al., 2003; Meirelles et al., 2010; Ramos et al., 2010; Ramos & Lima, 2000)
Sotalia fluviatilis	—^b/ —^b	149 / 152	(Silva, 1994)
Lipotes vexiffiler	—^b/ —^b	229 / 253	(Brownell & Herald, 1972; Chen & Chen, 1975)

a. Corresponds specifically to those sampled from the Amazon River basin.
b. Data deficient.
c. Best reflects populations along coasts of southern Brazil, Uruguay, and Argentina. Populations from Rio de Janeiro, São Paulo, and Espírito Santo are quite smaller (Barreto & Rosas, 2006; Ramos et al., 2002)
d. There’s generally no consistent hints of sexual dimorphism as noted for other species (Lima et al., 2016; Rosas et al., 2003).

Caution should be placed in extending the values I report here to congeneric species or different morphs, as adult size and sexual dimorphism can vary considerably (Braulik et al., 2021; Silva, 1994; Silva et al., 2023). For Inia geoffrensis, older literature acknowledged a 274 cm male and 228 cm female respectively recorded in Peru (Layne, 1958) and the Orinoco river basin (Trebbau, 1975). However, it is suspected that these were not standardized measurements (Silva, 1994). So, for the time being, I will stick firmly with the largest individuals documented in more modern research.

Despite having been discovered in South America, the newly described fossil species Pebanista yacuruna is a close relative of the extant Ganges (P. gangetica) and Indus River (P. minor) dolphins (Benites-Palomino et al., 2024). On top of that very interesting detail, Pebanista is also quite large compared to any of the modern species, at an estimated range of 2.8-3.5 m based on the bizygomatic width (BZW) of these two specimens (Benites-Palomino et al., 2024). However, the authors consider these estimates to be conservative, as the BZW extrapolation is prone to underestimating the true size in similar taxa.

Mass data

I’ve currently assembled 414 individual weights for the above-mentioned genera that I’ve perused from existing literature and the USNM records. As can be seen in Figure 1, there’s a lot of variation at equal length. AIC model selection suggests that there’s a significant difference in the weight relationships between these species (ΔAICc= 72.09). This basically means that including the species as an additional variable justifies the cost of making the model more complicated, which is usually the case when the difference between two model’s AIC scores (ΔAICc) exceeds 2.

Figure 1: Mass data for River dolphin species.

As of now, I believe my dataset is comprehensive of the existing data for South Asian River dolphins, though it’s still a work in progress for other genera. I still lack a rather large sample (n=378) collected for the boto between 1994-2004 (Martin & Da Silva, 2006). I’m also aware of some larger datasets for Lipotes and Pontoporia, which I provide the existing regressions for in Table 2 (Brownell, 1984).

Update: 4:40 PM EST March 24th, 2024- I’ve since updated my dataset , which I can now proudly say is comprehensive for the existing weight data for the baiji (L. vexillifer) . I will leave Brownell’s regression, but will update the parameters for my baiji weight formula and the pooled sample. The corresponding mass estimates for Pebanista will also be updated.

Table 2: Mass-length formulae parameters for river dolphins

Genus	a^*	b	N	r²	Source
Pooled sample	13.30	2.672	430	0.90	Current post
Inia	15.37	2.553	129	0.84	Current post
Platanista	12.45	2.519	141	0.90	Current post
Pontoporia	14.16	2.231	89	0.88	Current post
Pontporia	15.43 (M) 13.42 (F)	1.518 (M) 2.512 (F)	75 (M) 56 (F)	0.78 (M) 0.95 (F)	(Brownell, 1984)
Sotalia	15.47	2.491	42	0.90	Current post
Lipotes	20.23	2.370	28	0.76	Current post
Lipotes	17.47 (M) 3.739 (F)	2.445 (M) 4.218 (F)	12 (M) 8 (F)	0.91 (M) 0.90 (F)	(Brownell, 1984)

*All constants of proportionality converted to units of meters and kilograms.

The maximum weight recorded from a non-pregnant river dolphin was 207 kg for a male boto from the Amazon (Martin & Da Silva, 2006). The corresponding length was not cited, so it was not included in the regression. Two baiji weighing 224 kg and 237 kg appear to be the heaviest pregnant individuals recorded (Chen & Chen, 1975).

Table 3: Mass estimates for Pebanista

Formula type	Holotype (280 cm) Mean mass (kg) (95% Prediction interval)	MUSM 3953 (347 cm) Mean mass (kg) (95% Prediction interval)
Pooled sample	208.9 (173.8-251.1)	371.2 (308.1-447.2)
Inia	212.9 (172.0-263.6)	368.2 (295.2-459.3)
Platanista	166.7 (132.5-209.6)	286.1 (226.0-362.2)
Pontoporia	140.9 (114.4-173.5)	227.4 (182.1-284.0)
Sotalia	201.1 (158.8-254.6)	343.1 (265.9-442.7)
Lipotes	202.7 (162.9-252.0)	337.0 (266.0-426.9)

Table 3 clearly shows that the expected mass for Pebanista varies greatly depending on the sample. In my opinion, the mass of Pebanista is probably best represented by either its closest relative, Platanista, or its modern ecogeographical counterpart, Inia. This would likely mean the typical adult of this species ranged from 150-300 kg.

Concluding thoughts

Aside from its large size and unusual geographic location, Pebanista is a very foundational discovery for our knowledge on the independent marine-freshwater transitions within Cetacea. This was an interesting departure from my typical focus on larger species. I got this post out late due to me trying to compare all the growth studies for the La Plata and Guiana dolphins. I’m looking forward to future opportunities to share progress on what will probably remain an ongoing effort until I’m dead.

References

Anderson, J. (1878). Anatomical and zoological researches: Comprising an account of the zoological results of the two expeditions to western Yunnan in 1868 and 1875; and a monograph of the two cetacean genera, Platanista and Orcella. B. Quaritch. https://doi.org/10.5962/bhl.title.50434

Barreto, A. S., & Rosas, F. C. W. (2006). Comparative Growth Analysis of Two Populations of Pontoporia blainvillei on the Brazilian Coast. Marine Mammal Science, 22(3), 644–653. https://doi.org/10.1111/j.1748-7692.2006.00040.x

Beneditto, A. P. M. di, & Ramos, R. M. A. (2001). Biology and conservation of the franciscana (Pontoporia blainvillei) in the north of Rio de Janeiro State, Brazil. J. Cetacean Res. Manage., 3(2), 185–192. https://doi.org/10.47536/jcrm.v3i2.889

Benites-Palomino, A., Aguirre-Fernández, G., Baby, P., Ochoa, D., Altamirano, A., Flynn, J. J., Sánchez-Villagra, M. R., Tejada, J. V., de Muizon, C., & Salas-Gismondi, R. (2024). The largest freshwater odontocete: A South Asian river dolphin relative from the proto-Amazonia. Science Advances, 10(12), eadk6320. https://doi.org/10.1126/sciadv.adk6320

Best, R. C., & da Silva, V. M. F. (1984). Preliminary Analysis of Reproductive Parameters of the Boutu, Inia geoffrensis, and the Tucuxi, Sotalia fluviatilis, in the Amazon River System. Report of the International Whaling Commission (Special Issue), 6, 361–369.

Botta, S., Secchi, E. R., Muelbert, M. M. C., Danilewicz, D., Negri, M. F., Cappozzo, H. L., & Hohn, A. A. (2010). Age and growth of franciscana dolphins, Pontoporia blainvillei (Cetacea: Pontoporiidae) incidentally caught off southern Brazil and northern Argentina. Journal of the Marine Biological Association of the United Kingdom, 90(8), 1493–1500. https://doi.org/10.1017/S0025315410001141

Braulik, G. T., I. Archer, F., Khan, U., Imran, M., Sinha, R. K., Jefferson, T. A., Donovan, C., & Graves, J. A. (2021). Taxonomic revision of the South Asian River dolphins (Platanista): Indus and Ganges River dolphins are separate species. Marine Mammal Science, 37(3), 1022–1059. https://doi.org/10.1111/mms.12801

Brownell, R., & Herald, E. (1972). Lipotes vexillifer. Mammalian Species, 44. https://doi.org/10.2307/3503836

Brownell, R. Jr. (1984). Review of reproduction in Platanistid dolphins. Report of the International Whaling Commission (Special Issue), 6, 149–158.

Chen, W., & Chen, Y.-Y. (1975). Notes on some morphological and anatomical features of the white-flag dolphin, Lipotes vexillifer, Miller. Acta Hydrobiologica Sinica, 5, 360–370.

De O. Santos, M. C., Rosso, S., & Ramos, R. M. A. (2003). Age estimation of marine tucuxi dolphins ( Sotalia fluviatilis ) in south-eastern Brazil. Journal of the Marine Biological Association of the United Kingdom, 83(1), 233–236. https://doi.org/10.1017/S0025315403007021h

Kasuya, T., & Brownell, R. Jr. (1979). Age determination, reproduction, and growth of the Franciscana Dolphin, Pontoporia Blainvillei. Scientific Reports of The Whales Research Institute Tokyo, Japan, 31, 45–67.

Layne, J. N. (1958). Observations on Freshwater Dolphins in the Upper Amazon. Journal of Mammalogy, 39(1), 1–22. https://doi.org/10.2307/1376605

Lima, J., Carvalho, A., Azevedo, C., Barbosa, L., & Serafim, L. (2016). Variation of age and total length in Sotalia guianensis (Van Bénéden, 1864) (Cetacea, Delphinidae), on the coast of Espírito Santo state, Brazil. Brazilian Journal of Biology, 77. https://doi.org/10.1590/1519-6984.13215

Martin, A. R., & Da Silva, V. M. F. (2006). Sexual dimorphism and body scarring in the Boto (Amazon river dolphin) Inia geoffrensis. Marine Mammal Science, 22(1), 25–33. https://doi.org/10.1111/j.1748-7692.2006.00003.x

McGowen, M. R., Tsagkogeorga, G., Álvarez-Carretero, S., dos Reis, M., Struebig, M., Deaville, R., Jepson, P. D., Jarman, S., Polanowski, A., Morin, P. A., & Rossiter, S. J. (2020). Phylogenomic Resolution of the Cetacean Tree of Life Using Target Sequence Capture. Systematic Biology, 69(3), 479–501. https://doi.org/10.1093/sysbio/syz068

Meirelles, A. C. O., Ribeiro, A. C., Silva, C. P. N., & Soares-Filho, A. A. (2010). Records of Guiana dolphin, Sotalia guianensis, in the State of Ceará, Northeastern Brazil. Latin American Journal of Aquatic Mammals, 97–102. https://doi.org/10.5597/lajam00157

Ramos, R. M. A., Beneditto, A. P. M. D., Siciliano, S., Santos, M. C. O., Zerbini, A. N., Bertozzi, C., Vicente, A. F. C., Zampirolli, E., Alvarenga, F. S., & Lima, N. R. W. (2002). Morphology of the franciscana (Pontoporia blainvillei) off southeastern Brazil: Sexual dimorphism, growth and geographic variation. Latin American Journal of Aquatic Mammals, 129–144. https://doi.org/10.5597/lajam00017

Ramos, R. M. A., Beneditto, A. P. M. D., Siciliano, S., Santos, M. C. O., Zerbini, A. N., Vicente, A. F. C., Zampirolli, E., Alvarenga, F. S., Fragoso, A. B., J. Lailson-Brito, J., Azevedo, A. F., Barbosa, L., & Lima, N. R. W. (2010). Morphology of the Guiana dolphin (Sotalia guianensis) off southeastern Brazil: Growth and geographic variation. Latin American Journal of Aquatic Mammals, 137–149. https://doi.org/10.5597/lajam00163

Ramos, R. M. A., & Lima, N. R. W. (2000). Growth parameters of Pontoporia blainvillei and Sotalia ﬂuviatilis (Cetacea) in northern Rio de Janeiro, Brazil. Aquatic Mammals, 26(1), 65–75.

Rosas, F., Barreto, A., & Monteiro‐Filho, E. (2003). Age and growth of the estuarine dolphin (Sotalia guianensis) (Cetacea, Delphinidae) on the Paraná coast, southern Brazil. Fishery Bulletin 101 (2): 377-383. Fishery Bulletin- National Oceanic and Atmospheric Administration, 101, 377–383.

Silva, V. M. F. da. (1994). Aspects of the biology of the amazonian dolphin genus Inia and Sotalia fluviatilis [Ph.D dissertation, University of Cambridge]. https://repositorio.inpa.gov.br/handle/1/38235

Silva, V. M. F. da, Brum, S. M., Mello, D. M. D. de, Amaral, R. de S., Gravena, W., Campbell, E., Gonçalves, R. da S., & Mintzer, V. (2023). The Amazon River dolphin, Inia geoffrensis: What have we learned in the last two decades of research? Latin American Journal of Aquatic Mammals, 18(1), Article 1. https://doi.org/10.5597/lajam00298

Trebbau, P. (1975). Measurements and some observations of the freshwater dolphin, Inia geoffrensis, in the Apure River, Venezuela. Zoologische Garten Jena, 45, 153–167.

Zhou, K. (1982). Classification and phylogeny of the superfamily Plantanistoidea, with notes on evidence of the monophyly of the cetacea. Scientific Reports of The Whales Research Institute Tokyo, Japan, 34, 93–108.

Comparing methods for fitting the allometric formula, with special reference to the weight relationship of the sperm whale

Biological allometry is the study of the different growth rates of body parts, or in other words, the change in anatomical proportions as body size increases. Allometry contrasts with isometry, where an organism’s proportions remain the same with increasing size. This concept was largely popularized by the early 20th century (Huxley, 1932), and the following power function is used to describe most allometric relationships.

y= ax^b

The conventional means of obtaining the “a” and “b” parameters is by transforming the data to their logarithmic values and fitting them to the linear model below. The log-linear model is then back-transformed to the above power function.

log ⁡(y) = b ∙ log⁡(x) + log⁡(a)

This formula is often attributed to Huxley himself, however, it was actually discovered earlier by a few other authors (Froese, 2006; Gayon, 2000). To predict the weight of fish, researchers developed the allometric power function as a modification of another formula (Thompson, 1917), which adhered to Galileo’s description of volume/mass varying with the cube of a body’s linear dimensions.

W= k ∙ L³

The simple cube law was insufficient as most fish species slightly deviate from a strictly cubic relationship due to changes in external proportions and body condition as they grow (Froese, 2006). Given that an exponent of 3 describes an isometric change in mass, the exponent ‘’b’’ is interpreted to indicate whether an animal’s body became relatively leaner ( < 3, negative allometry) or stockier (> 3, positive allometry) with increasing length (Froese, 2006). This method was then eventually applied to cetaceans (Schultz, 1938), and became the canonical means for cetologists to describe weight-length relationships. The linear model enabled ease of use for fitting and analyzing parameters.

Flaws in the traditional approach?

Despite being a deeply entrenched practice in many biological fields, the method of back-transforming the log-linear parameters has been the center of some criticism and controversy (Cawley & Janacek, 2010; Packard, 2012, 2023; Xiao et al., 2011). The log-transformation method inherently introduces bias in two manners: the linear regression is made to fit the geometric mean of the data, rather than the arithmetic mean (J. P. Hayes & Scott Shonkwiler, 2006; Smith, 1993) and smaller values are emphasized in the regression (Jansson, 1985; Packard et al., 2009; Packard & Birchard, 2008, 2008; Packard & Boardman, 2009).

Table 1

	Arithmetic values	Logarithmic values
	10	1
	100	2
	1,000	3
	10,000	4
Mean	11,110/4= 2,777.5	10^10/4= 10^2.5 = 316.23

Comparisons of arithmetic (left) and geometric (right) means of the same data

Table 1 illustrates the principle of the downward bias of geometric means and Figure 1 illustrates how the equal spacing of residuals (difference between observations and the predicted values) on the logarithmic scale is not maintained in the back transformation. In a regression, the general goal is to minimize the total sum of residuals between the fitted formula and the data. On the log scale (Figure 1A), fitting to the midpoint of the smaller values has the same impact as large values. On the arithmetic scale (Figure 1B), variance for the residuals increases greatly along the x-axis (known as heteroscedasticity). This means that directly fitting a nonlinear model on the arithmetic scale would place more emphasis on the larger values. By instead placing more weight on smaller values, the log-transformation method has been criticized for ‘’rotating’’ the model parameters from values that would provide a better fit on the arithmetic scale (Packard et al., 2009) .

Figure 1

Remedies for these problems are mainly split between the inclusion of correction factors (Beauchamp & Olson, 1973; D. B. Hayes et al., 1995; J. P. Hayes & Scott Shonkwiler, 2006; Smith, 1993) or directly fitting the nonlinear model on the arithmetic scale without any data transformation (Packard, 2012, 2023; Packard et al., 2009). Both approaches are largely ignored in recently published allometric formulae for whales (Agbayani et al., 2020; Christiansen et al., 2022; Fortune et al., 2021). Across nearly all the cetacean weight-length models in older literature, none of them were non-linear and only one used a correction factor (Odell et al., 1980).

Comparing fitting methods

To illustrate how the traditional log-linear fitting method compares to nonlinear regression, I’ve ran some analyses of all the piecemeal weight data for sperm whales that I’ve managed to compile from literature (n=58). All data were adjusted upwards by assuming 12% of the intact mass was lost to body fluids (Sleet et al., 1980). The traditional approach was performed by converting all the length and weight data to logarithmic values (base 10) and fitting the least-squares regression for the linear relationship. The linear model was then back transformed to the allometric power function. The nonlinear regression was performed by directly fitting the power function to the non-transformed data. The Levenberg–Marquardt algorithm through the glsnls function in R was used to find the least-squares solution for the nonlinear model. Table 2 provides a summary of the parameters.

Table 2

Type	a	b	units
Nonlinear model	0.0961	2.209	meters/ tonnes
Back-transformed linear model	0.0350	2.582	meters/ tonnes

The first thing that sticks out is how surprisingly low the ‘’b’’ parameter is in the nonlinear regression. Deviating this far from an approximately cubic relationship is conceptually unrealistic given the relatively subtle change in external proportions in sperm whales across postnatal growth (Nishiwaki et al., 1963). In Figure 2, it’s apparent that the nonlinear model’s shallow slope produces biased predictions for both the smallest and largest observations in the sample. Table 3 indicates that the downward bias in the linear regression is very minimal, predicting a mean weight that’s < 1% below the true value for the sample.

Figure 2

In short, it appears that giving larger values extra weight in the nonlinear regression undermines the underlying geometric relationship between linear dimensions and weight. While logarithmic transformation giving more weight to smaller values has been considered a disadvantageous ‘’distortion’’ (Packard et al., 2009), it appears to act more as a beneficial ‘’anchor’’ for estimating the true relationship of the allometric increase in body weight.

Table 3

Sample mean -Actual value (tonnes)	33.74
Sample mean -Nonlinear model estimate (tonnes)	33.83
Sample mean -Back-transformed linear model estimate (tonnes)	33.56

Connecting weight to growth

Figure 3

Tying this back to my last post, I’ve used the back transformed linear model to present growth curves for weight (Figure 3). This relationship can be calculated using a modified version of the von Bertalanffy formula, as used in previous works on whales (Lockyer, 1981), using the original parameters for total length that I calculated for males and those derived from stranding data for females (Evans & Hindell, 2004) . The 46% difference in asymptotic length between males in females results in a 166% difference in weight. As expected with negative allometry, this is below the expected 211% difference in weight of an isometric weight-length relationship.

Male Phase 1 (Ages 0-16): L(t)= 21.36 (1-e^{-13.85(t+3.25)})^2.582

Male Phase 2 (Ages 17 and older): L(t)= 43.62 (1-e^{-0.0741(t-0.0162)})^2.582

Female: L(t)= 16.38 (1-e^{-0.016(t-2.58)})^2.582

The linear model predicts that an exceptionally large female sperm whale measuring 12.5 m would weigh 23.8 tonnes (95% PI: 16.2-34.9) while an 18.3 m male would weight 63.6 tonnes (95% PI: 43.2-93.7). The record size of 20.7 m in modern literature corresponds to an estimated weight of 87.4 tonnes (95% PI: 59.0-129.4). That’s about twice the weight of the average male and over 3.5 times the weight of the largest female.

Parting news

As the current year ends, I wish to share some details regarding the weight analysis section of my upcoming manuscript. Despite presenting a large dataset of piecemeal weights in this post, absolutely none of it will be used for any new regressions in my review for the sperm whale. I will be using a different kind of data for that portion of my review. I truly am looking forward to sharing once the review process gets through as there is a lot that these past two posts don’t even scratch the surface of.

References

Agbayani, S., Fortune, S. M. E., & Trites, A. W. (2020). Growth and development of North Pacific gray whales (Eschrichtius robustus). Journal of Mammalogy, 101(3), 742–754. https://doi.org/10.1093/jmammal/gyaa028

Beauchamp, J. J., & Olson, J. S. (1973). Corrections for Bias in Regression Estimates After Logarithmic Transformation. Ecology, 54(6), 1403–1407. https://doi.org/10.2307/1934208

Cawley, G. C., & Janacek, G. J. (2010). On allometric equations for predicting body mass of dinosaurs. Journal of Zoology, 280(4), 355–361. https://doi.org/10.1111/j.1469-7998.2009.00665.x

Christiansen, F., Bejder, L., Burnell, S., Ward, R., & Charlton, C. (2022). Estimating the cost of growth in southern right whales from drone photogrammetry data and long-term sighting histories. Marine Ecology Progress Series, 687, 173–194. https://doi.org/10.3354/meps14009

Evans, K., & Hindell, M. A. (2004). The age structure and growth of female sperm whales (Physeter macrocephalus) in southern Australian waters. Journal of Zoology, 263(3), Article 3. https://doi.org/10.1017/S0952836904005096

Fortune, S. M. E., Moore, M. J., Perryman, W. L., & Trites, A. W. (2021). Body growth of North Atlantic right whales ( Eubalaena glacialis ) revisited. Marine Mammal Science, 37(2), Article 2. https://doi.org/10.1111/mms.12753

Froese, R. (2006). Cube law, condition factor and weight-length relationship: History, meta-analysis and recommendations. Journal of Applied Ichthyology, 22, 241–253. https://doi.org/10.1111/j.1439-0426.2006.00805.x

Gayon, J. (2000). History of the Concept of Allometry. American Zoologist, 40(5), 748–758. https://doi.org/10.1093/icb/40.5.748

Hayes, D. B., Brodziak, J. K. T., & O’Gorman, J. B. (1995). Efficiency and bias of estimators and sampling designs for determining length-weight relationships of fish. Canadian Journal of Fisheries and Aquatic Sciences, 52, 84–92. https://doi.org/10.1139/f95-008

Hayes, J. P., & Scott Shonkwiler, J. (2006). Allometry, Antilog Transformations, and the Perils of Prediction on the Original Scale. Physiological and Biochemical Zoology, 79(3), 665–674. https://doi.org/10.1086/502814

Huxley, J. S. (1932). Problems of relative growth. L. MacVeagh, The Dial Press. https://doi.org/10.5962/bhl.title.6427

Jansson, M. (1985). A Comparison of Detransformed Logarithmic Regressions and Power Function Regressions. Geografiska Annaler. Series A, Physical Geography, 67, 61. https://doi.org/10.2307/520466

Lockyer, C. (1981). Growth and energy budgets of large baleen whales from the southern hemisphere. Mammals in the Seas, 3(5), Article 5.

