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 / 330.5a | 260.4 / 274.3b |
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 20th 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.
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
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
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
Lockyer, C. (1993). Seasonal Changes in Body Fat Condition of Northeast Atlantic Pilo Whales, and their Biological Signficance. Report of the International Whaling Commission (Special Issue), 14, 325–350.
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.
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