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 | Lb (cm) | Lsm (cm) M/F | L∞(cm) M/F | Lmax M/F | Source |
| W. Hudson Bay | 151 | 310 / 290 | 377 / 328 | 448 / 400 | (Doan & Douglas, 1953; Doidge, 1990b; Sergeant, 1973) |
| E. Hudson Bay | 316 / 280a | 349 / 330 | 440b / 400b | (Doidge, 1990b, 1990a) | |
| Cumberland Sound | 160 | 378c / 308 | 427 / 362 | 450b / 400b | (Brodie, 1971; Luque & Ferguson, 2010) |
| White & Kara Seas | 160 | 380d / 350 | 438 / 378 | 479 / 420 | (Heide-Jørgensen & Teilmann, 1994; Kleinenberg et al., 1969; Ognetov, 2007) |
| Alaska | 155 | 369e / 289 | 432f / 370f | 485 / 410 | (Burns & Seaman, 1986; Suydam, 2009) |
| St. Lawrence Estuary | 160 | 381g / 336g | 416 / 365 | 456 / 409 | (Lair et al., 2015; Lesage et al., 2014; Vladykov, 1944) |
| W. Greenland | 155a | 390 / 345 | 483 / 386 | 545 / 482 | (Degerbøl & Nielsen, 1930; Heide-Jørgensen & Teilmann, 1994) |
| Okhotsk Sea | 170 | 390h / 343i | —j / 390 | 590a / 490a | (Dorofeev & Klumov, 1936; Kleinenberg et al., 1969) |
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 | Lb (cm) | Lsm (cm) M/F | L∞ (cm) M/F | Lmax 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. Greenlanda | 463 / 406 | 501 / 441 | (Garde et al., 2022) |
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 20th 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 | 401a | 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 |
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 | 215a | 119.5678005 |
| M | 667 | 367 | 1412 | 3946.653259 |
| M | 576 | 270 | 1956b | 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 | 448a,c | 197.0318359 |
| M | 190 | 116 | 202a | 110.0530961 |
| M | 170 | 113 | 194a | 84.80956762 |
| M | 153 | 94 | 160a | 58.84386526 |
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. leucasa | 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 | 9b | Robeck et al., 2005 |
| D. leucas | Male | Captive | 40.84 | 2.132 | 5b | Robeck et al., 2005 | |
| D. leucas | Female | Captive | 47.50 | 2 | 4b | 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 |
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
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Arsenʹev, V. A. (1939). Distribution and Migration of the Far Eastern Beluga. Izvestiya TNIRO, 15.
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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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