Nishiwaki, M., Ohsumi, S., & Maeda, Y. (1963). Change of form in the sperm whale accompanied with growth. Scientific Reports of The Whales Research Institute Tokyo, Japan, 17, 1–17.

Odell, D. K., Asper, E. D., Baucom, J., & Cornell, L. H. (1980). A recurrent mass stranding of the false killer whale, Pseudoorca crassidens, in Florida. Fishery Bulletin, United States. National Marine Fisheries Service, 78(1–2), Article 1–2.

Packard, G. C. (2012). Julian Huxley, Uca pugnax and the allometric method. Journal of Experimental Biology, 215(4), 569–573. https://doi.org/10.1242/jeb.061739

Packard, G. C. (2023). The logarithmic transformation in bivariate allometry. Biological Journal of the Linnean Society, 138. https://doi.org/10.1093/biolinnean/blad012

Packard, G. C., & Birchard, G. F. (2008). Traditional allometric analysis fails to provide a valid predictive model for mammalian metabolic rates. Journal of Experimental Biology, 211(22), 3581–3587. https://doi.org/10.1242/jeb.023317

Packard, G. C., & Boardman, T. J. (2009). A comparison of methods for fitting allometric equations to field metabolic rates of animals. Journal of Comparative Physiology B, 179(2), 175–182. https://doi.org/10.1007/s00360-008-0300-x

Packard, G. C., Boardman, T. J., & Birchard, G. F. (2009). Allometric equations for predicting body mass of dinosaurs. Journal of Zoology, 279(1), 102–110. https://doi.org/10.1111/j.1469-7998.2009.00594.x

Schultz, L. P. (1938). Can the Weight of Whales and Large Fish Be Calculated? Journal of Mammalogy, 19(4), Article 4. https://doi.org/10.2307/1374238

Sleet, R. B., Sumich, J. L., & Weber, L. J. (1980). Estimates of total blood volume and total body weight of a sperm whale (Physeter catodon). Canadian Journal of Zoology, 59(3), Article 3. https://doi.org/10.1139/z81-083

Smith, R. J. (1993). Logarithmic transformation bias in allometry. American Journal of Physical Anthropology, 90(2), 215–228. https://doi.org/10.1002/ajpa.1330900208

Thompson, D. W. (1917). On Growth and Form. Cambridge University Press.

Xiao, X., White, E. P., Hooten, M. B., & Durham, S. L. (2011). On the use of log-transformation vs. Nonlinear regression for analyzing biological power laws. Ecology, 92(10), 1887–1894. https://doi.org/10.1890/11-0538.1

A review of the growth and sexual dimorphism of the sperm whale (Physeter macrocephalus)

After summarizing the size for the largest baleen whales precisely one year ago, I return to provide an in-depth review for the sperm whale (Physeter macrocephalus). This will serve as a little teaser for the manuscript I’ve recently submitted, a literature review concerned with the maximum attainable size of the sperm whale.

The sperm whale is one of my favorite whale species alongside the bowhead (Balaena mysticetus) and the blue whale (Balaenoptera musculus). The high-quality oil within their spermaceti organ and the ambergris in their intestines made sperm whales a major target of every major nation in the commercial whaling industry. The two waves of commercial whaling in the 19^th and 20^th century are thought to have caused a 57% decline from a history population of nearly 2 million whales (Whitehead & Shin, 2022). The global population is now thought to be around 840,000. While abundant, this species may still face pressures from anthropogenic influences and are still feeling the effects of their populations having been disrupted.

P. macrocephalus is the only extant member of both the Physeter genus and Physeteridae family. Its closest extant relatives are the much smaller pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales within the Kogiidae family. Physeteroids were once a diverse clade, predominantly composed of macrophagous predators such as the Scaldicetus, Acrophyseter, Zygophyseter, Brgymophyseter, and the ever-popular Livyatan. However, even these fierce creatures are much smaller than the extant sperm whale, which remains the largest known species of odontocete to have ever lived.

Life History and Growth

The primary method of estimating age in tooth whales is counting the dentine layers in their teeth (Sergeant, 1962). These dentine layers were thought to form bi-annually (Berzin, 1964, 1972; Nishiwaki et al., 1958), however an annual formation rate akin to earplug laminae in baleen whales has been verified (Lockyer, 1981). Many growth curves have been published for sperm whales across the North Pacific (Berzin, 1972; Nishiwaki et al., 1958; Ohsumi, 1977), North Atlantic (Martin, 1980), and the Southern Hemisphere (Bannister, 1969; Best, 1970; Evans & Hindell, 2004; Gambell, 1972; Gaskin & Cawthorn, 1973). Growth curves are compared in Figure 1, showing relatively little regional difference in adult size.

Getting on to their size, sperm whales are typically born at about 4 m (Gambell, 1972; Matthews, 1938; Nishiwaki et al., 1958; Ohsumi, 1965). Weaning occurs by the second year at an average length of 6.7 m (Clarke, 1956). Female sperm whales sexually mature at 8-9 m in length after 7-10 years and physically mature at around 10.5-11 m after 20-30 years (Berzin, 1964; Best, 1970; Clarke et al., 2011; Evans & Hindell, 2004; Lockyer, 1981). Males continue to grow considerably larger. Sexual maturity in males has been interpreted to occur between 9-12.5 m after 9-20 years (Aguayo, 1963; Berzin, 1964; Clarke, 1956; Matthews, 1938; Nishiwaki, 1955; Nishiwaki et al., 1958). Further investigations revealed males reach full sexual maturity after 25 years and 13.7 m, with growth ceasing after 50 years at an average length of 15.2-16 m (Bannister, 1969; Berzin, 1964; Clarke et al., 1994; Gambell, 1972; Nishiwaki et al., 1958; Ohsumi, 1977). Sperm whales exhibit the most pronounced sexual dimorphism of any cetacean species.

Figure 1

Many of those familiar with fisheries studies and marine ecology are used to seeing growth curves fitted by logistic functions, such as the one shown below (von Bertalanffy, 1934, 1938).

L(t)=L_∞–(L_∞–l₀ ) e^-kt

The parameters included are age (t), the growth coefficient (k), length at birth (l₀), and the mean asymptotic length when a population is allowed to grow indefinitely (L_∞). The above form is how the von Bertalanffy growth model was originally presented, while the reparameterization below is the most widely-used version (Beverton, 1954) .

L(t)=L_∞(1-e^-k(t-t0))

Here, l₀ is replaced with t₀, which represents the age at which the length is zero. This constant is not an actual biological character, but an extrapolation of the post-natal growth trend. It should not be interpreted as the length of gestation.

There’s also another parameter, L_max, which is the maximum size observed within a population. Fish studies canonically interpreted that the L_max closely approaches L_∞ (Beverton, 1963; Parker & Stott, 1965; Pauly, 2002; Taylor, 1958). In reality, L_max may deviate significantly from L_∞, as mortality rates and the degree of individual variation can lead to L_max being much lower or higher than L_∞(Hordyk et al., 2015; Ricker, 1979; Schwamborn, 2018). Since the latter outcome universally applies to whales, I strictly distinguish these two parameters in contrast to some literature on cetacean growth that use the L_max notation as a synonym for L_∞(Garde et al., 2007, 2015; George et al., 1999; Lubetkin et al., 2012; Olsen & Sunde, 2002; Rosa et al., 2004).

Many of the earliest growth curves for sperm whales were fitted by hand (Berzin, 1964; Best, 1970; Gaskin & Cawthorn, 1973; Nishiwaki et al., 1958) as the non-uniform growth trends of large whales were poorly modeled by a single mathematical function (Chittlebrough, 1965). While the growth of females could be fitted by a single von Bertalanffy curve like smaller odontocetes (Bannister, 1969; Evans & Hindell, 2004), existing functions for males only provide good fits for post-pubertal growth (Bannister, 1969; Martin, 1980).

Recent studies for the growth of baleen whales obtained strong fits from two-phase models that transition at the age of weaning (Agbayani et al., 2020; Fortune et al., 2012, 2021; Lubetkin et al., 2012). I chose to apply a similar approach for male sperm whales using the raw data published for 3,045 individuals from the North Pacific (Kato, 1995; Ohsumi, 1977), 289 from the North Atlantic (Borrell et al., 2013; IJsseldijk et al., 2018; Martin, 1980; Mendes et al., 2007; Pagh et al., 2016), 240 from the Southeast Pacific (Clarke & Paliza, 1994)¹, and 8 from the South Atlantic (Degrati et al., 2011; Ramos et al., 2001).

¹(7/22/2023 Update: I’ve recently found that the raw age data that was analyzed in Clarke et al., 1994 was available in the appendix of the previous part of their studies of Southeast Pacific sperm whales. I have since updated figures 3&4 and the accompanying parameters to reflect this change)

Each observation was rounded to the nearest year and whole foot. Due to issues noted with sampling, labeling mistakes, and age estimation errors, I smoothed both the length and age distributions in accordance to a procedure outlined for a refined length key (Ohsumi, 1977). The length distributions obeyed a normal distribution while age distributions at a given length were notably right-skewed (Figure 2). Even after smoothing, the natural variation in size at a given age is very wide (Figure 3).

Figure 2

When fitted using the Solver add-in in Excel, a single von Bertalanffy function yielded the parameters below (r²= 0.720). The curve is plotted against the data in Figure 4. While the estimate for the L_∞is reasonable, t₀ is unrealistic. This echoes the aforementioned issues in modeling the growth of large whales.

L(t)=15.02 (1-e^-0.094(t-0))

Figure 3

Plotting the average length for each age (Figure 4) allows one to observe an inflection at around 16-17 years and 11.5 m in length. This represents the secondary growth spurt in male sperm whales (Best, 1970; Nishiwaki et al., 1963; Ohsumi, 1977). The same occurrence has been observed in the male growth curves of other polygynous odontocetes with pronounced sexual dimorphism such as pilot whales (Betty et al., 2022; Kasuya et al., 1988; Kasuya & Matsui, 1984; Sergeant, 1962), northern bottlenose whales (Benjaminsen & Christensen, 1979) and killer whales (Christensen, 1984). I used this point to mark the transition for a two-phase model listed below (r²=0.998). Phase 1 was fitted to the average size at birth (4.05 m) and weaning (6.7 m, age 2) reported in literature. The two-phase model was overall a considerably better fit over the single-phase model and provides a more reasonable estimate of 4.35 m for the size at birth.

Phase 1 (Ages 0-16): L(t)=11.99(1-e^{-0.1385(t+3.25)})

Phase 2 (Ages 17 and older): L(t)=15.81 (1-e^{-0.0741(t-0.0162)})

Figure 4

Figure 5 below shows the major growth stages for sperm whales outlined from using my two-phase model for males and an average curve for two von Bertalanffy functions for females (Bannister, 1969; Evans & Hindell, 2004). The stages of reproductive development in males adhere to the following definitions (Best, 1974).

Puberty-The stage at which 50% of whales are immature at the center of the testes, which corresponds to around 8.7-10.3 m at 9-10 years old (Bannister, 1969; Best, 1969; Clarke et al., 1994). Puberty appears to be what was referred to as sexual maturity by some early authors (Berzin, 1972; Clarke, 1956; Nishiwaki et al., 1958).
Sexual maturity– The stage at which 50% of whales are immature and 50% are maturing or mature at the periphery of the testes. This occurs at an average length of 11-12.9 m at 19 years old (Best, 1969, 1970; Clarke et al., 1994; Lockyer, 1981). This stage coincides with a growth spurt in the testes (Clarke et al., 1994; Gambell, 1972) and body size (Best, 1970, 1979; Best et al., 1984). By extension of the latter, this stage may occur at around 16 years for North Pacific males taken in the 1950-1970s (Ohsumi, 1977) .
Social maturity– The stage at which equal proportions of males are immature and mature at the periphery of the tests. Corresponds to a length of 13.7-14.4 m at 25 years old (Best, 1970; Clarke et al., 1994; Gambell, 1972). This parameter coincides with the deceleration of growth, sudden increase in testes size, full attainment of breeding status, and transition towards solitary living (Best, 1970, 1979; Clarke et al., 1994; Clarke & Paliza, 1988; Gambell, 1972; Gaskin, 1970; Kato, 1984).

Figure 5

Taxonomic history and anatomical differences between regions: multiple subspecies?

Linnaeus originally described 4 species of sperm whales : P. catadon, P. macrocephalus, P. microps, and P. tursio (Linneaus, 1758). As these names were synonymized, the latter two were phased out early and P. macrocpehalus ultimately won out over P. catadon due to first reviser priority (Husson & Holthuis, 1974). Apparent differences in size and external proportions have tempted Soviet authors to suggest that northern and southern sperm whales form distinct subspecies like in baleen whales (Berzin, 1972; Heptner et al., 1988; Tomilin, 1967). While analyses of external proportions show some clustering between individual regions (Machin, 1974), there was no clear division of northern and southern hemisphere whales. The growth curves (Figure 1) also suggest that apparent differences in average length of total catches are skewed by age segregation.

Genetic analyses have shown that there’s little genetic diversity across the global population of sperm whales (Lyrholm et al., 1999). While maternal genetic lineages within the mitochondria shows significant differentiation between populations, the biparentally-inherited nuclear DNA showed far less differentiation(Engelhaupt et al., 2009; Mesnick et al., 2011). This provides evidence for significant interoceanic male-mediated gene flow. The main exception to this trend is for Mediterranean sperm whales, appear to be very distinct from the Eastern North Atlantic population (Drouot, Berube, et al., 2004; Engelhaupt et al., 2009; Violi, 2020). IPI data revealed nearly no males exceeding 14 m (Caruso et al., 2015; Drouot, Gannier, et al., 2004; Pavan et al., 1997). In addition, two males measuring 12.2 and 12.8 m were found to be 40-44 years old (Frantzis et al., 2002; Maio et al., 2022). These whales would have likely physically matured around 12.5-13 m, approaching the minimum value of of 13.3 m reported in literature (Clarke et al., 1994). This evidence suggests that sperm whales from the Mediterranean are generally much smaller due to either genetics or possibly lower prey abundance in their low-latitude environment.

While there’s evidence suggesting that nutrition can lead to significant differences in growth between sperm whale populations (Best et al., 2016; Clarke et al., 1994; Kahn et al., 1993; Kasuya, 1991), the average difference in male growth is < 1 m. In Figure 6, I present the length frequencies of stranding records for male sperm whales from the Mediterranean (Cagnolaro et al., 1986; Centro Studi Cetacei, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994b, 1994a, 1995, 1996, 1998; Frantzis et al., 2002; Maio et al., 2022; Mazzariol et al., 2011). 35% of these males were reported reaching 15-19 m, which is congruent to the typical size range of mature bulls in other regions. All of these are from Italian strandings from between 1986-1995. While I am certainly convinced that sperm whales in the Mediterranean likely grow smaller on average, I doubt that slower growth is solely responsible for the apparent absence of males over 15 m in recent studies. I believe this discrepancy is a matter of some as-of-yet uncovered age segregation for Mediterranean males.

Figure 6

Maximum size

Like the blue whale, the precise maximum size (L_max) of the sperm whale has been a matter of contention. Historical records reported individuals measuring up to 23.1-27.4 m (Beale, 1839; Bennett, 1840; Starbuck, 1878). However these measurements were likely curvilinear lengths, leading experts to place the maximum length closer to around 18.3 m (Flower, 1868; Rice, 1989). It’s certainly correct that 18.3 m is exceptional for male sperm whales, although this may be a bit conservative for the precise maximum size. Interestingly, there are multiple records of bulls measuring between 18-18.6 m that were shown to be physically immature (Andrews, 1916; Boschma, 1938; Clarke, 1956; Kasuya, 1991), indicating they were still capable of further growth.

Reported measurements within the whaling data became more reliable after regulations and operational standards improved during the 1930s and 1940s (Branch et al., 2007; Donovan, 2000). Within this data, Guinness records recognizes a 20.7 m bull reported from the Kuril Island land stations in 1950 (Wood, 1972, 1976, 1982). While intentional data falsification plagued Soviet whaling data (Ivashchenko et al., 2011), this occurred more so during the 1960s. Data from the Kuril land stations from between 1948-1964 showed no signs of falsification (Ivashchenko et al., 2014). Prior to Guinness records, this whale was also cited as a record-holder by a very prominent Soviet cetologist (Zenkovich, 1954), who was unlikely to have been provided falsified data. Furthermore, the measurements within non-falsified Soviet data was among the most reliable of major whaling nations, as the Soviet industry was very keen on providing data to be utilized for biologists (Ivashchenko, personal comm., 2023). With all this in mind, the length of this individual was likely neither falsified nor an inaccurate measurement.

There are very few records of larger males that are considered reliable. A review of marine megafauna reports a bull captured in 1933 that measured 24 m (McClain et al., 2015). I will say that I have been recently analyzing the IWC catch data and saw that this whale was reported by Chilean fleets. As far as I’m aware, there were no regulations for Chilean whaling that would ensure accurate measurements prior to the formation of the Comisión Permanente del Pacífico Sur in 1952. In my upcoming article, I investigate whether such a size is even attainable.

The maximum size for females is a more complicated issue. Some literature have cited whaling records of females measuring of 15.9-17.4 m (Haldane, 1906; Nishiwaki, 1972; Tomilin, 1967) and a recent review has found that females reported from the Southern Ocean land stations had size-distributions that were nearly identical to males (McClain et al., 2015). However, records of such large females are often owed to typographic errors (Thompson, 1928) and whalers misidentifying the sex of males with retracted penises (Berzin, 1964; Matthews, 1938). The latter issue is prevalent even within modern whaling data, thus making it more difficult to precisely determine the limit in maximum size for female sperm whales.

The matter of sex misidentification becomes evident whenever comparisons are made to data collected by biologists. A 12.3 m female examined in the Azores was, at the time, the largest verified record known to most experts (Clarke, 1956). Since then, only a few other females measuring between 12.5-12.72 m have ever been reported (Andrews, n.d.; Guiler, 1978; Haase & Félix, 1994; Robson & Bree, 1970). I’ve performed some filtering within the IWC catch database that provided me a more reliable dataset of accurately identified females. This maximum I’ve arrived upon ended up being very interesting, which I will delve more into in my upcoming article.

Now in my previous posts, I tend to provide some emphasis on weight-length relationships, but that will also have to wait until my article is published. I worked very hard on it and had to delay it several times to follow up on some interesting leads, but I’m glad to say that it’s finally out of the way and I hope the peer-review process goes well.

For anyone interested in the dataset I’ve developed for my growth curve, contact me on cetologyh@gmail.com

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A world without the Blue whale: Battle for the throne of the largest animal in Earth’s history.

In one of last year’s articles, I was able to compile data to provide the size parameters for the largest animal in Earth’s history, the blue whale (Balaenoptera musculus). While the blue whale’s ranking amongst megafauna is well-recognized across the scientific community, there’s next to no definitive ranking for the second-largest, third, or even fourth largest. Well it may or may not come to surprise you that each of these are likely to be an extant whale species rather than a dinosaur!

The size-rivals

Outside of large whales, the other largest taxa of Earth’s history are the sauropods. For generations, these two groups have been interlocked in mortal combat in size comparison discussions, yet directly comparing their metrics can be problematic. The chief reason being the issues in precisely reconstructing taxa known only from fragmentary material. Mass estimates for sauropods are notably sensitive to differences in reference taxa, scaling formulas, measurement accuracy, etc. (1). As methodologies improved, sauropod mass estimates generally get downsized. One example is the dethroned Patagotitan, which was once estimated to weigh 70 tonnes, but current figures place it at 50-57 tonnes (1,2,3) Even relatively complete specimens aren’t immune, as the 26-meter subadult of Dreadnoughtus went down from its initial estimate of 59-tonnnes to 31-45 tonnes (2,3,4).

The existing figures for the masses of larger whales are also called estimates, but that can be misleading as 90-94% of a whale’s mass is directly measured in piecemeal weighings. The remaining portion is a conservative estimate of the body fluids lost the flensing process, which has been verified in experiments comparing whole weighing to piecemeal weighing (5). Unlike sauropod estimates, the calculated mass for whales leaves very little room for overestimation and are in fact more prone to the opposite as solid tissue, in addition to body fluids, can be lost in the flensing process.

Another problem is that sauropod mass estimates only provide a look at individuals. If my previous post on blue whales is anything to go by, size distributions across a population or species is a very important factor to account for. Unfortunately, that data isn’t available to us. We’re not entirely sure whether these mature individuals were small , average, or exceptional within their species. Since comparing sauropods to whale species isn’t exactly apples-to-apples, some allowance must be made.

When looking at the largest dinosaurs, Argentinosaurus huinculensis is considered the heaviest species by mass that’s known from decent material (3,6). The holotype is positioned to be around 70 tonnes while another specimen within its genus is calculated to have been slightly larger at 80 tonnes (7). Maraapunisaurus fragillimus may also be a good contender, but it’s known only from a giant vertebrae that is completely gone now. Like Argentinosaurus, M.fragillimus’ total length is estimated at around 35m, certainly surpassing even the largest blue whale in length. It’s thought to have weighed anywhere from 80-120 tonnes, though other recent estimates position it as low as 70 tonnes (3,7).

It seems that the most reliable mass estimates for sauropods top out at 80 tonnes, though if I stick too close to this, my article may become outdated by a new titanosaur, diplodocid, or mamenchisaurid that’s incrementally larger than Argentinosaurus. Due to the more restricted data present on sauropod masses, I will set the parameters for the ”largest sauropod” at 60-80 tonnes for the adult average with 100 tonnes as the maximum. I don’t want anyone saying I’m not giving them a fair shot.

Argentinosaurus (2)

Regardless of the leeway modern sauropod mass estimates are given, it remained scientific consensus that the blue whale outsizes these giants by a wide margin. Although several taxa are estimated to exceed the blue whale’s maximum length, many fall short in overall volume and mass. However, I rarely see discussions that settle on who has second place. Does that go to a sauropod, or another whale? I will present every species of whale that can be confidently estimated to outsize the largest sauropods.

The Overlooked Rorqual

Lets start off with the fin whale (Balaenoptera physalus). Fin whales are the type species for the genus Balaenoptera and are the second largest species of whale by length. Fin whales are very interesting creatures, but are often left ignored or overlooked due to being outsized by their more popular cousins. On a related note, I should warn those wishing to research this species to be careful. Older literature as recent as the early 20th century would often ignore Linneaus’ designations and assign fin whales to B.musculus while blue whales were referred to as ”B.sibbaldii” (8,9).

Like the blue whale, we have the 2 subspecies respective to the Northern Hemisphere (B.p.physalus) and the Southern Hemisphere (B.p.quoyi). Currently, there is debate on whether the North Pacific and North Atlantic populations should be elevated to separate subspecies (10,11). There is also a proposed pygmy subspecies that has yet to be rigorously validated; nonetheless, the designation is officially recognized (12). For this review, I will simply be focusing on the size parameters for the 2 major subspecies.

Like other rorquals, the southern subspecies is the largest of the fin whales. At birth, Antarctic fin whale calves are about 6-6.5 meters in length and grow to a length of 12 meters by 6 to 7 months of age (13). During the earlier years of commercial whaling, Antarctic fin whales were estimated to reach sexual maturity at 10-11 years of age, at lengths of 19.9 meters and 19.2 meters for females and males, respectively (14,15,16). As exploitation continued, fin whales began reaching maturity at younger ages of about 6-8 years old (16,17,18,19). It’s suspected this may be due to density-dependent changes in their environment. With depleted populations, individual fin whales have improved food availability, enabling them to grow at a faster rate. Fin whales physically mature at an age of 20-30 years (20,21). In the Antarctic, males cease growth at an average of 21 meters and females cease at an average of 22-22.9 meters (13,14,20,22).

As for the northern subspecies, very similar figures exist for the size at birth. Across the North Pacific and North Atlantic, the estimated length of sexual maturity ranges from around 17-18 meters for males and 18-19 meters for females (20,23,24,25). Research has shown a similar decline in age at sexual maturity as observed in the southern subspecies. However, no change in length was observed (25,26). On average, male northern fin whales enter physical maturity at 18.9 meters and females at 20.1 meters (24).

Fin whale life history

In the Northern Hemisphere, most individuals don’t grow much longer than 22-23 meters. The longest reports in the whaling record I could find was a 24.4-meter male taken in the North Atlantic in 1905 and a 24.7-meter female taken off the Pacific between 1919-1926 (8,27). However, due to issues with unstandardized measuring methods, rounding, or deliberate exaggeration, these records may potentially be inaccurate. However, Clapham makes the note that the fin whale catch records containing the 24.7-meter fin whale show signs of accurate measuring. Furthermore, there’s a mounted skeleton of a 24-meter male fin whale skeleton in Shanghai (28). When taking into consideration the sexual dimorphism of baleen whales, we can confidently claim a max length of >24 meters. Therefore, I consider 24.7 meters as the maximum length for females to be a reliable figure.

In the Antarctic, fin whales typically don’t exceed 24 meters. The largest female recorded by Mackintosh and Wheeler was 24.53 meters; while their text states that their largest male was 22.40 meters, both their tables and their appendix presents one male that was 23.60 meters (13). It was the only male to surpass 23 meters. The largest fin whale ever directly measured by a scientist was a 25.9-meter female (29) The largest I could find from whaling reports in the Southern Hemisphere was 27.3 meters for females and about 26.8 meters for males (30,31). Given that the average mature lengths for male fin whales is 2 meters greater in the Antarctic than in the north, the maximum length for male Antarctic fin whales shouldn’t be any less than 24 meters.

As for the whaling data, the 26.8m male was caught during the 1931/1932 whaling season. Aside from issues stemming from minimum-size restrictions enforced in later years, most of the unreliability for length statistics were less apparent by the 1930s. However, I am distracted by how in most years, the maximum lengths for males do not exceed 24-25 meters and most females very rarely exceed 26 meters. I am inclined to think this 26.8m male was either inaccurately measured or a female that was incorrectly identified.

Interestingly, the disparity between the whaling record and scientific record is about 1 meter for females. This can go either way as the difference can be owed to either sampling or measuring error. I think the 1934/35 whaling season provides a good idea of of the maximum lengths for both sexes: 25 meters for males and 26.8 meters for females (32). I think by this period, measurements for fin whales appeared more reliable as the largest reported individuals don’t often surpass 25.9-meters for females or 25-meters for males. This 25m/27m maximum for Antarctic fin whales conforms with general expert opinion (32).

Subspecies	Length at sexual maturity (meters)	Length at physical maturity (meters)	Maximum length (meters)
Northern	18.6 (females) 17.7 (males)	20.1 (females) 18.9 (males)	24.7 (females) 24 (males)
Antarctic	19.9 (females) 19.2 (males)	22.3 (females) 21 (males)	27 (females) 25 (males)

I will be approximating the masses by the same method outlined in my previous article on the blue whale but with some changes. Lockyer noted that her measuring of the seasonal fattening in the Antarctic was constrained by the lack of individuals present later in the feeding season (22). I’ve recently came across data acquired from the Japan’s scientific whaling expeditions in the Antarctic (18). In accordance with food availability enabling faster growth, whales were heavier at equal lengths than they were during the commercial whaling period. They also included specimens further into March, when whales are at their peak weight. The old data from commercial whaling estimates that fin whales can weigh up to 6.51 times their skeletal weight (22). Despite the JARPA weight data only presenting the length-wise averages for the individual components, I was able to reasonably approximate that by March, the body weight/bone weight ratio increases to around 8. The fattest individuals had a ratio of 8.8. With the new ratio of 5.65 for the lean weight, Antarctic fin whales appear to gain about 42% of their lean weight over the feeding period.

Along with these modifications for Antarctic fin whales, I will be using a different approach to the weight of northern fin whales. Studies have shown that they have unique tissue compositions and may not be directly comparable to their southern counterparts (34). The alternative regression I’m using is compiled from the weights of 40 northern fin whales cited in literature (5,34,35)

Subspecies	Mass at sexual maturity (metric tons)	Mass at physical maturity (metric tons)	Maximum Mass (metric tons)
Northern	41.7 (females) 36.3 (males)	51.8 (females) 43.6 (males)	92 (females) 85 (males)
Antarctic	46-65 (females) 42-60 (males)	59-83 (females) 52-73 (males)	85-120 (females) 74-105 (males)

It doesn’t seem that the northern fin whales will beat out the largest sauropod species except maybe with maximum mass. The Antarctic subspecies is much closer, and clearly has the edge in maximum mass. Historically, the lean nature of fin whales have been overstated, with older regressions suggesting that a 25-meter fin whale would weigh 70 tonnes (33). This is likely the consequence of having no data of either properly fattened or longer individuals for a long time. The data here clearly shows that a 25-meter fin whale’s mass would overlap with that of a blue whale’s at said length, which ranges from 86-128 tonnes.

Evidently, fattened fin whales will at least surpass the blue whale’s lean weight at an equivalent lengths. A maximum weight beyond 100 tonnes for a fin whale appears entirely feasible. However, the fin whale is not the 2nd heaviest extant whale after the blue whale, that title belongs to two other species.

The Corpulent Balaenids

If there are a group of extant animals that do not create as much noise as they should in discussion of megafauna, it’s the Balaenidae family. This group includes the three species of right whales (Eubalaena. spp) and the bowhead whale (Balaena mysticetus). These whales don’t grow as long as the fin whale, but their girths can approach or exceed 70% of their body lengths (37). At equal lengths, no whale can challenge their weight.

There are three species in the Eubalaena genus, but I personally think the standards for treating them as separate species rather than subspecies like in other baleen whales is mostly a convention. There were originally 2 species for the Northern (E.glacialis) and Southern Hemispheres (E.australis), but molecular studies revealed that the North Pacific population is closer related to the southern species than the North Atlantic population, warranting their own designation (E.japonica)(38). These whales were hunted for centuries and depleted by the 19th century. Of these three, only the southern species has made a significant recovery towards ‘Least Concern’ status.

The life history of North Atlantic right whales (NARW) has been the most rigorously examined. Newborns are estimated to be around 4-4.5 meters in length at the time of birth (39,40). Like rorquals, they rapidly grow within less than a year to 9.9 meters. NARWs are estimated to reach sexual maturity at around 8-9 years of age, corresponding to a length of 12 meters for males and 13 meters for females (40). When scaling these lengths at 90% of their physically-mature length, male NARWs cease growth at about 13.3 meters and females at 14.4 meters. This occurs as they approach 30 years of age. These parameters, however, may have changed for many individuals as a recent study found that entanglement has been stunting the sizes of NARW’s (41). The energetic costs incurred from dragging the nets impairs these whales’ growth, which in turn limits their calving rate. Nets pose a monumental threat towards their population recovery. Unlike other baleen whales, their southern counterparts (SRW) don’t seem to outsize them as the females appear to mature at the same size (42).

The one physical difference that truly distinguishes any of the right whales from each other is that the North Pacific right whale (NPRW) is much larger. Observations suggest newborns are larger in this species, but that’s difficult to discern as the rate of growth at this stage of life is rather rapid (37,43). Weaning is estimated to be at around 11 meters based on an 10.75-meter male that still had both milk and zooplankton in its stomach; individuals over 11 meters had no milk at all. Since no sexually mature individuals below 14 meters for either sex has been observed, males and females appear to enter sexual maturity at 14-15 meters (37,43,44). It’s estimated that both sexes physically mature at a range of 16-17 meters (37). This appears realistic given the frequency of adults of this length being caught or sighted.

Right whale life history

Maximum sizes are challenging to discern for the smaller two species. By the time scientists and whalers provided standard measurements, right whales were already seriously depleted and was lacking in older individuals. The largest NARW measured by a scientist was 16.5-meter female and the largest I could find in the 20th century whaling record was 18 meters. However, this could have been the length along the curve (45,46). Visual estimates from scientists in North Atlantic tagging expeditions indicate individuals possibly between 17-18 meters(47). When the Soviets illegally harvested SRWs, the largest measured 16.6 meters and 16.4 meters for females and males, respectively (48). The standard measuring technique was very common in the 1950s-1970s, so these are likely accurate figures. Given that males can exceed 16 meters, 17-18 meters for the maximum of female right whales in the North Atlantic and Southern Hemisphere appears likely. Since the size trends for SRW’s and NARW’s are so similar, they will be compiled together.

As for the North Pacific species, older whaling reports and visual sightings from Klumov suggest lengths exceeding 20 meters (43,46). Soviet catch records from their illegal harvests suggest a maximum of 18 meters and 19.8 meters for males and females, respectively (44). Given the inaccuracies from visual estimations and older whaling data, I think the more recent catch records are the best source.

Species	Length at Sexual Maturity (meters)	Length at Physical Maturity (meters)	Maximum Length (meters)
North Atlantic/ Southern Hemisphere	13 (females) 12 (males)	14.4 (females) 13.3 (males)	*17-18 (females) 16.4 (males)
North Pacific	15 (females) 14.5 (males)	17 (females) 16 (males)	19.8 (females) 18 (males)

*Approximate length based on maximum for males in Southern Hemisphere **Estimated range by Klumov (1962) and Omura (1969) with accounting for sexual dimorphism

Approximating weight is pretty straightforward as the three right whale species are nearly identical in morphology. A 2019 study by Fortune et. al combines North Pacific and North Atlantic weight data to improve on existing weight regressions, however there’s one minor issue (40). Some of the weight data provided was originally published in Klumov’s 1962 report and cited again by Omura in 1969 (37,43). Since only Omura’s report was available in English for decades, few in the anglosphere directly cite Klumov. I consulted the currently-available English translation for Klumov’s report and I learned that major components were unmeasured for 3 whales. While no adjustments were directly made to the figures, Klumov expressed in the text that 10-11 tonnes should be added to these whales (43). These adjustments were neither made nor acknowledged in Omura’s publishing of this data, and were thus not adjusted in Fortune’s 2019 study. Therefore, I’ve carefully measured what was missing from each whale and made conservative estimates for the missing parts based on weights from individuals of the same-length.

This regression is probably the best I have for a species. The data had a very tight correlation and it covered a wide portion of the adult length range, up to 17.4 meters. Some allowance should be made for each of the values in the chart as the data clearly shows major differences between individuals of similar length. I have not rigorously calculated it, but to give an idea, I generally see a gap as large as 10-20 tonnes between individuals in the 16-17 meter range.

Species	Mass at sexual maturity (metric tons)	Mass at physical maturity (metric tons)	Maximum Mass (metric tons)
North Atlantic/Southern Hemisphere	34 (females) 27 (males)	47 (females) 37 (males)	87(females) 71 (males)
North Pacific	54 (females) 48 (males)	79 (female) 66 (males)	127 (females) 95 (males)

The heaviest flensed weight measured for NPRWs was 106.5 tonnes from a 17.4-meter female; the intact weight would have been 114 tonnes (43). Unlike the rest of Klumov’s sample, this individual was carefully weighed by scientific personnel and every piece of it was accounted for. It’s the only direct weighing of any animal other than a blue whale that exceeds 100 tonnes. My regression predicts a mass of 85 tonnes for a whale of this length. It seems that weight can vary on the order of 20-30%, which agrees with weight range of 65-100 tonnes for 16-17m right whales that Klumov described (43). While accounting for this, it seems that a fattened right whale of over 19 meters could approach 150 tonnes. That’s about 3 times the weight of a blue whale at 20-meters! It’s clear from the weighings and this regression that we can confidently position NPRWs above any reliable sauropod estimate.

Now it’s time for the bowhead, a whale that will lead you down a few weird rabbit holes the more and more you learn about it. These whales are superlative by almost every convention: they have the largest skulls in the world that take up 1/3 of their body length, the thickest blubber, and the longest baleen that grows over 4 meters long in large individuals (49). They are also the only baleen whales that are residents of Arctic and subarctic waters. That’s just the tip of the iceberg!

The bowhead whale’s growth is quite unique from other baleen whales. Newborns are around 4 meters in length and rapidly grow after 12 months to 8-8.5 meters(49,50). As yearlings, bowheads are known as ‘ingutuqs’ by the Inuit hunters. Their increased girth and tissue were so different from other bowhead classes, hunters were convinced they comprised their own species (49,51). Unlike their relatives, bowheads cease growth for roughly four years. All the growth during these years is dedicated towards increasing the size of the head and baleen towards their adult proportions, which likely improves feeding efficiency (51). These juveniles are a lot leaner and are dubbed the ‘‘qairilik’’. By age 5, bowheads resume growth, but don’t reach sexual maturity until their mid-twenties (49,50,52). Females sexually mature at about 13-13.5 meters and males at 12.5-13.0 meters (49,50,52,53). Physical maturity is estimated to set in between 40-50 years of age at averages of 16 meters for males and 17 meters for females (49,52). Bowheads have amazing longevity, with several confirmed individuals that lived over 100 years, and one estimated at potentially 211 (49).

Bowhead whale life history (1)

As for the maximum length, the largest length ever reported was 21.3-meters from Yankee whalers and claims from Inuit hunters reported specimens measuring 22-24 meters (54,55). This sounds very similar to the alleged maximums for NPRWs. It should be noted that within aerial surveys, less than ~1% of bowheads have been detected to exceed 17 meters amongst 1800 photographs (49). Therefore, bowhead whales rarely approach 18 meters. Within modern fisheries data, the largest was a 17.37-meter male along with three records of females ranging from 19-19.5 m (49). The largest length recorded by subsistence whaling data was a 19.8 m specimen taken in between 1988-1992 (56). The sex is not stated, but the lack of records for males over 18 meters strongly suggest that this was a female.

Sex	Length at Sexual Maturity (meters)	Length at Physical Maturity (meters)	Maximum Length (meters)
Females	13-13.5	17	19.8
Males	12.5-13	16	17.37

Weight estimations for bowhead whales are a bit of an issue as very little weight data exists. Some data was collected for regressions, but predictions from length alone aren’t that great due to the low sample size and small body sizes of the weighed individuals (49,55). A regression that incorporated both length and girth was far more reliable. Testing this formula against independently-acquired volume measurements validated that it can accurately predict weights of large bowheads (49). I can use this better mass regression if I combine it with another formula that predicts the girth of a bowhead from its body length. To provide an upper-bound value for each mass, I will also be using the max-girth mean of 68% of the body length (49).

Sex	Mass at sexual maturity (metric tons)	Mass at physical maturity (metric tons)	Maximum Mass (metric tons)
Females	31-42	70-90	120-142
Males	28-38	57-75	75-96

As you might have been able to assume, the length-weight correlation for bowheads is very similar to the values presented for right whales, which was acknowledged by the authors (49). Another way a bowhead’s weight can be approximated is through its oil yield, as oil tends to compose a consistent fraction of a bowhead’s total weight (55). An oil yield of at least 230 barrels would predict a total weight of 100 tonnes for a bowhead. Yields exceeding 275 barrels were well-recorded and would correspond to 120 tonnes. The largest yields ever recorded were of 327 and 375 barrels; as far as I have read, the latter is the largest oil yield ever reported for a single whale. The body masses calculated from these yields would be about 144 and 164 tonnes. These approximations bolster my earlier claim that the largest right whales could approach 150 metric tons.

Final Ranking?

So in the end, it looks like at least three extant species of whales outsizes the sauropods:

Antarctic fin whales with average adult weights of 50-80 tonnes and a max weight of 120 tonnes
North Pacific right whales and bowhead whales, with adult masses ranging from 60-90 tonnes and maximum weights potentially approaching or exceeding 150 tonnes.

Argentinosaurus (3)

Is that all? Well yes. The next largest whale is the sperm whale, where females only range from 10-20 tonnes, but males average 35-55 tonnes and max out at 80. A bull sperm whale would certainly be comparable to some of the larger sauropods. However, when taking into account its own average weight and the species-average being brought down by the females, I can’t reasonably rank it above the Argentinosaurus. So I guess that’s all we’re done now… NOPE!

Triassic Giants!

Whales and sauropods have been recognized as the largest creatures in Earth’s history for generations, however ichthyosaurs have recently been making the scene over the past 2 decades. The fact they were the last group to be recognized for their size is ironic as the large Triassic ichthyosaurs were the first creatures of such size to exist on earth. Among these was a deep-bodied ichthyosaur that was estimated to reach up to 15 meters in length, Shonisaurus popularis of the Shastasaurid family (58). It was kind of the Brachiosaurus of its day, long touted a the largest, but has been dethroned by at least 2-3 other ichthyosaurs that were larger.

In 2004, a 21-meter ichthyosaur known as Shonisaurus sikanniensis was discovered (58). Even larger specimens were observed in the area, but no size estimates have been provided, even 18 years later (58). It is still the largest ichthyosaur that we know from good material. For some years, it was reassigned to the Shastasaurus genus, but has since switched back to Shonisaurus (59,60). Its designation under Shastasaurus created a lot of confusion for me in both conversation and research as this reassignment back to Shonisaurus wasn’t convincing t0 either the general audience or experts. Therefore, I will continue ro just refer to this species as just S.sikanniensis.

In addition to this, jaw fragments recovered from the United Kingdom revealed even larger individuals (61). The Lilstock specimen was estimated to be 25% larger than S.sikanniensis (26m) and the Aust Cliff ichthyosaur was estimated to be over 30% larger than the Lilstock specimen (>30m). However, due to their fragmentary nature, there are wide margins of error, as scaling from Besanosaurus resulted in a length of 22 meters for the Lilstock ichthyosaur. It’s even more shaky considering that the referenced total length for S.sikanniensis is an estimate itself. Still, regardless of the lack of precision, these animals were no doubt huge. They’re even suggested by many to be the most convincing contenders for dethroning the blue whale as the largest animal.

Now I bet those of you out of the loop are begging to see the mass estimates for these majesties. Unfortunately, that’s been a dry well for a very long time as only length estimates were focused on due to the trouble it takes to reconstruct ichthyosaurs. It was only recently that volumetric studies on recent reconstructions have allowed us to approximate S.sikanniensis’ and S.popularis’ weights at 80 tonnes and 20 tonnes at the lengths of 21 meters and 13.5 meters, respectively (62,63). However for S.sikanniensis, this mass is faulty. The volumetric model used to approximate this weight was constructed purely from S.popularis (63). In its description, the holotype of S.sikanniensis was described to have a slender body plan, and not deep-bodied like S.popularis. The max depth of its rib cage was only 1.90 meters. Therefore, this estimate is not reliable.

Despite many depictions portraying S.sikanniensis as a bulky animal, like a scaled-up S.popularis, it appears to have actually been leaner than a rorqual of equal length. I’m no expert myself on reconstructing extinct taxa, but I have seen paleoartists who claimed to have paid close attention to Nicholl’s and Manabe’s description give it a more slender body plan. When sticking to my strengths, I managed to comb through the literature on osteological studies on rorquals and have compiled about 12 specimens to get a rib length/total length regression.

Total length (meters)	Max rib length (centimeters)	Species
11.28	129.5	Sei (64)
12.30	141.0	Bryde’s (65)
13.70	157.3	Bryde’s (66)
14.70	177.2	Bryde’s (67)
15.30	209.0	Sei (68)
17.35*	210.0	Fin (69)
18.60	231.0	Pygmy Blue (70)
19.50	220.9	Fin (9)
20.50	255.5**	Pygmy Blue (71)
22.87	241.0	Blue (70)
25.00***	287.0****	Blue (72)
26.50	315.0	Blue (73)

*Length of reconstruction, without intervertebral tissue, the length was 14.6m

**Reported length for rib was ”10 feet”, I assumed to be the chord, not straight length. Used chord-straight length ratio from other studies on blue whales to arrive at this estimate, which
fitted the regression much better

***Estimated length for a fossil from a bizygomatic width regression for extant Balaenoptera. There were two other estimates of 22m and 23m from 2 other BZW-TL regressions, but the 25m estimate provided the closest expect rib length.

****Longest rib preserved. Used 60cm scale bar to approximate total length. Given its size, it was likely the 5-7th rib, which is sufficient enough for this regression.

Despite being a mixture of multiple species, the regression appears to have a tight, linear correlation of 11.162x + 12.011 ( R^2=0.9446). According to this formula, a rib-cage depth of 190cm is expected for a rorqual of 15.95 meters. Given that the figures in the 2004 paper shows that the ribs from S.sikanniensis aren’t any more widely arched than a rorqual’s, I figure their rib cages can be fairly compared. The JARPA II expedition collected the dorso-ventral heights from Antarctic fin whales, which had a ~250cm average for individuals 19 meters in total length (18). My regression approximates a rib cage depth of 220cm for a 19-meter fin whale, which means that dorso-ventral height appears to be 14% greater than the rib depth.

Given that most of these whales had a fattened body condition, I don’t think this type of ratio would risk shrink-wrapping S.sikanniensis. This is also falls in line with most skeletals I see for ichthyosaurs, which don’t extend soft-tissue outlines far beyond the silhouette of the skeleton. Assuming the flesh and blubber of S.sikanniensis covers the body as it does in a fat fin whale, 2.2-meters would be the estimated D-V height for S.sikanniensis. Going further, I can even use my ”whale-rib” regression to try estimating the weight for the S.sikanniensis holotype, Lilstock, and Aust Cliff specimens.

Shonisaurus sikkanniensis (1)

It’s reasonable, at this current time, to assume that these fragmentary specimens would have a similar body plan to S.sikanniensis as this species was the reference for approximating their lengths. Furthermore, the only other ichthyosaurs that are estimated to exceed 17m, like Cymbospondylus youngroum, are also quite slender (61). My process will be calculating the rib depth of the shastasaurid of a given length by scaling linearly from the shastasaurid holotype. This means that for a 22m shastasaurid, I will multiply 190cm by 22/21 for a rib depth of 199cm. I will then use my maximum rib-length regression to find the corresponding length of a rorqual, which is 16.75-meters. Afterwards, I will use Dr. Mikhalev’s weight regressions to find the weight of this rorqual and multiply it by the length difference (74). So this weight will be multiplied by 1.31 (22/16.75). I’m using Mikhalev’s regressions because they’re among the most optimized ones I could find for large rorqual species at a given length. They also can provide a decent prediction for seasonal fattening as the regression for Antarctic fin whales appears to correspond to my values for the fattened state.

To put things in simpler terms, I’m basically taking a whale, a creature we can reliably estimate the weight for, and manipulating its girth and length to match that of a shastasaurid. It’s not precise, but in lieu of a more rigorous method by experts or even knowledgeable amateurs, this is the best that I can do with the skill and knowledge at my disposal. Lengths of 22m and 26m will be tested for the Lilstock specimen and Aust Cliff specimens will be estimated at 30.8m and 36.4m. The latter two are based on a 40% scaling of the range for the Lilstock specimen.

Shastasaurid length (meters)	Mass-scaling from Sei whale (tonnes)	Mass- scaling from fin whale (tonnes)
21	26	34
22	31	39
26	49	64
30.8	78	105
36.4	126	170

These results are pretty much what I expected given S.sikanniensis’ dimensions. While no published source quoted masses for most of these sizes, I have read of others casually estimating a mass of around 30-tonnes for the holotype based on trying to scale up from smaller, more complete shasatsaurids like S.pacificus or Guanlingsaurus liangae.

More interestingly, Molina-Perez and Larramendi did publish a 60-tonne estimate for a 26-meter ”unnamed Shastasaurid”, which was likely the Lilstock specimen (7). Assuming they used a very valid method to approximate this mass, I feel feel pretty good about the range I’ve estimated. Besides that, it appears that the Lilstock specimen isn’t usurping any of the species I’ve covered, including Argentinosaurus. It would be, however, very comparable to the other larger sauropods or a bull sperm whale.

The Aust Cliffe specimen is interesting as at nearly 31-meters, its mass is only that of a 25-meter blue whale. Even at a length of a whopping 36.4 meters, it still doesn’t quite exceed the maximum mass for a blue whale, though it does get very close. Nonetheless, it firmly exceeds every other animal. And if it’s length is on the lower end, it might get overtaken by the balaenids and the largest fin whales in mass. Keep in mind, however, these estimates are actually stacking off of several layers of other estimates, even down to S.sikanniensis’ total length. If it turns that revisions to 17-19m for the total length of the holotype are correct, the downstream effect on these size estimates would be pretty amplified.

The Final Ranking

On one last note. I am revising my figure for the largest blue whale to be more conservative. Given the uncertainty of whaling records of blue whales exceeding the largest whale measured by a scientist (29.9m/ 98 feet), I consulted some extra resources to help me arrive to a reliable maximum length. I have come to the conclusion that a whale of 31.1-meters/102-feet can be considered a fair estimate for the maximum length. I came to this conclusion from three means.

If a recorded length 33-meters was actually taken along the whale’s curves, the true length would be approximately 31.3 meters as curve-lengths are about 6% greater than the standard measurement (75).
During the 1930s to 1940s, measuring issues like rounding did not disappear, but were still markedly less common than in earlier years(76). Accordingly, there was a notable change in the lengths of the largest blue whales. Between 1918-1930, blue whales up to 115 feet were recorded. Those exceeding 110-feet were most certainly inaccurate. From 1931-1949, the largest reported blue whales never exceeded 102 feet.
I was informed that a normal distribution for a large sample of carefully measured mature blue whale cows predicts a ~1/16,000 probability of one or more exceeding 100-feet. This left a 99.3% chance of 1 or more exceeding 100-ft amongst the >77,000 taken by whalers, but a 45% chance of any exceeding 102-ft. (T.Branch, personal communication, May 23rd,2022).

Together, the second and third points really make a strong case for my 31.1-meter figure. I still entertain a possible maximum around 32-33 meters, as normal distributions don’t always perfectly predict the behavior of real populations. For example, in a population of 7-billion humans, individuals the height of Yao Ming or greater shouldn’t exist within a normal distribution. At 7’6”, he’s 7.3 standard deviations away from the mean height of adult males. The equivalent distance for a female Antarctic blue whale would be 34.8m/114 ft (T.Branch, personal communication, May 23rd,2022) . Nonetheless, there’s currently not enough reliable data to conservatively support a maximum size greater than 31.1-meters.

How much would this whale weigh? Lockyer’s regression from 1981 predicts lean/fat weights of 144-215 tonnes (22). While no piecemeal weight was recorded for a whale of that length, I do have exciting information pertaining to what I covered in the bowhead section!

Apparently I was wrong in my previous article, 305 barrels is not the heaviest yield to come from a blue whale. In fact, a yield of 354 barrels was recorded for a 101-foot whale caught on March 21st, 1931 (77). According to the International Whaling Statistics, this whale was pregnant. When taking both this and the date of capture into consideration, this whale was most certainly in a fattened condition. Oil yield averages out to 24% of the flensed weight for a blue whale in the fattened condition according to Lockyer (22). The largest percentage in her dataset was ~28%, which was the case for a pregnant female. When dividing the reported weight of 56,640 tonnes of oil by these percentages, we get an intact mass range of 216-252 tonnes. If we assume oil yield can range up to 30%, then the lowest estimate would still be 202 tonnes! Given the pregnant status and length of the whale in mind, I think 200-216 tonnes is the most realistic range for this whale.

So at equal lengths of about 30.8 meters, a blue whale would weigh nearly twice as much a shastasaurid with S.sikanniensis‘ body plan. Even though my shastasaurid estimates are ballpark and using a not so perfect methodology, I still think they provide realistic weights for a marine tetrapod that has less girth than rorqual of equal length.

Argentinosaurus (7)

So here’s what the current ranking appears to be when ranking by mass

Antarctic blue whale
36.4-meter Shastasaurid
Tie between North Pacific right whale and bowhead whale
Antarctic fin whale
30.8m Shastasaurid
Argentinosaurus
& onward-Some of the other sauropods, Lilstock specimen, and bull sperm whale.

And now I’ve covered everything I wanted to get through. I hope you guys liked this. The writing and source gathering took a few months, but really, this article is a culmination of 2 years of work. Hopefully, any attention this article gets will influence a bigger push for more reliable mass estimates for Shastasaurids and maybe some photogrammetry data for blue whales in the Antarctic.

Acknowledgements

I would like to thank Dr. Trevor Branch for his contribution to this article. His expertise and shared interest in blue whales has been excellent resource for my own research.

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The Toughest in the Ocean: A review of killer whale predation of large whales.

Over millions of years, the ocean had been dominated by a select group of apex predators. After the rise and fall of Mesozoic marine reptiles, megatooth sharks, and macroraptorial sperm whales, the power vacuum is currently filled by one species, the killer whale (Orcinus orca). It truly is the apex predator of extant marine vertebrates, but the extent of their prowess is a matter of debate. This specifically concerns their predation on the largest extant animals, the great whales species. This controversy warrants a review of the documented records of killer whale’s hunting large whales, their behavior and techniques, and the assessed vulnerability of each species to killer whale predation.

Introducing the ”Whale Killer”

The killer whale’s reputation as a fierce animal is rooted in historical record across many cultures. Its genus name, ”Orcinus” pertains to a Roman god of the Underworld, Orcus. The English common name is likely derived from the name ”ballena asesina”, which meant ”whale killer” to Basque whalers. Across other European languages killer whales are called some variation of ”murder whale” or ”sword whale”. In Indigenous American populations like the Haida, ”Skana” means ”killer demon”. One of the words the Aleut have for this species, polossatik, means ”the feared one”. Clearly, the killer whale’s predatorial behavior has left an impact on everyone across the world. But is this reputation deserved?

It is true that the killer whale’s perception caused even experts to exaggerate their bloodthirsty nature. The most profound example was Dale Eschricht’s 1862 report on a killer whale, where he found pieces of 14 porpoises and 13 harbor seals (1). This report is often misquoted to suggest each specimen was present in its entirety! Nonetheless, the facts still speak for themselves, killer whales are the top predator with no equal in the ocean. In addition to fish, killer whales effectively predate on any pinniped or small cetacean species that overlaps with its distribution, even other dolphins as large as the false killer whale (Pseudorca crassidens) and beaked whales (2,3).

Sharks aren’t safe either. Killer whales have been documented directly attacking and killing great whites (Carcharodon carcharias). In fact, the threat of killer whales seems to be a selective pressure on the distribution of great white sharks (4). They also prey on even larger species like the basking shark (Cetorhinus maximus), attacking full-grown individuals exceeding 9.2 meters/30 feet in length (1,5).

Most impressively, killer whales are the sole predators for many calves and juveniles of large whale species (6). While rare instances have been also been observed with sharks, they often include entangled individuals who have already been brought to a debilitated state (7). On the contrary, killer whales themselves have no known predators. Not even a calf or juvenile has been known to fall victim to a large shark.

It should be noted that attacks of this scale are restricted to the mammal-specializing ecotypes such as the transients of the North Pacific, Type 2’s of the North Atlantic, and the Type A and B killer whales of the Southern Hemisphere. As a species, killer whales originally evolved from a piscivorous ancestor that was more like a conventional dolphin and evolved adaptations towards a macropredator niche (7). Over time, these ecotypes evolved into mammal-specialists independently.

While mammal-eating killer whales don’t form a clade of their own, they are very similar in their size parameters. The males in each of the ecotypes average 7.3-7.8 meters/ 24-26 feet in length at physical maturity while weighing 5.7-6.8 tonnes (9,10). The largest individuals from each ecotype have been confirmed to exceed 9 meters; a record-holding individual of 9.45-9.80 meters would weigh around 11 tonnes (11,12). By comparison, males of the fish-eating populations are comparatively smaller, with maximum lengths only slightly above 7 meters in length. They are even outclassed by the female mammal-eaters, who are similar in average length (6.4-6.9m) with a maximum length of 8.2 meters (10,11,12).

Killer whale size comparison — Size comparison between mammal eating and fish-eating killer whales.

Past this point is where this species’ abilities are called into question. While it was long accepted that killer whales are a danger to small cetacean species and young/compromised individuals of the larger species, experts disagreed on whether they consistently posed a threat to the healthy adults (6). Attacks have been witnessed over time for adults of all species, but successful kills aren’t always verified. Furthermore, beyond simply isolated events, there’s still the question of if these successful kills are frequent enough to have any major ecological impact.

Is anything safe from the orca? Time to find out.

To Kill a Leviathan

For a long time, it was assumed that adults of the great whale species were immune to predation from killer whales, but that’s being called into question. Interestingly, whales are categorized as either a ”fight” species or ”flight” species (13). It’s as simple as it sounds; fight species like sperm whales, balaenids, humpbacks, and gray whales are known to directly combat killer whales. Flight species , which encompasses each member of the Balaenoptera genus, avoid danger by running away with high bursts of speed. However, regardless of their size, they make no attempts to fight if the killer whales manage to slow them down. If they fail to outpace their pursuers, they’re done for.

To begin this review, I will start with the flight species. Specifically, the smaller rorquals such as the minke whale (Balaenoptera acutorostrata & B.bonariensis), bryde’s whale (B.edeni) and sei whale (B.borealis).

Adult minke whales are about 7-8m on average and reach maximum lengths of around 10-12m. Given their relatively small size, it should be no surprise that minkes are easily the most vulnerable amongst adult baleen whales. They are occasional prey to transients and Type B’s and are the primary prey item of Type A’s (14,15). However, even for this species, success can be hit or miss. While killer whales achieve higher top-speeds than minke whales, minke whales have better stamina, holding their speed over longer distances. For transient killer whales, successful hunts for minke whales is comparably far less frequent than for small toothed-whales and pinnipeds (14).

Successful attacks are rarer for the Bryde’s and sei whales than minkes, but have been verified. In 1988, a 12m Bryde’s whale was successfully hunted down by a group of killer whales in the Gulf of Mexico (16). Adult sei whales were killed after being chased into shallow waters near a salmon farm in Chile (17,18).

In all of these attacks, and in those to follow, killer whales display consistent strategies in taking on larger whales (6,13,14,16,17,18,19). They roughly follow this typical sequence:

Lowering vocalizations to avoid detection
Biting down on their flukes and pectoral fins to impede their movements
Leaping and slamming their bodies onto the whale to drown them
Ramming to inflict serious injury, often towards the jaw.
Will occasionally strip off and consume flesh off of whale while alive.

Now let’s cover some of the fight species: the Balaenids and the gray whale.

Killer whale in comparison to Bowhead whale, gray whale, and right whale.

The gray whale has a notable reputation for being a very violent and aggressive species when cornered, being dubbed the ”Devil Fish”. Before fighting, gray whales may try to utilized kelp beds to mask their presence from the orca’s echolocation (13). Despite these efforts , killer whales have been confirmed to kill adult gray whales as long as 12m. This suggests that calves aren’t the only vulnerable members of their species. However, most were juveniles less than 2 years old and 9 meters or less in length (20).

As for right whales, evidence is more scant when it comes to verified successful kills of large adults. Southern right whales (Eubalaena australis) with calves stick to shallow waters as the low depth limits the potential directions an orca can approach from to a 2D- plane. Futhermore, southern right whales were observed to form a ”rosette” formation in response to attacks . Here, the whales surround a calf or sick member with their heads facing inward and their tails out towards the killer whales. When not in a group, right whales will violently roll around and thrash their tails (13). In parts of the Southern Hemisphere, records of attacks on right whales shows no preference towards calves, with lone adults composing the majority of attempted attacks (21). This implies that adult right whales may be vulnerable to predation by killer whales. Nonetheless, adults have been seen to hold their own, as their tails manage to strike orcas clean out of the water.

Bowheads (Balaena mysticetus) often rely on retreating towards sea ice to protect themselves from killer whales (6,13). If caught, they violently thrash around in a similar manner to right whales. Eschricht once reported an instance where an orca was likely killed by the fluke of a panicked bowhead. According to Inuit hunters, adult bowheads were witnessed to be killed by larger groups of orcas (22). Among 18 bowheads described to have been killed by killer whales, only 8 were calf/yearling size (23). However, no precise size was described for the other 10. Since there is no report for a successful killing of adult bowheads outside of the accounts provided by the Inuit hunters, it’s likely these instances are rare. Studies of rake mark frequencies on bowheads in the Eastern Canada-West Greenland and the Bering-Chukchi-Beaufort Seas populations show higher rake mark percentages on larger individuals (24,25,26). Since these rake marks are being taken from whales that have survived, this means that hunting success is far lower when targeting older bowheads. Overall it seems that while bowheads are often targets, older ones are rarely taken.

Now we move on to the largest of the flight species: the fin and blue whales:

Comparison between blue whale, fin whale, and killer whale.

When it comes to fin whales, the only confirmed kill I could find was from a report with footage showing transient killer whales successfully hunting down a fin whale described to be ”at least 50 feet” (27). This would roughly correspond to a subadult if below 55 feet or maybe one just on the cusp of sexual maturity if closer to 60 feet. Another attack was reported for a group of 20 fin whales estimated to be 18-20 meters in length, but this was confirmed to be a failure (28).

As for blue whales, this hit the news pretty big this year. While there’s been a documented history of killer whales attacking blue whales, the outcomes were either failures or uncertain. Over the past few years, we’ve gained three confirmed accounts of killer whales successfully killing and eating blue whales (29). Two of these were calves ranging from 10-14 meters. The largest was estimated to be between 18-22 meters. For reference, a whale of this length would be roughly 40-60 tonnes. This is well within the adult range of the local pygmy blue whale population. From what the researchers could tell, this individual wasn’t emaciated either, it appeared to be healthy. Among the other reported attacks on blue whales, the largest ones were roughly 20m. This likely hints that larger blue whales may be more resistant to attacks, as a 23+ meter individual would be a lot harder to take down. Still, it appears that even the largest species on Earth isn’t immune to killer whale predation. However, there are still 2 more of the fight species to cover.

Killer whale, sperm whale, and humpback whale (1)

Sperm whales (Physeter macrocephalus) were long thought to be invincible to killer whale predation, however we now have many documented accounts showing that isn’t the case. Specifically, females and immature individuals have been killed many times by killer whales (6,30). Just like right whales, sperm whales deploy a rosette maneuver in combination with threat displays to defend against killer whales (19). While females and immature whales are known to be vulnerable, direct kills on bull sperm whales remains unconfirmed. In attacks where bull sperm whales were present, the killer whales were successfully driven off (31). Killer whales have only ever attacked large males who interfere in their pursuit of females or calves. In contrast to adult balaenids, bull sperm whales themselves are never the targets.

The sex-segregated distributions of sperm whales also hints that killer whales are significantly less of a threat to bulls. Upon reaching maturity, bulls move to live in high-latitude waters that are more densely-populated by killer whales. Females and juveniles stay in the lower latitudes where killer whales are less common. In consistency with the documented accounts, it appears that the mortality rate of bull sperm whales to killer whale attacks is exceptionally low compared to every other whale we’ve covered so far.

However, it still seems bulls are put off when they detect a killer whale’s presence. When exposed to killer whale sounds, male sperm whales immediately cease their solitary foraging and engage in social-antipredator defense (32). They oddly choose not to flee but prepare to stand their ground in response. This is likely the mechanism behind a group of males in Sri Lankan waters who broke off from their main pod to engage killer whales attacking a maternal group (31). So it seems we’ve covered our first creature that killer whales can’t seem to kill reliably, but they’re not the last.

While sperm whales are tough, humpbacks are the real mavericks! Not only has there never been a confirmed kill of an adult humpback by killer whales, but there are more documented instances of humpbacks attacking killer whales than the other way around (33). They remain the only species of large whales to actively mob killer whales and even go as far as to interfere when heterospecifics are targeted, like gray whales and seals. It’s speculated that this may be a form of animal altruism, though I wouldn’t entertain that. I think it’s more likely that the humpback interferes to the detriment of the killer whale rather than for the sake of the other species. If a humpback can help starve or injure a local group of orcas, that’s less to worry about during migration season. This behavior is consistent as humpbacks are very aggressive in general, where males are in heavy competition for mate access. It’s even speculated that their disproportionately large pectoral fins had evolved as weapons against killer whales (33).

So at the end of the day, it appears that amongst all the great whales: bull sperm whales and humpbacks are the best at holding their own. However, that’s just among the large whale species…

An unexpected challenger

Aside from an aggressive bull sperm whale or humpback, there’s another creature that seems to consistently intimidate killer whales, the long-finned pilot whale (Globicephala melas).

That’s right, long-finned pilot whales seem to have a rampant history of mobbing killer whales in the North Atlantic. Despite their smaller size, they seem to overwhelm killer whales with their raw numbers. Studies looking into this behavior have uncovered that the killer whales that are being chased off do not predate on pilot whales, nor do they compete for the same prey (34). This led to the hypothesis that pilot whales are confusing these harmless killer whales with a separate mammal-eating population that had gone extinct. Assuming this behavior is learned and is most likely passed down matrilineally, I amusingly refer to this explanation as the ”Racist Grandma” hypothesis.

Outside of the North Atlantic, this behavior is observed in other regions, as larger groups of pilot whales immediately rushed to the scene in 2 out of 3 recorded blue whale killings (29). There were no direct interactions, but it is likely that they were attracted to the vocalizations of killer whales.

So there you have it, whales that killer whales cannot confidently defeat: bull sperm whales, humpback whales, and long-finned pilot whales.

Remaining Mysteries

Now an interesting topic regarding killer whale hunting behavior is the role of adult males in attacks on large whales. It was once assumed males were necessary for successful kills (28), but that has been debunked many times (6,13,29). Very often males would remain in the periphery during hunts and may occasionally participate near the end (6,14,16,29). Meanwhile, females and subadults are performing most of work. It’s proposed that females are given priority in these hunts because they have more young to feed (29). Alternatively, it may be because mature males experience extra drag from their proportionately larger pectoral and dorsal fins. Couple this with being much larger than females, their stamina would deplete in chases against flight species and would lack the maneuverability for pursuits leading to shallow water (14). I think this hypothesis works out as males were far more common and active in attacks on the slower fight species and minke whales in offshore waters (6, 21,31,32,33).

Another big question is what influence mammal-eating killer whales have on the population dynamics of mature individuals. It has been long-believed that calf mortalities to killer whales was a huge selection pressure in driving the distributions and migration routes of large whale species (6,13). By contrast, I don’t think the direct hunting of mature baleen whales has a strong ecological impact. I believe that the killer whale’s effect on populations of large whales is primarily on the immature cohort as most sources show that juveniles and calves make up the majority of documented kills for species larger than minkes (6,13,23,24,25,26). These findings are also supported by studies where the vast majority of individuals within observed baleen whale species receive their rake marks as calves and only a minority receive new ones over time (35,36). Even the adults that are killed are smaller than average, like the 20-meter blue whale or the 15-16 meter fin whale. It is very likely that Antarctic blue whales, where the average adult is 25-meters long and twice as heavy as the recently-documented pygmy, is virtually immune to killer whales.

Nonetheless, the current research still shows we’ve been underestimating killer whales and the impact that they do have on immature baleen whales. Which may be a concern for bowhead whales, as loss of sea ice in the Arctic is increasing the frequency of attacks on calves and juveniles. Without the ice, killer whales are able to remain in Arctic waters for longer periods of time (23,24,25). It’s also not outside the realm of possibility that other baleen whales will become increasingly vulnerable from poor health conditions due to climate change or net entanglements, echoing this previously unseen great white shark attack on a juvenile humpback (7). Killer whale predation can be a potentially large threat to recovering whale populations when compounded with anthropogenic influences.

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Sironi, M., López, J., Bubas, R., Carribero, A., & García, C. (2008). Predation by killer whales (Orcinus orca) on southern right whales (Eubalaena australis) off Patagonia, Argentina: Effects on behavior and habitat choice.
Ferguson, S. H., Higdon, J. W., & Westdal, K. H. (2012). Prey items and predation behavior of killer whales (Orcinus orca) in Nunavut, Canada based on Inuit hunter interviews. Aquatic Biosystems, 8(1), 3. https://doi.org/10.1186/2046-9063-8-3
Willoughby, A. L., Ferguson, M. C., Stimmelmayr, R., Clarke, J. T., & Brower, A. A. (2020). Bowhead whale (Balaena mysticetus) and killer whale (Orcinus orca) co-occurrence in the U.S. Pacific Arctic, 2009–2018: Evidence from bowhead whale carcasses. Polar Biology, 43(11), 1669–1679. https://doi.org/10.1007/s00300-020-02734-y
Reinhart, N., Ferguson, S., Koski, W., Higdon, J., Leblanc, B., Tervo, O., & Jepson, P. (2013). Occurrence of killer whale Orcinus orca rake marks on Eastern Canada-West Greenland bowhead whales Balaena mysticetus. Polar Biology, 36, 1133–1148. https://doi.org/10.1007/s00300-013-1335-3
George, J., Sheffield, G., Reed, D., Tudor, B., Stimmelmayr, R., Person, B., Sformo, T., & Suydam, R. (2017). Frequency of Injuries from Line Entanglements, Killer Whales, and Ship Strikes on Bering-Chukchi-Beaufort Seas Bowhead Whales. ARCTIC, 70, 37. https://doi.org/10.14430/arctic4631
George, J. C., Philo, L. M., Hazard, K., Withrow, D., Carroll, G. M., & Suydam, R. (1994). Frequency of Killer Whale (Orcinus Orca) Attacks and Ship Collisions Based on Scarring on Bowhead Whales (Balaena Mysticetus) of the Bering-Chukchi-Beaufort Seas Stock. ARCTIC, 47(3), 247–255. https://doi.org/10.14430/arctic1295
Orcas attack, kill large fin whale off La Paz (rare footage)—Pete Thomas Outdoors. (n.d.). Retrieved May 8, 2022, from https://www.petethomasoutdoors.com/2013/07/orcas-attack-kill-large-fin-whale-off-la-paz-rare-footage.html
Behavioral observation on fin whale, Balaenoptera physalus, in the presence of killer whale, Orcinus orca. Fishery Bulletin 87:370-. 373.
Totterdell, J., Wellard, R., Reeves, I., Elsdon, B., Markovic, P., Yoshida, M., Fairchild, A., Sharp, G., & Pitman, R. (2022). The first three records of killer whales ( Orcinus orca ) killing and eating blue whales ( Balaenoptera musculus ). Marine Mammal Science. https://doi.org/10.1111/mms.12906
Pitman, R. L., Ballance, L. T., Mesnick, S. I., & Chivers, S. J. (2001). KILLER WHALE PREDATION ON SPERM WHALES: OBSERVATIONS AND IMPLICATIONS. Marine Mammal Science, 17(3), 494–507. https://doi.org/10.1111/j.1748-7692.2001.tb01000.x
Nanayakkara, R. P., Sutton, A., Hoare, P., & Jefferson, T. A. (2020). Killer Whale Orcinus orca (Linnaeus, 1758) (Mammalia: Cetartiodactyla: Delphinidae) predation on Sperm Whales Physeter macrocephalus Linnaeus, 1758 (Mammalia: Cetartiodactyla: Physeteridae) in the Gulf of Mannar, Sri Lanka. Journal of Threatened Taxa, 12(13), 16742–16751. https://doi.org/10.11609/jott.5006.12.13.16742-16751
Curé, C., Antunes, R., Alves, A. C., Visser, F., Kvadsheim, P. H., & Miller, P. J. O. (2013). Responses of male sperm whales (Physeter macrocephalus) to killer whale sounds: Implications for anti-predator strategies. Scientific Reports, 3(1), 1579. https://doi.org/10.1038/srep01579
Pitman, R. L., Deecke, V. B., Gabriele, C. M., Srinivasan, M., Black, N., Denkinger, J., Durban, J. W., Mathews, E. A., Matkin, D. R., Neilson, J. L., Schulman-Janiger, A., Shearwater, D., Stap, P., & Ternullo, R. (2017). Humpback whales interfering when mammal-eating killer whales attack other species: Mobbing behavior and interspecific altruism? Marine Mammal Science, 33(1), 7–58. https://doi.org/10.1111/mms.12343
Stephanis, R., Giménez, J., Esteban, R., Gauffier, P., García-Tiscar, S., Sinding, M.-H., & Verborgh, P. (2014). Mobbing-like behavior by pilot whales towards killer whales: A response to resource competition or perceived predation risk? Acta Ethologica. https://doi.org/10.1007/s10211-014-0189-1
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Killer whale predatory scarring on mysticetes: A comparison of rake marks among blue, humpback, and gray whales in the eastern North Pacific. (). https://doi.org/10.1111/mms.12863
Killer whale predatory scarring on mysticetes: A comparison of rake marks among blue, humpback, and gray whales in the eastern North Pacific. (n.d.). https://doi.org/10.1111/mms.12863

The Blue whale: Putting the largest animal under the microscope.

Okay, today’s article will be a return to a familiar topic. Before, I gave a broad look at the sizes of various species of whales and the methodology for how they were calculated. Today will be a more in-depth look at the blue whale’s size and growth. I personally believe it’s an interesting topic and many casual sources tend to oversimplify or misleadingly report specific statistics. I aim for this post to provide a robust breakdown about the size of the blue whale.

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Introduction: Nomenclature and taxonomy

The blue whale was first scientifically described by Scottish naturalist, Robert Sibbald in 1692, based on his discription of a 23.79 meter (78-foot) specimen stranded in Firth of Forth (1). Thus one of its common names was the Sibbald’s rorqual. In 1758, Carl Linnaeus gave the blue whale its current scientific name, Balaenoptera musculus. The species name forms an amusing pun as the ”musculus” is derived from that latin term for ‘little mouse’, referring to how muscle movements under the skin resemble mice scurrying beneath a cloth. The blue whale was also known as the ”sulphur-bottom” by American whalers as diatom growth beneath the whale left a yellowish pigment. The blue whale’s current name was coined by Sven Royn, who developed the harpoon gun that finally allowed the whaling industry to hunt blue whales in the late 19th century (2). Along with being recognized as the largest animal in Earth’s history, it’s also among the most mysterious as we still know very little about this whale.

The blue whale is currently divided into five subspecies throughout the world (3). Blue whales of the Northern hemisphere (B.m. musculus) and the Antarctic (B.m. intermedia) were the first two to be divided based on their offset breeding seasons. Eventually, the blue whales of the Southern hemisphere became further delineated as a pygmy subspecies (B.m. brevicauda) was recognized in the 1960s by Dr. Tadayoshi Ichihara . The blue whales in the North Indian Ocean and Arabian sea (B.m.indica) are physically similar to pygmy blue whales, however, they breed asynchronously from other Southern hemisphere blue whales and possess distinct call types. The latest subspecies to be classified is the Chilean blue whale, which still remains scientifically unnamed. The Antarctic subspecies will be the greater focus of this topic, but the other subspecies will also be discussed.

How blue whales were measured

In both whaling and scientific practices, the standard method for measuring a whale’s total length is from the tip of its rostrum to the notch between its flukes. This method was adopted as the flukes themselves were often cut off to prevent drift as the whale was towed by whaling ships. The rostrum acts as the anterior endpoint because the jaw was rarely in its natural position when the body was placed on the flensing platform (4,5). This ‘total’ length is notably shorter than a whale’s ‘overall’ length from the tip of the flukes to the tip of the jaw. One blue whale that had an overall length of 29.0 meters/95 feet had a total length of 27.4 meters/90 feet.

This blue whale model, from the rostrum to the notch of its flukes, measures about 37.3 centimeters.

When it comes to weight estimates, there exists no measuring of a blue whale in its entirety. Whales weighed in whole were smaller whales like beaked whales, minkes, and occasionally large sperm whales using either weighbridges or cranes (5,7,8). All data of blue whale weights were measured piecemeal using pressure cookers or dynamometers (9,10,11). The first piecemeal weighing was conducted in 1903 for a 23.7-meter blue whale that only weighed 63 metric tons (5,12). It was very laborious work and was done in very awful weather as many of them were specimens collected from the Antarctic. Furthermore, when the whales are flensed into pieces, most of their body fluids are lost, which may account for 5-8 percent of their total weight. When plotting these weights with the length of each whale, a whale’s weight can be predicted from its length by using a power function formula. However, for rorquals especially, the application of these formulae are limited, which will be discussed later.

How Big Is The Average Blue Whale?

The size of the typical blue whale varies greatly and depends on multiple factors. The most important of these is the subspecies. One of the key characters for separating the different subspecies of blue whales are differences in average length between the adult populations (4, 13,14). Along with measuring the whale’s length, scientific studies also measured the development of sexual organs and skeletons to determine the size at which blue whales attained sexual and physical maturity (15).

The most rigorously examined and well-established growth parameters are for the Antarctic blue whale. As newborns, Antarctic blue whales are about 7-8 meters long and weigh 2-3 metric tons (1,9,15). From the high-fat content of their mother’s milk, they grow at an astonishing rate to about 16 meters and gain about 17,000 kilograms (1,6,15). They achieve this size in only about 7 months from birth! At around 10 years old, Antarctic blue whales enter sexual maturity when females are about 23.4-23.7 meters long and males are 22.6 meters long (15,16). These values are known as the L50, the length where 50% of whales are sexually mature and 50% are immature. As they grow older, the vertebral column fuses, preventing further growth. On average, female Antarctic blue whales physically mature at over 26 meters and males at 25 meters (6,15). The average lengths of the overall adult population are 24.3 and 25.6 meters for males and females, respectively (14). These values are known as the Lmean. The maximum length for this subspecies is a matter of some controversy, but the more convincing whaling resources suggest 33.26 meters for females and 32.64 meters for males (1,5,16).

Blue whale life history graphic

Pygmy blue whales, by contrast, are notably smaller. Newborns are about 5.6-5.8 meters long on average (9). Pygmy blue whales have L50 values of 18.6 meters and 19.2 meters for males and females, respectively (13,17). Male pygmy blue whales physically mature at 21.1 meters and females at 21.6-21.9 meters. The Lmean for the pygmy blue whale population is around 21.0 meters for females and likely about 20.3 for males. The maximum length for a pygmy blue whale is 24.2 meters for females and 23.8 for males (14,34). The physical traits of the North Indian blue whale are currently poorly distinguished from the pygmy blue whale. One study found the L50 of B.m.inidica to only be 0.5-0.6 meters shorter than that of the pygmy blue whale (17).

The growth parameters for the Chilean blue whale are less defined as this subspecies’ identification is very recent. Nonetheless, catch data from Chilean whaling stations tells us that the female Chilean blue whale’s Lmean is 23.5 meters (4). Using ratios between L50/Lmean for other blue whale subspecies allowed researchers to estimate the L50 for Chilean blue whales to be 21.3 meters for females and 20.50 meters for males (14). The largest within the catch data are about 24.9-25.6 meters (4,14).

Lastly, we have the Northern blue whale. I wasn’t able to find any published articles that discussed the L50 and size of physical maturity like the Southern hemisphere whales. The only sources I have are books, which estimate the L50 to either be 21.65-23 meters or 22-22.6 meters (1,18). The latter source suggests that Northern blue whales physically mature at 23.2 meters and 24.7 meters for males and females, respectively. It’s hard to judge these approximations as I haven’t seen the methodology used to arrive at these lengths. At the same time, these lengths seem reasonable since the Northern hemisphere blue whale’s Lmean seems to be around 24.1 meters for females (1,19).

(2/21/2022 UPDATE: I have recently discovered relevant data for the size parameters of North Pacific Blue whales from the Fisheries Research Board of Canada. Maturity studies conducted on whales captured from 1949-1955, found that North Pacific Blue whales enter sexual maturity at about 69 feet for males and 71 feet for females (30,31). The length and weight tables will be updated for the Northern subspecies to reflect these findings. A bulletin reported that males and females physically mature at 78-80 feet and 80-85 feet, respectively. The upper-ranges seem too close to that of their Antarctic counterparts given the big difference of their respective L50 values. This becomes even more apparent when considering that whales in excess of 85 feet are rare in the catch records for the North Pacific. I was not able to locate the original source cited for these specific lengths. Therefore, the currently-listed sizes at physical maturity will remain the same, as they’re closer to what I’d estimated from the L(physical maturity)/ L50 ratio of Antarctic blue whales.)

While the average length for Northern blue whales may not seem so different from the Chilean subspecies, their maximum lengths are far greater. Within the whaling record, the largest North Pacific blue whales were females ranging from 26.8-27.1 meters and the largest in the North Atlantic was 28.1 meters (5,20). Mounted blue whale skeletons up to 26.5 meters from the North Pacific and 27 meters from the North Atlantic corroborate that those reported lengths were accurate figures. This is especially true given that the flesh of the intact specimens would extend slightly beyond the length of their skeletons. The largest ever reliably measured in the Northern Hemisphere was a 29.8-meter female that was shot down with machine guns for blocking the Panama Canal in January of 1922 (1,5,15,21). I was initially doubtful of this claim, however, an analysis of the whale’s cervical vertebra validated that the whale was measured accurately. However, its unusual size leaves me curious on whether this is truly of the Northern populations or if it’s some wayward Antarctic blue whale.

Blue whale graphic

Table 1

Subspecies	L₅₀ (meters)	L_mean (meters)	Length at physical maturity (meters)	Maximum length (meters)
Antarctic	22.6 (males) 23.4-23.7 (females)	24.3 (males) 25.6 (females)	25 (males) >26 (females)	32.64 (males) 33.27 (females)
Northern	21.0 (males) 21.6 (Females)	22.6* (males) 24.1 (females**)	23.2 (males)* 24.7 (females)*	~27.4 (males) 28.1 or 29.8 (females)
Pygmy/North Indian	18.6 (males) 19.2 (females)	20.3 (males) 21.0 (females)**	21.1 (males) 21.9 (females)	23.8 (males) 24.2 (females)
Chilean	20.50***(males) 21.3* (females)**	22.10 (males) 22.6-23.5 (females)	N/A (Likely similar to Northern subspecies)	23.4 (males) 24.9-25.6 (females)

Pygmy blue whale parameters updated from Branch’s work on earplug data (32)
*Uncertain methodology
**Approximated based on Lmean/L50 ratio for female pygmy blue whales
***Calculated value based on L50/Lmean ratios of other subspecies

Now as for the weight of these creatures, it’s a little tricky. While sources like Lockyer and Mikhalev provide regression formulae to approximate the weight of a blue whale, they’re derived from samples where the blue whales are of varying body conditions (6,9,22). Blue whales, while not exactly as strict seasonal feeders as other mysticetes, still consume food at a much greater rate during the summer feeding season. For Antarctic blue whales, this extends from November to March. By the beginning of the feeding season, blue whales are at their lean weight, and they gain about 50% of their body weight back by the end (6). Most of that weight gain is muscle, with fat being the next-largest contributing tissue. So as you can imagine, this drastic fluctuation in weight of an individual makes it difficult to accurately predict the weight of a blue whale with length alone. Luckily, Lockyer went through the extra step and aligned her sample of piecemeal weighings with their capture dates, allowing her to separate the ‘fatten’ and lean whales of the same lengths. This enabled her to create two linear graphs that relate a blue whale’s total weight (exclusive of body fluids) with its skeletal weight. In their lean state, blue whales weigh about 4.66 times their skeleton, while ‘fatten’ whales are about 6.94 times their skeletal weight.

Blue whale body condition graph — **Graph for masses and body condition for blue whales.**

At their L50 lengths, Antarctic blue whales range from 63-93 metric tons for males and 71-106 metric tons for females. For the Lmean , males and females range from 79-118 metric tons and 91-136 metric tons, respectively. At physical maturity, males vary from 86-128 metric tons and females at 97-144 metric tons. I’ll also report that at physical maturity, a male would average 102 metric tons while females average 117 over the course of the year.

Ichihara, the scientist who described the pygmy subspecies, realized that pygmy blue whales are heavier than ordinary blue whales at equal lengths (13). While the meat, blubber, and skeletal weights were even, the internal organs were about 53% heavier between a pygmy blue whale and a regular blue whale of 22 meters. This is because pygmy blue whales physically mature at a smaller size, and thus, have more developed organs than the Antarctic subspecies.

To accommodate pygmy blue whales, I used the viscera weight from the corresponding the life stage. So for a female pygmy blue whale at L50, rather than using the viscera weight of a blue whale at 19.2 meters, I use the viscera weight of an blue whale at 23.4 meters.

Table 2

Subspecies	Mass at L₅₀ (tonnes)	Mass of L_mean (tonnes)	Mass at physical maturity (tonnes)	Mass at maximum length (tonnes)
Antarctic	71-106 (females) 63-93 (males)	91-136 (females) 79-118 (males)	97-144 (females) 86-128 (males)	N/A (Likely exceeding 200)
Pygmy/North Indian	36-54 (females) 35-53* (males)	52-78 (females) 45-68 (males)	60-90 (females) 53-79 (males)	78-116 (females) 75-112 (males)
Chilean	50-75 (females) 42-63 (males)	67-99 (females) 58-86 (males)	N/A (Likely similar to Northern)	91-136 (females) 70-104 (males)
Northern	53-79 (females) 47-70 (males)	77-115 (females) 63-93 (males)	83-123 (females) 68-102 (males)	116-172 132-198* (females) 109-162 (males)

*based of skeletal weight of 6.40 tonnes from a 18.6 meter male pygmy blue whale
*Davis Strait whale
**Assuming skeleton of Panama whale is approx 26.8 metric tons.

This comparison is quite interesting to see. One thing I like is how even the pygmy blue whale by the end of the feeding season is still about as large as the largest sauropod species, with both sexes either approaching or surpassing 100 tonnes. You may notice that my estimates for the pygmy blue whale are smaller than what’s currently on Wikipedia. That’s because Wikipedia is using calculations from Lockyer’s regression for pygmy blue whales, which has a mere sample size of 5 that only ranges from about 16-21.8 meters and 20-70 tons. Naturally, it’s going to overestimate whales much greater than 23 meters, so I avoided using that formula.

What was the Biggest Blue Whale?

We’re now going to look at the record-breakers. The first one I want to get out of the way is the most recent size-record the blue whale broke: largest animal in fossil record.

In 2019, a fossilized skull of an anatomically-modern blue whale was recovered from Italy and is estimated to be about 1.37 million years old (23). The skull had a bizygomatic width of 294cm. When using formulae designed to reconstruct the length of fossil baleen whales, the estimated length ranged from 23.4-27.1 meters. However, estimations based off the known measurements of extant rorquals, including the blue whale, estimates it more consistently at 25.4-26.1 meters. This effectively means it was about the size of a physically-mature Antarctic blue whale and would easily average over 100 metric tons on the conservative end. No other fossil animal, even sauropods, approach a mass range such as that. I’m not sure how exactly this blue whale is related to modern populations, but if it’s a direct ancestor of the Northern subspecies, it’s on the relatively larger end.

Now, how big was the largest blue whale? There’s a debate concerning that as there’s reason to question the reliability of sources that were often cited in scientific literature. If you comb all the books and all the sources out there, you’re not going to quite get the same answer. Luckily, I did that for you and will provide a basic summary.

The canonically-cited largest blue whale was a female caught at Grytviken, South Georgia in 1909. This female measured 107 fot/Norwegian feet. This unit of measurement is actually slightly longer than an English foot (0.3138m vs 0.3048m), which meant the whale was 33.58 meters long (5,24,25,26). However, issues with whalers either misreporting the whale’s length, rounding, or using non-standard measuring techniques made certain experts wary of trusting the whaling record (2,4,5,10,25). Alternatively, some prefer to cite the largest blue whale measured directly by a scientist, which would be the 29.9-meter blue whale measured by Masaharu Nishiwaki in the 1946/1947 whaling season (18).

I generally choose to believe some of the whaling records, for specific reasons. The main reason is that while there has definitely been unreliability within catch length data from whaling records, the extent of falsification was contingent on the nationality of the whaling fleet, decade, and species (27,28). For example, catch-length data was heavily falsified for Japanese and Russian whaling fleets in the 1950s-1970s, especially for sperm whales. As far as issues with blue whales are concerned, it mainly applied to individuals that were below the minimum size quota enforced in 1937 (4,14,25). Individuals below the legal threshold of 21.3m were ”stretched” or reported as fin whales. This specific practice has never been shown to cause the ”stretching” of large blue whales, however, the opposite has been noted to occur. Ironically, whale-stretching involved shortening the reported length of larger sperm whales so that the catch length distributions stayed consistent with production yields.

There are also concerns on whalers not using the zoological standard for measuring whales, which has been observed (1,4,15). For this reason, I cautiously disregard the 33.58-meter whale, since not much is documented about how it was measured. Sigurd Risting also published that two whales were killed in March 1926 in South Shetlands: a 106 fot/33.26 meter female and a 104-fot/ 32.64 meter male (1,5,6,26). The largest whales were quite rare, as only 5 whales out of the entire sample exceeded 100 fot/31.4-meters.

Even when accounting for the lack of precision for individuals measured during the 1920s , it’s very likely that at least some of the largest whales recorded from the 1930/31 season onward were accurately measured. Of these whales, the largest has been recorded to reach up to 31.1m in length. All of these whales were from the Southern Hemisphere and none of the other regions show records beyond their scientifically-recognized maximums.

The largest sample directly measured by scientists were by the Discovery Committee, which only ranged up to 28.5 meters for females and 26.5 meters for males (5,10,15). This led some experts to doubt Risting’s data. The Discovery Committee’s sample was certainly sufficient for illustrating how blue whales over 28-meters are exceptional, but even Nishiwaki’s 29.9m specimen shows that the Discovery’s measurements shouldn’t be strictly-adhered to when assessing the maximum sizes for Antarctic blue whales.

In my opinion, whaling data became more accurate after the early 1930s, where the largest whales consistently measured between 100-102 ft.

The Heaviest Blue whale to be weighed

Now as for the largest whales ever weighed, you may have read about 3 figures thrown around a lot for the blue whale’s maximum weight: 150 tons, 180 metric tons, and 190 metric tons. While there’s not as much debate regarding the validity of weighings as there is for reported lengths, I do occasionally see literature switching between each of these figures as the most valid estimate. I’m going to explain the sources behind each figure.

The most common one I’ve seen was a 27.1-meter whale measured by Japanese whalers and documented by Lt. Col. Waldon C Winston on January 27, 1948 (1,5,6, 11,18,22,26,28). This whale weighed 127.5 metric tons exclusive of body fluids, with 136.4 tonnes/ 150 short tons being the final tally when accounting for the lost fluids composing 6.5% of the intact body weight. Winston provided a complete tabulation of the whale’s tissue content towards the total weight. This figure was highly favorable to scientific sources (29). The skeleton weighed 18.59 tonnes, meaning the total-weight: bone-weight ratio was 6.86. This whale was very well fed as it was approaching its maximum mass for the austral summer. This figure, however, falls short for providing a reference of the largest blue whale as it was nowhere near the maximum length.

The 180-tonne whale is probably the most obscure of the three. This specimen was a 29.5-meter blue whale taken in by the Messrs Southern Whaling and Sealing Company and was weighed by chemist R. Squire in 1931 (12,24). Instead of small scales, this whale was weighed from pressure cookers. The whale was originally reported to have a piecemeal weight of 163.7 short tons and a complete weight of 174 short tons when accounting for fluid loss. However, Victor B. Scheffer, when calculating the total weight, mentioned there was an error in the reporting. Scheffer cites that the whale actually weighed 163.7 imperial long tons, which are actually heavier than metric tons. This meant the whale weighed about 178 metric tons/ 196 short tons while alive. However, I have noticed one source incorrectly state the whale was 196 long tons/ 199 metric tons (24,25). This unfortunately carried over to Wikipedia. This was the longest whale to have its weight reported, but not the heaviest.

The 190-metric ton blue whale was a 27.6-meter blue whale that was caught by the Soviet whaleship, Slava, on March 20, 1947 (1,5,22,26). I generally see this source cited a lot, and not many contest it. Nonetheless, I do see why some find it questionable. This whale only has about two-thirds of the tissue weight accounted for. All we have is 26 tonnes for the skeleton, 30 for the blubber, 66 for the flesh, 4.3 for the tongue, 0.98 for the liver, 0.7 for the heart, and 1.4 for the lungs. That’s about 129 metric tons for the individual tissue types.

It seems that the blubber was only partially reported for this specimen as 30 tonnes would be far too low given the whale’s reported diameter of 4-meters and maximum blubber thickness at 42cm, which exceeds the range reported near the dorsal fin in other literature. This directly indicates that the whale was of exceptional condition. Authors defined ”blubber” inconsistently, in this case it can be easily assumed the 30 tonnes refers only to the blubber found along the flanks and body, which comprises about 40-44% of the pooled weight of all blubber tissue.

Scaled from a 25.3m/83-foot pregnant female (6) would predict a blubber weight of 57.4 tonnes, but it’s unlikely to be in the same exceptional condition as Voronin’s. Using percentages I provide about would suggest that pooled blubber weight for Voronin’s whale was about 70 tonnes. Since the GI tract and visceral fat would realistically amount to another 10 tonnes, that places the weight to about 180 tonnes without corrections for other organs, the baleen , and estimated blood.

Estimated Tabulation of Slava’s 190-tonne Whale

Component	Mass (tonnes)
Skeleton	26.00
Muscle	66.00
Blubber Total	70
Internal Organs	23.68
Heart	0.7
Lungs	1.40
Tongue	4.30
Liver	0.98
GI-Tract (Stomach+Intestines) & Visceral fat	10.0
Total	180

While this whale may seem unusually heavy for its length, like I mentioned before, there can be a lot of heterogeneity in the individual morphology of blue whales. Multiple sources recognize the largest oil yield from a blue whale to have come from a 27.7-meter whale caught on Walvis Bay, South Africa on July 13th, 1924 (1,5,10,15,16) . This whale yielded about 305 barrels of oil, which would weigh roughly 50 metric tons. Considering how the oil yield typically accounts for about 24% of the whale’s body weight (6), this likely meant the whale would’ve conservatively weighed similarly to the whale caught by the Slava. However, blue whales of this weight are more likely to be around 30 meters long.

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References

1.Tomilin, A. G. 1957. Cetacea. Mammals of the U.S.S.R. and adjacent countries. Volume 9. Akademii Nauk SSSR, Moskow (translated by the Israel Program for Scientific Translations, Jerusalem, 1967, 717 pp.).

2. Bortolotti, D. (2008). Wild Blue: A Natural History of the World’s Largest Animal. New York: St. Martin’s Press.

3.Carwardine, M. (202o). The Handbook of Whales, Dolphins and Porpoises of the World. Princeton, New Jersey: Princeton University Press.

4.Branch, T., Abubaker, E., Mkango, S., & Butterworth, D. (2007). Separating southern blue whale subspecies based on length frequencies of sexually mature females. Marine Mammal Science, 23, 803–833. https://doi.org/10.1111/j.1748-7692.2007.00137.x

5.Wood, G. L. (1976). The Guinness book of animal facts and feats. United Kingdom: Guinness Superlatives.

6.Lockyer, Christina & FAO, Rome & FI, & Mammals, Advisory & (Norway, Bergen & Aug,. (1981). Growth and energy budgets of large baleen whales from the southern hemisphere. FAO Fisheries Series. 5. 379-487.

7. Gambell, R. 1970. Weight of a sperm whale, whole and in parts.

8. Boschma, H. 1938. On the teeth and some other particulars of the sperm whale (Physeter macrocephalus L.). –– Temminckia 3: 151––278.

9. Mikhalev, Y. (2019). Whales of the Southern Ocean: Biology, Whaling and Perspectives of Population Recovery. Springer International Publishing. https://doi.org/10.1007/978-3-030-29252-2

10.Scheffer, V. B. (1974). The largest whale. Defend. Wildl. Int. 49(4), 272-274.

11. Waldon C. Winston, “The Largest Whale Ever Weighed,” Natural History Magazine, 1950.

12. Laurie, A. H., “Some Aspects of Respiration in Blue and Fin Whales”, Discovery Reports, 7, 363–406, 1933

13. Ichihara, T. (1966). “The pygmy blue whale, “Balaenoptera musculus brevicauda”, a new subspecies from the Antarctic”. In Norris, K. S. (ed.). Whales, Dolphins and Porpoises. Berkeley, CA: University of California Press. pp. 79–113.

14. Pastene, L. A., Acevedo, J., & Branch, T. A. (2020). Morphometric analysis of Chilean blue whales and implications for their taxonomy. Marine Mammal Science, 36(1), 116–135. https://doi.org/10.1111/mms.12625

15. Mackintosh, N. A., & Wheeler, J. F. G. (1929). Southern Blue and Fin Whales. Discovery Reports, 1, 257–540.

16. S. Risting, “Whales and Whale Foetuses: Statistics of Catch and Measurements Collected from the Norwegian Whalers’ Association 1922–1925,” Rapports et Procès-Verbaux des Réunions 50 (1928): 1–122.

17. Branch, T. A., & Mikhalev, Y. A. (2008). Regional differences in length at sexual maturity for female blue whales based on recovered Soviet whaling data. Marine Mammal Science, 24(3), 690–703. https://doi.org/10.1111/j.1748-7692.2008.00214.x

18. Marine Mammals of Eastern North Pacific and Arctic Waters. (1986). United States: Pacific Search Press.

19.Gilpatrick, J., & Perryman, W. (2008). Geographic variation in external morphology of North Pacific and Southern Hemisphere blue whales (Balaenoptera musculus). Journal of Cetacean Research and Management, 10.

20.Reeves, R., Clapham, P., Brownell, R., & Silber, G. (1998). Recovery Plan for The Blue Whale (Balaenoptera musculus).

21. Harmer, S. F. (1923). 55. Cervical Vertebrae of a Gigantic Blue Whale from Panama. Proceedings of the Zoological Society of London, 1923, 1085–1089. https://doi.org/10.1111/j.1096-3642.1923.tb02223.x

22. Lockyer, Christina. (1976). Body weight of some species of large whales. Ices Journal of Marine Science – ICES J MAR SCI. 36. 259-273. 10.1093/icesjms/36.3.259

23. Bianucci, G., Marx, F. G., Collareta, A., Di Stefano, A., Landini, W., Morigi, C., & Varola, A. (2019). Rise of the titans: Baleen whales became giants earlier than thought. Biology Letters, 15(5), 20190175. https://doi.org/10.1098/rsbl.2019.0175

24.Carwardine (1995) Carwardine M. The guinness book of animal records. Middlesex, UK: Guinness Publications; 1995.

25. McClain, C. R., Balk, M. A., Benfield, M. C., Branch, T. A., Chen, C., Cosgrove, J., Dove, A. D. M., Gaskins, L., Helm, R. R., Hochberg, F. G., Lee, F. B., Marshall, A., McMurray, S. E., Schanche, C., Stone, S. N., & Thaler, A. D. (2015). Sizing ocean giants: Patterns of intraspecific size variation in marine megafauna. PeerJ, 3, e715. https://doi.org/10.7717/peerj.715

26. Ridgway Sam H., Harrison Richard J. (Eds.) Handbook of Marine Mammals. Volume III. The Sirenians and Baleen Whales [PDF]—All for the student. (n.d.). Retrieved October 3, 2021, from https://www.twirpx.com/file/2582614/

27. Clapham, P. J., & Ivashchenko, Y. V. (n.d.). Stretching the truth: Length data highlight falsification of Japanese sperm whale catch statistics in the Southern Hemisphere. Royal Society Open Science, 3(9), 160506. https://doi.org/10.1098/rsos.160506

28. Ivashchenko, Y. V., Clapham, P. J., & Brownell, R. L. (n.d.). Soviet Illegal Whaling: The Devil and the Details. Marine Fisheries Review, 19.

29. Spying on Whales by Nick Pyenson: 9780735224582 | PenguinRandomHouse.com: Books. (n.d.). Retrieved October 3, 2021, from https://www.penguinrandomhouse.com/books/556686/spying-on-whales-by-nick-pyenson/

30. Pike, G. C, and MacAskie, I. B. (1969). Marine mammals of British Columbia. Fish. Res. Board Can. Bull. 171, 1-54.

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32. Branch, T. (2014). Biological parameters for pygmy blue whales.

The smallest within the largest: How host phylogeny and diet influence whale gut microbiomes.

Whales prove to be a very interesting and unique clade of mammals from many angles, be it their evolution towards fully-aquatic lives, feeding strategies, gigantism, sensory adaptations, or cognitive abilities. Now as the study of microbiomes adds new dimensions to understanding animals, whales continue to stick out.

Quick intro to microbiomes

I should provide a crash-course for those not too keen on microbiology before heading into the crux of this post. A microbiome is the collection of microorganisms or the total amount of microbial genetic material in an environment. Not only are microbiomes defined in environments like soil and bodies of water but also within multicellular hosts like plants and animals. Microbiomes are often defined on the skin, respiratory tracts, blood, and digestive tracts of humans and animals. Microbiomes can be vital because they often regulate the health of the host species they inhabit. These roles can vary from aiding digestion or out-competing invading pathogens for resources. Research into characterizing microbiomes in humans and other species is a relatively recent practice compared to other fields such as anatomy, behavior, and genetics. We’re now learning that this overlooked character is extremely important.

When assessing microbiomes, we use similar metrics discussed in ecology: richness, eveness, and function . Richness is simply the number of species present in an environment. Eveness is the relative abundance of each species, and this value can be combined with richness to calculate the diversity within a microbiome. Function includes a microbe’s niche, typically the type of molecules they break down. Diversity and function are measured by collecting samples from the microbiome (methodology varies with the environment being sampled), extracting the DNA/RNA from the microbiomes, amplifying desired sequences, sequencing the genetic material and aligning the informative regions to reveal the identity of species present. There’s a lot more to the process such as filtering out contamination, separating high and low-quality sequences, etc. With the resulting data, the taxonomic composition of a microbiome becomes available. Functional profiles are provided by measuring the expression of specific genes within the samples. The results of these procedures can vary depending on the precise methodology and equipment used.

When characterizing a host species’ microbiome, we look for core assemblages, which are the bacterial taxa that are mutually shared between the majority or the entirety of the population. Core assemblages are important to define for host species, as deviations from the core assemblage of a species or population can infer a major health risk. Therefore, microbiome samples should be a priority for conservation research.

This post will focus on the gut microbiomes, which are most often analyzed from fecal samples. A key concept about the gut microbiome is that it’s often controlled by diet, as the type food the host consumes provides the nutrients available to the bacteria. Another component is the evolutionary history of the host. Host phylogeny matters because the anatomy and physiology of the GI-tract is the literal environment in which the bacteria must thrive. The consequence of this is what’s known as phyolgenetic intertia, the retention of the ancestral gut microbiome even after adapting to a unique diet. A classic example is the giant panda, which lacks a microbiome that’s enriched with the bacteria typical of other herbivores. Instead, the giant panda’s microbiome clusters with other ursids and carnivores (1). This is because the panda’s GI-tract is simple and lacks the multi-chambered adaptations present in ruminants, horses, and rabbits. Pandas are still ”carnivores” with respect to their digestive anatomy. Since both anatomy and diet shape the host’s hospitability for microbes, gut microbiomes can change within the same host over the course of time or across different sections of the GI-tract.

The gut microbiomes of cetaceans

Now to finally bring this conversation back to whales. Those who are familiar with their evolutionary history, as discussed in my Cetology 101 article, can see where I am going. Whales are strict carnivores, but since they are deeply-nested within artiodactyls, their terrestrial ancestors were herbivores at some point. Therefore, whales occupy an extremely interesting dietary niche with respect to their phylogeny. This is especially true in the case of baleen whales. Baleen whales consume crustaceans like euphausiids (krill), copepods, amphipods, mysids, etc. The exoskeletons of these animals are composed of chitin, which is a structural polysaccharide (long-chained sugar) like the cellulose consumed by herbivores. Chitin and cellulose are both composed of chains of glucose, like starch. However, the bonds linking the glucose molecules in chitin and cellulose are much stronger, making these molecules harder to digest than starch.

Ruminants break down cellulose with the aid of the microbiome within their forestomach. The upper digestive tract of ruminants has 4 chambers: the rumen, reticulum, and omasum, and abomasum. Of these, only the abomasum is the true homolog to the stomach, the rest are derived from the esophagus. The rumen and reticulum house microbes that are capable of breaking down cellulose and the omasum passes food particles to be digested in the abomasum. This process is known as foregut fermentation. Cetaceans also possess a forestomach, however this structure is not believed to be homologous to the pregastric chambers of ruminants as the cetacean forestomach is derived from the true stomach. Nonetheless, this structure was likely an analogous fermentation chamber of cellulose in the ancestors of whales that may have been converted to do the same for chitin. Preliminary evidence for this hypothesis was the detection of high concentrations of short-chained fatty acids (SCFA’s) in the forestomaches of baleen whales (2). SCFA’s, for the purpose of this discussion, are products from the fermentation of carbon sources.

(Click on caption of diagram below for full description)

The anatomy of the upper digestive tract of most cetaceans (left) and ruminants (right). Arrows are provided to reveal path of food throughout ruminant’s esophageal chambers. E=esophagus; F= Forestomach; M= Main stomach; C=Connecting channel; P=Pyloric chamber; DA= Duodenal Ampullae; HPD=Hepatopancreatic duct; RU=Rumen; RT= Reticulum; O= Omasum; AB=Abomasum. The rumen and reticulum are the fermentation chambers for ruminants while the forestomach is the proposed site for cetaceans.

As mammalian carnivores that possess anatomically-herbivorous digestive tracts, the gut microbiome of cetaceans present a unique opportunity to understand how diet and phylogeny interact. This is not mirrored by any other marine mammal, as Sirenians and Pinnipeds both occupy dietary niches that align with their ancestral digestive anatomy. Work has been done into cetacean microbiomes over the past half decade, but the science remains immature. Nonetheless, I will provide the basic summary of what we currently know.

In 2015, researchers conducted a taxonomic and functional comparison between the fecal microbiomes baleen whales and terrestrial mammals. They concluded that the microbiomes of baleen whales were very unique, possessing qualities of both carnivores and herbivores. At the phylum-level, the fecal microbiomes of baleen whales were very similar to those of terrestrial mammals, dominated by Bacteroidetes and Firmicutes (2). Bacteroidetes and Firmicutes make up the majority of the gut microbiome in most mammals, including humans. However, whales still had some enrichments in bacterial phyla that were uncommon in terrestrial mammals (Spirochaetes). At the species-level, the similarities with terrestrial mammals decreased greatly.

Functionally, the fecal microbiomes of baleen whales were similar to carnivores for genes related to digesting and synthesizing proteins. However, baleen whales and herbivores were much closer for genes involved in carbon and lipid metabolism. Baleen whales grouped independently from both terrestrial carnivores and herbivores for carbohydrate metabolism. This meant that whales and herbivores broke down sugars differently (which is to be expected because chitin and cellulose are different sugars), but all the downstream steps for breaking down the lower-level carbon molecules were the same. This is consistent with the hypothesis of chitin-fermentation.

Another notable finding were the carbohydrate-active enzymes (CAZymes) profiles for the microbiomes of baleen whales. CAZymes are genes involved in the digestion of carbohydrates. The CAZy profiles of the baleen whale microbiomes were unique from those of terrestrial mammals (2). Baleen whales even lacked affinity with insectivores, whose prey also possess chitinous exoskeletons. Despite feeding on insects, insectivore gut microbiomes were not enriched in genes related to chitin-digestion when compared to the average carnivore. Baleen whales, however, were particularly enriched in these very genes. Like in the situation of the panda, this pattern is likely due to the insectivores having simple digestive anatomy, while whales inherited a forestomach capable of housing chitin-fermenting bacteria.

The microbiome analyses firmly support that baleen whales engage in the foregut fermentation of chitin, paralleling their ruminant relatives. Dolphins and porpoises on the other hand, clustered with other marine piscivores. Studies of the fecal microbiomes of the bottlenose dolphin, striped dolphin, and East Asian finless porpoise were all found to be largely enriched by the bacterial phyla Firmicutes and Proteobacteria (3,4,5,6). The lineages within Proteobacteria were related to those found in piscivorous marine fish, indicating a convergence from their shared dietary niche (7). Belugas were somewhat different, as their microbiomes were enriched in Actinobacteria. This is odd, as belugas belong to a sister clade to porpoises and share a similar diet. Differences in their environments might be the key here. Porpoises and dolphins generally live in lower latitudes, while belugas live in Arctic and subarctic waters. This explanation is supported by the gut microbiome of the hooded seal, which had a far greater relative abundance of Actinobacteria relative to Proteobacteria (8). As of yet, precise functional profiles for toothed whales are not as extensive as they are for baleen whales.

It seems that, in general, toothed whales overcame their phylogenetic inertia and aligned with piscivores, right? Well, this is where sperm whales come in to make this whole thing weird. The taxonomic profiles of the true, pygmy, and dwarf sperm whales revealed their microbiomes cluster much more closely to baleen whales than to other toothed whales. Like baleen whales, Bacteroidetes and Firmicutes were the dominant phyla in all three sperm whale species, but the Kogiids’ microbiomes were distinct from baleen whales for lower-abundance phyla (9,10,11,12). No significant differences were found between the fecal microbiomes of baleen whales and the sperm whale (Physeter macrocephalus) at the phylum-level, only at the family/genus-level (12). Furthermore, some of the lineages detected in Kogiids were associated with fermentation, which is consistent with previous analyses of the bile acid in sperm whales (9).

I think these preliminary similarities between baleen whales and sperm whales are striking when taking into consideration of their phylogeny. Baleen whales and toothed whales diverged about 36-37 million years ago, while sperm whales diverged from other odontocetes 32-35 million years ago (13, figure below). So while sperm whales are more closely related to dolphins and belugas than they are to baleen whales, the sperm whales’ ancestors were a very basal odontocete lineage. While the precise phylogeny of fossil physeteroids has yet to be fully resolved, it may be possible that the ancestor of the teuthivorous sperm whales had similarities to the ancestors of mysticetes. This may be possible, as early mysticetes are believed to have been suction-feeders, much like sperm whales (14).

(Click on caption of diagram below for full description)

Time-calibrated phylogenetic tree of host taxa along with dominant phyla residing in fecal microbiome communities.

But their phylogeny still fails to answer precisely why the fecal microbiomes between modern sperm whales and baleen whales are so similar. Is it some anatomical similarity between these clades, or is there something we’ve overlooked regarding their diets? I believe it’s definitely worth noticing that the pens and beaks of squids are composed of chitin. This idea may seem counterintuitive for some sperm whale experts, as the beaks and pens of squid are often recovered undigested. However, it’s too distracting that the gut microbiomes of sperm whales, who feed on chitin-rich prey, cluster more closely to a group whose microbiomes are geared towards chitin. A supporting detail is that one isolate from the Kogiid fecal microbiome showed visible utilization of chitin (10). This may hint at some weak chitin digestion in sperm whales. If not necessarily for nutritional purposes, it may serve as a defense mechanism to protect the GI-tract, like ambergris. More research in the functional profiles of sperm whale microbiomes is necessarily to make sense of all of this.

So in general, we see the following trend across cetaceans. Baleen whales and sperm whales have microbiomes that share taxonomic affinities with terrestrial herbivores and are functionally skewed towards fermentation. Other odontocetes such as dolphins, porpoises, and belugas have microbiomes convergent with typical marine piscivores. Until more information is acquired, the shared exposure to chitin-rich prey seems to explain the fecal microbiome homology between baleen whales and sperm whales .

(Click on caption of diagram below for full description)

Schematic detailing how baleen whales and sperm whales both feed on chitin rich prey and share fecal microbiomes enriched with Bacteroidetes and Firmicutes. Fish-eating dolphins, by contrast, possess fecal microbiomes more enriched in Proteobacteria.

Limitations of current research

Even though we’ve learned a lot so far in the past half-decade, there’s still so many gaps to fill regarding cetacean gut microbiomes. I’d say the biggest shortcoming of the existing research is the taxon sampling. Every cetacean species with published gut microbiome data is present within my bibliography (this article is based on a literature review I’ve done for my microbiology class). Among these, not a single beaked whale has been sampled, which is problematic.

The beaked whales’ inclusion is very necessary in the discussion of phylogenetic inertia’s role in cetacean gut microbiomes due to unique features of their anatomy. In accordance to their general weirdness, beaked whales lack forestomaches (15)! It should be of great interest to obtain a fecal sample of the beaked whales and observe how their gut microbiomes align or deviate from other cetaceans. Specifically, they ought to be compared with sperm whales, as they share the closest dietary niches. Accordingly, we should also prioritize sampling the polyphyletic clades of river dolphins, as the Yangtze river dolphin and the La Plata dolphin also lack forestomaches (16). While the former is extinct, sampling of the La Plata dolphin may still yield information to make reasonable speculations.

Aside from the absence of beaked whales from the datasets, more analyses are needed from the currently-sampled species. The existing datasets for the gut microbiomes of toothed whales only includes taxonomic compositions . Preliminary functional profiles have only been obtained for baleen whale microbiomes. Furthermore, most species have only been surveyed through fecal samples. These can only provide a snapshot of the composition of the gut microbiome, and cannot properly elucidate how it’s structured throughout the different sections of the GI-tract. The gut microbiome of the esophagus and stomach can look very different from the colon. Indeed significant changes in taxonomic composition has been observed throughout the GI-tracts and life histories of the bottlenose dolphins, finless porpoises, kogiids, and bowhead whales (4,6, 10, 17).

Attention should also be paid towards the health and residency status of the specimen being sampled. Diseases or antibiotic treatments are liable to disturb the taxonomic composition of gut microbiomes collected from stranded specimens (18). As for residency status, researchers should avoid over-reliance on data collected from captive individuals, as major differences in core assemblages were found in wild vs captive comparisons (19).

All of these measures ought to be considered for any future research, as adherence will allow for stronger data that will make way for clearer patterns.

The bigger picture

I have established the gut microbiome’s importance within their hosts, but not at any greater scale. To gain perspective of how gut microbiomes ultimately affect the world at large, we must tie them back to how whales regulate the environment.

The ocean stores about 50 times as much CO2 as the atmosphere and absorbs around one-third of the carbon emitted by humans (20). There are multiple means the ocean removes CO2 from the air, but one of the major means is the biological pump. Basically, the biological pump describes how the primary producers like cyanobacteria and algae fix CO2 from the atmosphere and convert the carbon into organic matter. This organic matter is then stored into the bodies of the marine animals at higher trophic levels. When these animals die, their bodies sink to the bottom of the oceans and the carbon is stored into the ocean interior. Large vertebrates with few predators such as baleen and sperm whales play a very important role in the biological pump of the ocean. Larger animals require less food per unit of mass as smaller animals, meaning they are more efficient for storing carbon in the water (21). This means that if the Antarctic blue whales went extinct, the increase in biomass of Adélie penguins and minke whales in response to the new krill availability would only be a fraction of the lost blue whale biomass. We cannot count on an increase of smaller species to replace the carbon storage a larger animal once provided.

With this background of the biological pump in mind, the decimation of large cetacean populations from whaling should become very troubling. A study has calculated that the current populations of 8 species of large baleen whales (Blue, fin, humpback, gray, sei/Bryde’s, right, bowhead, and minke) are storing about 9.1 million less metric tons of carbon than during the pre-whaling era (21). If these populations were to be rebuilt to to their historical abundances, the oceans could store 8.7 million more metric tons of carbon. Furthermore, the carcasses from ”whale falls” is expected to allow the ocean to remove 160,000 more metric tons of carbon per year. While this may seem small compared to the total carbon sink of the ocean, restoring whale and fish populations is very comparable to other management projects, such as iron fertilization.

In addition to just storing carbon in their bodies, whales also support the oceans by guiding the cycling of nutrients. As whales return from deep-water foraging, they provide nitrogen and iron to phytoplankton when defecating at the surface (22,23). Furthermore, baleen whales transport nitrogen from nutrient-rich high-latitudes to nutrient-poor low-latitudes as they defecate along the migratory paths (24). Through these processes, whales act as both horizontal and vertical vectors of nutrients for primary producers of the ocean. Their carcasses also provide nutrients to scavengers at the surface and even full-on habitats for decomposers at the sea floor (25).

How does all of this relate back to gut microbiomes? Well, as mentioned before, these microbes are what allow a baleen whale to efficiently digest abundant carbon sources in the ocean such as chitin and a class of lipid known as wax esters. Like chitin, wax esters comprise a large proportion of the carbon in the ocean and is very difficult to digest for the majority of vertebrates. Whales and seabirds are the only vertebrates that showed high efficiency in digesting wax esters. The concentration of wax esters throughout the GI-tract of bowhead whales was shown to vary greatly with changes in the composition of the gut microbiome (17). Therefore, it’s very likely the gut microbiome plays a similar role in processing wax esters as they do with chitin.

All of the processes in which whales help manage the oceans are dependent on their ability to properly acquire energy and nutrients from their prey. Indeed, it is the smallest organisms that enable the largest animals to be major drivers of the biogeochemical cycling of carbon and nutrients of the ocean. Just as in other biological concepts, superlative nature of whales strongly illustrates the importance of microbiomes.

I hope this article proved interesting for readers despite possibly being my most technical paper as of yet. This article is basically a huge paraphrasing of two papers I’ve done for my senior year of undergrad. I really loved covering this topic for both semesters and I ended up learning so much. One of these papers was a literature review, and I pretty much copied that entire bibliography for this paper. So if you want to learn everything there is to know about the gut microbiome of cetaceans at this point in time, the sources below will essentially cover it with the addition of the following study (26).

Xue, Z., Zhang, W., Wang, L., Hou, R., Zhang, M., Fei, L., Zhang, X., Huang, H., Bridgewater, L. C., Jiang, Y., Jiang, C., Zhao, L., Pang, X., & Zhang, Z. (2015). The bamboo-eating giant panda harbors a carnivore-like gut microbiota, with excessive seasonal variations. MBio, 6(3), e00022-00015. https://doi.org/10.1128/mBio.00022-15
Sanders, J. G., Beichman, A. C., Roman, J., Scott, J. J., Emerson, D., McCarthy, J. J., & Girguis, P. R. (2015). Baleen whales host a unique gut microbiome with similarities to both carnivores and herbivores. Nature Communications, 6(1), 8285. https://doi.org/10.1038/ncomms9285
Morris, P. J., Johnson, W. R., Pisani, J., Bossart, G. D., Adams, J., Reif, J. S., & Fair, P. A. (2011). Isolation of culturable microorganisms from free-ranging bottlenose dolphins (Tursiops truncatus) from the southeastern United States. Veterinary Microbiology, 148(2), 440–447. https://doi.org/10.1016/j.vetmic.2010.08.025
Godoy-Vitorino, F., Rodriguez-Hilario, A., Alves, A. L., Gonçalves, F., Cabrera-Colon, B., Mesquita, C. S., Soares-Castro, P., Ferreira, M., Marçalo, A., Vingada, J., Eira, C., & Santos, P. M. (2017). The microbiome of a striped dolphin (Stenella coeruleoalba) stranded in Portugal. Research in Microbiology, 168(1), 85–93. https://doi.org/10.1016/j.resmic.2016.08.004
Abdelrhman, K. F. A., Ciofini, A., Bacci, G., Mancusi, C., Mengoni, A., & Ugolini, A. (2020). Exploring the resident gut microbiota of stranded odontocetes: High similarities between two dolphin species Tursiops truncatus and Stenella coeruleoalba. Journal of the Marine Biological Association of the United Kingdom, 100(7), 1181–1188. https://doi.org/10.1017/S0025315420000983
Wan, X.-L., McLaughlin, R. W., Zheng, J.-S., Hao, Y.-J., Fan, F., Tian, R.-M., & Wang, D. (2018). Microbial communities in different regions of the gastrointestinal tract in East Asian finless porpoises (Neophocaena asiaeorientalis sunameri). Scientific Reports, 8(1), 14142. https://doi.org/10.1038/s41598-018-32512-0
Huang, Q., Sham, R., Deng, Y., Mao, Y., Wang, C., Zhang, T., & Leung, K. (2020). Diversity of gut microbiomes in marine fishes is shaped by host‐related factors. Molecular Ecology, 29. https://doi.org/10.1111/mec.15699
Acquarone, M., Salgado-Flores, A., & Sundset, M. A. (2020). The Bacterial Microbiome in the Small Intestine of Hooded Seals (Cystophora cristata). Microorganisms, 8(11). https://doi.org/10.3390/microorganisms8111664
Erwin, P. M., Rhodes, R. G., Kiser, K. B., Keenan-Bateman, T. F., McLellan, W. A., & Pabst, D. A. (2017). High diversity and unique composition of gut microbiomes in pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales. Scientific Reports, 7. https://doi.org/10.1038/s41598-017-07425-z
Denison, E. R., Rhodes, R. G., McLellan, W. A., Pabst, D. A., & Erwin, P. M. (2020). Host phylogeny and life history stage shape the gut microbiome in dwarf ( Kogia sima ) and pygmy ( Kogia breviceps ) sperm whales. Scientific Reports, 10(1), 15162. https://doi.org/10.1038/s41598-020-72032-4
Li, C., Tan, X., Bai, J., Xu, Q., Liu, S., Guo, W., Yu, C., Fan, G., Lu, Y., Zhang, H., Yang, H., Chen, J., & Liu, X. (2019). A survey of the sperm whale (Physeter catodon) commensal microbiome. PeerJ, 7. https://doi.org/10.7717/peerj.7257
Glaeser, S. P., Silva, L. M. R., Prieto, R., Silva, M. A., Franco, A., Kämpfer, P., Hermosilla, C., Taubert, A., & Eisenberg, T. (2021). A Preliminary Comparison on Faecal Microbiomes of Free-Ranging Large Baleen (Balaenoptera musculus, B. physaus, B. borealis) and Toothed (Physeter macrocephalus) Whales. Microbial Ecology. https://doi.org/10.1007/s00248-021-01729-4
Zurano, J. P., Magalhães, F. M., Asato, A. E., Silva, G., Bidau, C. J., Mesquita, D. O., & Costa, G. C. (2019). Cetartiodactyla: Updating a time-calibrated molecular phylogeny. Molecular Phylogenetics and Evolution, 133, 256–262. https://doi.org/10.1016/j.ympev.2018.12.015
Lambert, O., Martínez-Cáceres, M., Bianucci, G., Celma, C. D., Salas-Gismondi, R., Steurbaut, E., Urbina, M., & Muizon, C. de. (2017). Earliest Mysticete from the Late Eocene of Peru Sheds New Light on the Origin of Baleen Whales. Current Biology, 27(10), 1535-1541.e2. https://doi.org/10.1016/j.cub.2017.04.026
Mead, J. G. (2007). Stomach anatomy and use in defining systemic relationships of the cetacean family ziphiidae (beaked whales). The Anatomical Record, 290(6), 581–595. https://doi.org/10.1002/ar.20536
Yamasaki, F., & Kamiya, T. (2017). THE STOMACH OF THE BOUTU , INIA GEOFFRENSIS: COMPARISON WITH THOSE OF OTHER PLATANISTIDS. https://www.semanticscholar.org/paper/THE-STOMACH-OF-THE-BOUTU-%2C-INIA-GEOFFRENSIS-%3A-WITH-Yamasaki-Kamiya/7d13b25aa7080324fcbb617a33600d61c5017081
Coordinated transformation of the gut microbiome and lipidome of bowhead whales provides novel insights into digestion | The ISME Journal. (n.d.). Retrieved October 26, 2020, from https://www.nature.com/articles/s41396-019-0549-y#Sec10
Bai, S., Zhang, P., Lin, M., Lin, W., Yang, Z., & Li, S. (2021). Microbial diversity and structure in the gastrointestinal tracts of two stranded short-finned pilot whales (Globicephala macrorhynchus) and a pygmy sperm whale (Kogia breviceps). Integrative Zoology, 16(3), 324–335. https://doi.org/10.1111/1749-4877.12502
Captive environment influences the composition and diversity of fecal microbiota in Indo‐Pacific bottlenose dolphins, Tursiops aduncus. (n.d.). https://doi.org/10.1111/mms.12736
Rackley, S. A. (2010). Chapter 12—Ocean Storage. In S. A. Rackley (Ed.), Carbon Capture and Storage (pp. 267–286). Butterworth-Heinemann. https://doi.org/10.1016/B978-1-85617-636-1.00012-2
Pershing, A. J., Christensen, L. B., Record, N. R., Sherwood, G. D., & Stetson, P. B. (2010). The Impact of Whaling on the Ocean Carbon Cycle: Why Bigger Was Better. PLoS ONE, 5(8), e12444. https://doi.org/10.1371/journal.pone.0012444
Lavery, T. J., Roudnew, B., Gill, P., Seymour, J., Seuront, L., Johnson, G., Mitchell, J. G., & Smetacek, V. (2010). Iron defecation by sperm whales stimulates carbon export in the Southern Ocean. Proceedings of the Royal Society B: Biological Sciences, 277(1699), 3527–3531. https://doi.org/10.1098/rspb.2010.0863
Roman, J., & McCarthy, J. J. (2010). The Whale Pump: Marine Mammals Enhance Primary Productivity in a Coastal Basin. PLOS ONE, 5(10), e13255. https://doi.org/10.1371/journal.pone.0013255
Roman, J., Estes, J., Morissette, L., Smith, C., Costa, D., McCarthy, J., Nation, J., Nicol, S., Pershing, A., & Smetacek, V. (2014). Whales as marine ecosystem

engineers. Frontiers in Ecology and the Environment, 12.

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Smith, C. R., Glover, A., Treude, T., Higgs, N. D., & Amon, D. (2015). Whale-fall ecosystems: Recent insights into ecology, paleoecology, and evolution. Annual Review of Marine Science. https://doi.org/10.1146/annurev-marine-010213-135144
Bik, E. M. et al. Marine mammals harbor unique microbiotas shaped by and yet distinct from the sea. Nat. Commun. 7, 10516 (2016).

Measurements and calculations for masses of large whale species: How big are the biggest whales?

Whales are often touted as being the biggest living animals on Earth, with the blue whale often cited as the largest animal in Earth’s history. However, not many know how these figures are provided. How do we obtain the size data for such creatures? Is it all malarkey? That is what I’ll be answering today.

Megafauna such as whales, dinosaurs, and many other prehistoric creatures tend to capture the imagination of many by their sheer existence. However, they are often victims of misinformation that even permeated into scientific literature (1). A famous example being the giant squid, which was once commonly stated to have achieved lengths approaching 18 meters in length and weigh as much as a metric ton. It wasn’t until around the past decade did researchers begin verifying the accuracy of recorded specimens and realize that the largest individuals were mainly either unverified claims from the 19th century, specimens that were incomplete, or stretched out beyond their pre-mortem state. Nowadays, it’s generally accepted that the largest giant squids have a total length and mass of ”only” 12 meters and 280 kilograms with the average closer to about 7-9 meters (1). With that in mind, their ”battles” with sperm whales seem more one-sided.

How whale sizes are estimated

But what about the large species of whales? On what basis was it confirmed that the blue whale could surpass 27 meters and 150 metric tons? Well to put it simply, the majority of the existing length and weight estimates the scientific community uses were done using whaling data from the 19th century to the middle of the 20th century. Given the large sample size and how these records tend to span across many decades, they are very useful for comparing temporal and regional size variations of different species and populations. Now length estimates are also corroborated by modern scientific methods on stranded whales and aerial photogrammetry. The total length of a whale is recorded by measuring in a straight line from the snout to the notch within the flukes (1). This length was slightly shorter than the whale’s ”overall” length from the tips of its flukes to the end of the jaw. This convention became standard because the flukes were often cut off by whalers to prevent excess drag as the whale’s carcass was being towed. The jaw was liable to moving around, so the rostrum is used as the anterior endpoint as it could reliably maintain a consistent position.

When measuring from the snout to the fluke, this 1:70 scale blue whale measures 26.6 meters.

Weight estimates are largely based on piecemeal weighing. This method required different sections of the body to be cut up and weighed at a time using pressure cookers or dynamometers. By this technique, we also gained the relative tissue compositions of different whales between their blubber, skeletons, muscles, and internal organs (2). However, this estimation systematically underestimates the entire weight of the intact animal due to body-fluid loss from flensing . Comparative whole-body and piecemeal weighing on smaller specimens revealed a potential error of up to 15% in sperm whales (2). These lost fluids account for about 6% of the body weight in baleen whales and 10% in sperm whales (2). By comparison, blood volume alone accounts for about 7% of total body mass across all mammals (3). So it seems consistent to add these numbers when assessing piecemeal weighing of whales. When averaging the masses for individual lengths, a relationship can be derived between body length and the body weight of a whale. The relationship is expressed through regression formulae. This power function is what’s most commonly used for whales.

Body weight= a(Body length)^b (2)

Here, ”a” and ”b” are constants that are specific to certain species or regional populations of whales. There’s a limitation to these predicted masses, specifically for rorquals, that will be discussed over in the next section. Nonetheless, these formulae are useful as the heaviest specimens ever weighed are often not the largest individuals ever reliably recorded. This is because even piecemeal weighing was a difficult process and at times are most frequently done for smaller individuals.

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Another means for approximating body weight is through oil yields. Masses can be derived from the approximate volume of oil from a whale, converting that volume into blubber weight, and using the ratio of blubber to total weight to calculate the weight of the specimen (4). This data is often useful for estimating historical size trends of depleted populations. While modern methods are useful for evaluating averages, whaling data may still be more valuable for evaluating maximum sizes for these species, as whaling not only depleted populations, but generally targeted the largest individuals, which were often the oldest. Blue whale hunts only ended since the 1970s, reducing the population to less than 1% of its historical size. They currently rest at about 5%. Even with recovery in numbers, younger whales are a much larger demographic than they used to be.

Now with that out of the way, let us evaluate some of the largest whales.

Note: When addressing the average sizes for these individuals, I will be specifically citing the mean sizes at physical maturity. Most casual sources generally report adult size averages that includes sexually mature individuals that are still growing. Generally, it could take an additional one to several decades for a sexually mature whale to stop growing, depending on the species. Hence my earlier point regarding the age distributions of recovering blue whale populations.

The Biggest Whales:

Sperm whale (Physeter macrocephalus): Maximum accepted size- 20.7 meters, estimated 83-88 metric tons.

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I will begin with the sperm whale since this species is the most straightforward. The sperm whale is the largest of the odontocetes, the largest extant animal that is not a mysticete, and among the largest toothed-animals in Earth’s history. Sperm whales are the most sexually dimorphic cetaceans, with physically mature males being over 40% longer and twice as heavy as females. Females enter physical maturity at around 30 years of age and average 11 meters and 14 metric tons; they achieve a maximum size of about 12 meters and 20 tons. By comparison, maturity in males occurs as they approach 50 years old at an average length of 16 meters and 43 metric tons (5). Exceptionally large males can grow to 18 meters or longer. The largest individual to be weighed was an 18.1-meter specimen that was 57.10 metric tons (2). When adjusting for fluid loss, the intact animal was most likely at least 63 metric tons. However, this was only the largest sperm whale to be weighed, records exist for even larger ones.

The largest sperm whale within the whaling record was a 24-meter male caught in the South Pacific in 1933 (1). The credibility for this source is challenged since it was such a large outlier and whaling records have been prone to exaggerating sizes for certain individuals due to quotas or measuring errors. Outside of that report, there are records of eight other bulls ranging from 22.08-22.9 meters in length (1). The largest sperm whale that’s widely-accepted by academics was a 20.7-meter bull caught in 1950 off the Kuril Islands (1). This specimen was officially measured using standard techniques and is recognized by Guinness Records. Credibility for sperm whales of comparable length is further supported by jawbones owned by the Nantucket whaling museum (5.5 meters) , the New Bedford museum (5.2 meters), the Natural History Museum in London (5 meters) and the Oxford University Museum of Natural History (4.7 meters). In large males, the jaws consistently measure to about 25% of their total length. These museum specimens likely belong to individuals ranging from 18.8 (Oxford Museum) to 22 meters (Nantucket Museum). Either way, this provides more physical evidence of male sperm whales achieving lengths of 20 meters. In my personal opinion, I doubt male sperm whales could have historically reached 24 meters in length. I believe 22 meters is a more realistic absolute limit, with the 20.7-meter bull being the largest individual we can be certain of. So how much did it weigh?

A regression formula derived from the piecemeal weights of sperm whales from Antarctica and the North Pacific suggests this relationship.

Mass in metric tons (not adjusted for body fluid)=0.0196(Total Length in meters)^2.74 (2)

Mass in metric tons (adjusted for body fluid)=0.006648(Total Length in meters)^3.18 (5)

There’s an alternative curve, BW=0.00295(TL)^3.55 , that’s based on whole-body weights and estimates larger masses for a given length, but it has a much smaller sample size. When using the adjusted formula, the 20.7-meter bull apparently weighed 101 metric tons. I’m assuming the adjustments designed to account for fluid loss don’t work too well when going outside the length range of the dataset (~18 meters). Luckily, the author does recommend that the non-adjusted formula is still viable by manually accounting for the blood loss. When using the non-adjusted formula and adding the 10% of the body weight back in (divide by 0.90), it comes out closer to 88 metric tons. This more conservative estimate feels more realistic. A more recent formula, that’s based on piecemeal weights from Soviet whaling data, predicts the mass to be about 83.6 tons when adding the body fluids (6).

What allowed sperm whales to grow so large is mainly their foraging behavior. Large body sizes are more energetically-efficient for deep dives while also conferring greater aerobic capacity, increasing their submersion times. The other key factor is that sperm whales are the sole predators for some of their deep-sea prey, so they face very little competition from other animals for resources. The tradeoff is that squid may be a lower quality food source when compared to fish and crustaceans, limiting these creatures from being as large as a few other whale species (1). Compared to females, larger males have more varied diets consisting of larger fish and sharks of up to 3 meters in length.

Blue whales and Fin whales (Balaenoptera musculus and Balaenoptera physalus) Maximum accepted size: 29.9-33.26 meters, 190 metric tons; 26-27 meters, estimated 90-120 metric tons.

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The blue whale is the largest animal ever known to live on Earth. There are multiple subspecies of this creature. The pygmy and North Indian subspecies are the smallest, average 21-22 meters, maxing out at 24.1 meters; the Chilean subspecies averages at 23.5 meters with a maximum for 25.6 meters; Northern Hemisphere blue whales average between 22-24 meters with a maximum of around 27 meters in the North Pacific and 28 meters in the North Atlantic. The largest is the Antarctic subspecies, where mature adults average between 24-26 meters (7,9). Males are slightly smaller than females. The largest blue whale whale scientifically measured was a 29.9-meter Antarctic female, however it is fairly accepted by members of the scientific community that the largest blue whales historically grew beyond 30 meters. This is mainly due to the consistency of whaling data and other sources. Between 1916-1949, 88 blue whales ranging from 30-33 meters have been reported in the Southern Hemisphere (1). The largest ever recorded was a female caught off of South Georgia in 1909 that measured 33.58 meters long (1). Similar to the 24-meter sperm whale, this claim has doubts as it comes from a pre-1920s whaling record, but it is relatively more accepted by authors. The claim of 33.58-meter blue whale, while huge, is relatively less ridiculous than the sperm whale claim. Otherwise, I also see 31 meters commonly listed as the maximum size for blue whales.

Update (4/12/2021) The New Bedford Whaling Museum and Dr. Nick Pyenson of Smithsonian Institution’s National Museum of Natural History support the findings from the 1928 Norwegian study. The measurements themselves where made by whaling directors, but the study describes that they were assigned specific instructions to measure the whales in the official scientific manner, so the scientific measuring technique was still used. They report a female blue whale that was 33.26-meters long and a 32.64-meter long male, both caught off South Shetland in 1926. 5 other whales over 31.38 meters (100 Norwegian feet) were measured between 1922-1925 out of 6,925 whales. Since the New Bedford Museum and Dr. Pyenson approved of these findings, including the fact the study itself describes attention to the scientific standard, I’m inclined to consider this a relatively reliable report. I will add this to the maximum length range above¹⁵

The fin whale is the second longest whale. There are about four subspecies between the North Atlantic, North Pacific, Antarctic, and the pygmy subspecies. The largest of them all are the Antarctic fin whales that average between 21-22 meters when mature and can typically exceed 24 meters. Just as in blue whales, the females are slightly larger than the males. The largest scientifically confirmed individual was a 25.9-meter female, but reports of a 27.3-meter specimen is often cited for many sources. So how much do these two animals weigh?

Well, rorquals are a bit trickier compared to sperm whales because their masses fluctuate wildly depending on the seasons. Migratory whales are primarily seasonal feeders that travel to high latitudes during the summer and feed less for the remainder of the year as they reside in lower latitudes. During the beginning of the feeding season, they are at their lean body mass and they enter their fatten condition by the end of the season. In the Southern hemisphere, blue whales are projected to gain 50% of their lean mass during the feeding season, while fin whales are projected at 30%. However, the fin whale’s weight increase was calculated from a lesser sample size. It’s suspected that the Antarctic fin whale’s seasonal weight gain is closer to a blue whale’s (7). It should be noted that the term ”fat” to described the post-feeding condition for rorquals is misleading. While increases in fat are most certainly observed, most of the weight increases occurs from muscle tissue (7). Female whales lose a lot of weight when lactating for their calves and they can enter a greater fattened condition while pregnant. Due to these effects, the predictive power of formulae are limited, as their data is often a mix of lean, fattened, and intermediate individuals.

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Here, I will specifically be evaluating the Antarctic blue whale subspecies using this formula that’s unadjusted for the 6% body weight loss from flensing.

BW=0.0046(TL)^3.09 (2)

Using their mean body lengths, physically mature male Antarctic blue whales average 102 metric tons and females average 117 metric tons (7). These weights would be roughly intermediate of their two body conditions. The corresponding lean and fatten masses would be 84-125 metric tons for males and 94-140 metric tons for the females (7). The heaviest individual ever weighed was a 27.6-meter female caught on March 20, 1947 (2). One of my sources cites this female as weighing 190 short tons/ 173 metric tons (8); this is the source cited on Wikipedia and has been copied for other websites. However, two of my other sources, in addition to my field guide, suggests it was actually 190 metric tons (1,2,9). I choose to go with 190 metric tons rather than 190 short tons because Wikipedia’s source was a conservation report while my two sources were both specialized studies concerning size metrics. Therefore, it was more likely that a mistake in unit conversion came from the authors of the conservation report. Furthermore, the original paper that cited the specimen was from a 1967 Russian study. The USSR’s use of the metric system by that time made it unlikely that the original figure was written as 190 short tons. The most interesting aspect about speculating the maximum mass is that we know for a fact the largest blue whales were at least more than 2 meters longer than the heaviest weighed individual, so chances are an animal of over 200 metric tons by the end of the feeding season very likely existed within whales 28-30 meters long.

Now for fin whales, the Antarctic subspecies will be evaluated using this formula

BW=0.00989(TL)^2.84 (6)

This formula was specifically applied for ”mid season” weights during January and February, so these whales are relatively more fattened than they were in December. Using this, physically mature Antarctic fin whales of 21-22.2 meters average 60-70 metric tons (6). The heaviest fin whale weighed piecemeal was a 22.7-meter female that weighed 69.54 metric tons, meaning its intact weight was 74 metric tons (2). Using the formula above, the 25.9-meter individual is estimated to have been 108 metric tons and a 27.3-meter specimen could have weighed 125 metric tons. Given how these lengths correspond to the average range for a mature Antarctic blue whale, this sounds about right. These animals share similar tissue compositions, so it makes sense that we’re seeing overlap between weights at equal lengths (2). Granted, this is mainly due to the seasonal variability within both species. At equal lengths, a lean or fattened blue whale will outweigh a fin whale in the same condition. I feel relatively confident about these estimates as my field guide list 120 metric tons as representing a maximum-size individual of 27 meters (9). At the bare minimum, the largest fin whales at least exceeded 90 metric tons according to another formula(2).

What allowed these two species to evolve to such sizes is their very efficient means of lunge-feeding. Despite each dive expending a lot of energy as they experience the drag force of taking in their own weight in water, they very efficiently meet their caloric demands (10,11). While this method grants them far more energy than they expend, it limits them to high-density prey distributions (9).

Gray and Humpback whales (Eschrichtius robustus and Megaptera novaangliae) : Maximum size- 15.6 meters, estimated 45 metric tons; 16 meters, 60 metric tons.

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The gray whale and humpback are both whales well known for their particularly long migrations while also being among the earliest target species for commercial hunts. Mature gray whales average 12.6 and 13.1 meters for males and females respectively (12). They achieve a maximum length of approximately 15.6 meters (9). Humpback whales are of a similar size, with males averaging 13 meters and females at 14 meters (13). They are typically reported reaching an upwards of 16 meters, with at least one account of up to 18.6 meters (9). Being migratory whales, their weight is also observed to fluctuate by the season. The gray whale’s seasonal weight gain is thought to range from 12-41% of the their lean body mass while humpbacks are estimated to approach a doubling of weight (7). A humpback whale is heavier by length than most rorquals, just like the sperm whale (2). Their weight estimates will be using these formulae:

Gray whale BW=0.0051(TL)^3.28 (2)

Humpback BW=0.0158(TL)^2.95 (2)

The mass of the average adult gray whale is 22-25 metric tons with the maximum being 44 metric tons. By comparison, the heaviest specimen weighed piecemeal was a 13.6 meter-female that was approximately 36 metric tons after adjusting (2). For the humpback, the average individuals ranged from 32-40 metric tons. A 16-meter humpback would have been approximately 60 metric tons and a 18.6-meter specimen would weigh 93 metric tons. The largest piecemeal weight was 43 metric tons for a 13.8-meter female (2). I would avoid citing the 18.6-meter individual as there’s relatively little substantiating humpbacks reaching such sizes. The 16-meter estimate seems much more realistic.

Overall, these results are very consistent to what I’ve seen reported by most sources, including my field guide (9). Gray whales primarily suck and filter food from the bottom of sea beds and may occasionally partake in skim or gulp-feeding. Humpbacks employ a larger diversity of feeding techniques ranging from lung-feeding and use of bubble nets to trap small fish (9).

North Pacific Right Whales and Bowhead whales (Eubalaena japonica and Balaena mysticetus): Maximum size- ~20 meters for both species; 114 metric tons and 120-164 metric tons.

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On a mass per length basis, these two species surpass all others. Right whales and the bowhead whale are the stockiest whales ever known. Both are members of the Balaenidae family, with the North Pacific right whale being the largest of the three species within its genus. Both inhabit cold high-latitude waters in the Northern hemisphere, though bowheads are true arctic residents who don’t migrate southward. Bowhead whales and North Pacific Right whales are basically the same size with most mature adults ranging from 15-17 meters in length and 60-80 metric tons in weight (9). As for their maximum lengths, right whales as large as 19.8 meters have been reported, with some sightings of individuals surpassing 20 meters (14). The longest measured bowhead whales approach 18 meters, but reports of some whales beyond 20 meters are also reported from 19th-century sightings and contemporary accounts by Inuit hunters (4). There’s little rejection among experts that bowheads could exceed 20 meters due to their similarity to the right whale and the lack of a robust dataset to compare against, like we do for sperm whales or blue whales. Whaling records for bowhead whales are predominantly oil yields.

Despite formulae existing for both species, I’m not going to go in-depth with the relationship for evaluating the body length-mass relationship. I have emphasized it for the other species because those cases had more extensive data regarding their average and maximum lengths. Here, the details on the longest confirmed individuals are more ambiguous, especially in the case of the bowhead whale. I will instead focus on direct measurements for the North Pacific right whale and sizes derived from oil yields for the bowhead. I will say, however, that the size curves for both species’ regression formulae were quite similar (2,4).

The largest North Pacific Right whale ever weighed was a 107 metric ton individual of 17.4 meters, that would have weighed 114 metric tons when adjusted. (2). This is the first time we have a direct measurement telling us of a non-blue whale weighing over 100 metric tons. Chances are that longer right whales would typically weigh around this mass or greater.

In order to infer the masses of historically caught bowhead whales, we need to convert the individual’s oil yield to calculated their blubber weight. Oil volumes from bowhead whales were measured in barrels (31.5 US gallons), and 193.4 kilograms of blubber was necessary to yield a barrel(4). The blubber composes about 44% of a bowhead whale’s mass, essentially the same as in the North Pacific right whale (4,2). Therefore, about 228 barrels of oil would be the expected amount from a bowhead whale that weighed 100 metric tons. Records of bowheads providing 250 or more barrels are well documented (4). There’s even one case of an individual providing 375 barrels, that would equate to a 164-metric ton animal (4)! Assuming that particular volume was accurately measured, this record provides physical evidence supporting the existence of the 20+ meter individuals reported by both explorers and Inuit witnesses. Given the general reliability of the oil yield records in addition to the North Pacific right whale serving as a strong proxy for making morphometric inferences, there’s very little room to doubt the largest bowheads surpassed 100 metric tons.

These two species evolved to such astonishing sizes because they spend much of their time in cold and rich waters where they skim-feed at the surface into huge clouds of prey using their large mouths(9). The relatively lower cost compared to lunge-feeding provided balaenids with an advantage in achieving their sizes.

Concluding thoughts

You may have noticed how I brought attention to the role of the whales’ feeding strategies in acquiring their large sizes. I have done this to address a misconception that had caused some to become unenthusiastic of a whale’s size: the water was what enabled them to grow so large. What people tend to overlook is that while buoyancy may provide an advantage in supporting their weight, there are other factors involved in limiting the evolution of gigantism. The crucial disadvantage of marine environments is the lack of an efficient dietary niche that is as viable as the terrestrial herbivore’s.

The largest terrestrial animals such as sauropods that approached 80 metric tons and large Cenozoic mammals potentially achieving 20 metric tons were all strict herbivores. Plants were both abundant and imposed little cost to consume, making them the ideal food source for meeting the energy requirements for large creatures, say 15 tons or greater. Plant biomass in the ocean is very low, requiring most animals to be a predator of some sort. This is evident as cetaceans evolved from plant-eating artiodactyls to becoming carnivores as they adapted to aquatic life.

A carnivorous niche appears to heavily neutralize the advantages that buoyancy provides in attaining large sizes when compared to terrestrial herbivores. This is evident by the lack of marine taxa outside of whales that can be confidently interpreted as surpassing the largest sauropods in mass. Even the largest non-whale filter-feeders such as the Leedsichthys and whale sharks are not conservatively expected to reach 60 tons. Even baleen whales, who have been fully aquatic for 40 million years and had baleen for 25 million, averaged between 5-8 meters, with the largest species being 13 meters during most of the Miocene. Widespread gigantism did not evolve in the ancestors of modern whales until about 4 million years ago, coinciding with ecological shifts of the ocean. Macropredators such as Megalodon and Livyatan were only so large because of the unusual circumstances that was maintained by a fragile ecological balance. Once small baleen whales became extinct and replaced by larger, migratory whales, the macropredators died off. This is all evident of how the energy requirements, in addition to the eventual diminishing of a creature’s speed and agility, makes large bodies very unfit for marine animals that need to hunt their prey.

With all of this in consideration, the idea that the largest animals known to exist were actually marine carnivores rather than a terrestrial herbivore should undermine expectations. Whales’ large sizes coincided with their ecological roles, and that will be the topic for my next article.

I hope everyone reading found this article interesting and informative. If anyone has any objections towards my methodology or assessment of the data present by my sources, please get in touch so we can discuss it. And apologies for interchangeably using ”weight” and ”mass” throughout the article. I know these are different terms, but in this context they serve the same practical meaning. I learned a lot while preparing for this article, so I’m eager to learn more.

Works Cited

1.McClain, C. R., Balk, M. A., Benfield, M. C., Branch, T. A., Chen, C., Cosgrove, J., Dove, A. D., Gaskins, L. C., Helm, R. R., Hochberg, F. G., Lee, F. B., Marshall, A., McMurray, S. E., Schanche, C., Stone, S. N., & Thaler, A. D. (2015). Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ, 3, e715. https://doi.org/10.7717/peerj.715

2.Lockyer, Christina. (1976). Body weight of some species of large whales. Ices Journal of Marine Science – ICES J MAR SCI. 36. 259-273. 10.1093/icesjms/36.3.259

3.Lindstedt, Stan & Schaeffer, P. (2002). Use of allometry in predicting anatomical and physiological parameters of mammals. Laboratory animals. 36. 1-19. 10.1258/0023677021911731.

4. George JC, Bockstoce JR, Punt AE, Botkin DB (2007) Preliminary estimates of bowhead whale body mass and length from Yankee commercial oil yield records. Cent Study Environ 98105:5020

5. Lockyer C. 1981. Estimates of growth and energy budget for the sperm whale, Physeter catodon. Mammals in the Sea. vol. 3, FAO Fisheries Series, pp. 489–504.

6.Mikhalev, Yuri. (2019). Whales of the Southern Ocean: Biology, Whaling and Perspectives of Population Recovery. 10.1007/978-3-030-29252-2.

7.Lockyer, Christina & FAO, Rome & FI, & Mammals, Advisory & (Norway, Bergen & Aug,. (1981). Growth and energy budgets of large baleen whales from the southern hemisphere. XF2006134403 FAO Fisheries Series. 5. 379-487.

8.COSEWIC 2002. COSEWIC assessment and update status report on the Blue Whale Balaenoptera musculus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 32 pp.

9.Carwardine, M. (202o). The Handbook of Whales, Dolphins and Porpoises of the World. Princeton, New Jersey: Princeton University Press.

10.Goldbogen, Jeremy & Pyenson, Nicholas & Shadwick, Robert. (2007). Big Gulps require high drag for fin whale lunge feeding. Marine Ecology-progress Series – MAR ECOL-PROGR SER. 349. 289-301. 10.3354/meps07066.

11.Fossette, S., Abrahms, B., Hazen, E. L., Bograd, S. J., Zilliacus, K. M., Calambokidis, J., Burrows, J. A., Goldbogen, J. A., Harvey, J. T., Marinovic, B., Tershy, B., & Croll, D. A. (2017). Resource partitioning facilitates coexistence in sympatric cetaceans in the California Current. Ecology and evolution, 7(21), 9085–9097. https://doi.org/10.1002/ece3.3409

12. Selina Agbayani, Sarah M E Fortune, Andrew W Trites, Growth and development of North Pacific gray whales (Eschrichtius robustus), Journal of Mammalogy, Volume 101, Issue 3, 22 May 2020, Pages 742–754, https://doi.org/10.1093/jmammal/gyaa028

13. Baird, R.W. 2003. Update COSEWIC status report on the humpback whale Megaptera novaeangliae in Canada in COSEWIC assessment and update status report on the humpback whale Megaptera novaeangliae in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 1-25 pp.

14. Ivashchenko YV, Clapham PJ (2011). “Pushed to the Edge: Soviet Catches of Right Whales in the Eastern North Pacific”. Alaska Fisheries Science Center Quarterly Research Reports (Apr–May–June

15. Risting, S. (1928) Whales and whale foetuses: statistics of catch and measurements collected from the Norwegian Whalers’ Association 1922–1925. Rapports et Procès-Verbaux Des Réunions, 50, 1–122.

The Horned and the White Whales

Life History and Growth

Table 1 : Size parameters for D. leucas

Table 2: Size parameters for M. monoceros

Body weight

Figure 1: Weight data for D. leucas

Figure 2: Weight data for M. monoceros

Validating Govorkov’s data

Figure 3: Reported measuring scheme from Govorkov, 1934

Figure 4: Fluke width comparisons between Okhotsk Sea with Far East Belugas

Table 3: Fluke width and estimated TL from Govorkov, 1934

Table 4: Real and estimated masses from Govorkov, 1934

Weight relationships.

Table 5: Power function parameters for Monodontidae

Figure 5: Comparison between mass data for M. monoceros and D. leucas.

Maximum possible weight

Figure 6: Comparison of weight data for St. Lawrence belugas

What’s next?

References

The diminutive sperm whales

Table 1: Size parameters for Kogia species from South Africa and Australia (Plön, 2004)

Building the database

Figure 1: Data extraction for Platanista

Figure 2: Weight data for Kogia

Figure 3: Fields for data entries

Figure 4: Weight relationships for some odontocetes

Figure 5: Example of entries found in multiple sources.

Current Progress

References

Introduction

Table 1: Size parameters for different species of River dolphins

Mass data

Figure 1: Mass data for River dolphin species.

Table 2: Mass-length formulae parameters for river dolphins

Table 3: Mass estimates for Pebanista

Concluding thoughts

References

Flaws in the traditional approach?

Table 1

Figure 1

Comparing fitting methods

Table 2

Figure 2

Table 3

Connecting weight to growth

Figure 3

Parting news

References

Life History and Growth

Figure 1

1(7/22/2023 Update: I’ve recently found that the raw age data that was analyzed in Clarke et al., 1994 was available in the appendix of the previous part of their studies of Southeast Pacific sperm whales. I have since updated figures 3&4 and the accompanying parameters to reflect this change)

Figure 2

Figure 3

Figure 4

Figure 5

Taxonomic history and anatomical differences between regions: multiple subspecies?

Figure 6

Maximum size

References

The size-rivals

The Overlooked Rorqual

The Corpulent Balaenids

Final Ranking?

Triassic Giants!

The Final Ranking

Acknowledgements

Sources

Introducing the ”Whale Killer”

To Kill a Leviathan

An unexpected challenger

Remaining Mysteries

Sources

Introduction: Nomenclature and taxonomy

How blue whales were measured

How Big Is The Average Blue Whale?

Table 1

Table 2

What was the Biggest Blue Whale?

The Heaviest Blue whale to be weighed

Estimated Tabulation of Slava’s 190-tonne Whale

¹(7/22/2023 Update: I’ve recently found that the raw age data that was analyzed in Clarke et al., 1994 was available in the appendix of the previous part of their studies of Southeast Pacific sperm whales. I have since updated figures 3&4 and the accompanying parameters to reflect this change)