Beaked whales are estimated to make up more than 25% of cetaceans, however, the toothed whales are elusive and therefore incredibly difficult to study. Some species of beaked whales have never been observed alive and are only known from stranded carcasses. Some carcasses have been found in Europe, some in North America, but their exact spatial range is unknown. The low number of observations in the wild leaves researchers at a loss not only on the whales’ biology, but more importantly, on how to protect the species we know next to nothing about.
A new study by Kerri Smith and colleagues now shines some light on the mystery that is beaked whales and proposes a new study method to understand such cases better. Through their diet, stable isotopes get incorporated in the animal’s tissue at different rates, depending on the tissue’s growth and replacement rate. By comparing the isotope composition, questions about the species diet and spatial range can be answered.
In this study, carbon and nitrogen isotope composition in different tissues was compared in 102 Sowerby’s beaked whale samples from the east and west Atlantic. Since beaked whale carcasses are found only seldomly, the researchers had to rely on “specimen of opportunity”, ie. random samples mostly from bycatch or museum exhibits, with little control over how the samples had been collected. Still, even those “small pieces of a large, complex puzzle” can tell a lot about distribution, behaviour and the whales’ life.
The results showed that there are at least two distinct populations of Sowerby’s beaked whales: one in the eastern and one in the western Atlantic. Researchers suggest further explorations into genetic differentiation between the populations. The study also shows that specimen of opportunity can be a valuable source of information and a treasure trove of data just waiting to be explored.
Based on the findings, Smith concludes that “a key action to take going forward is generating more fundamental data through studies like this one - successful conservation action requires a strong foundation of reliable data, and there is still so much we do not know about beaked whales and many other marine species. As we learn more about them and their habitats, we may need to set aside important habitats as marine protected areas. Additional research to identify the potential influence of fishing activities and naval sonar on critical beaked whale habitats is also needed."
The full study can be found here: Smith, K. J., Trueman, C. N., France, C. A., Sparks, J. P., Brownlow, A. C., Dähne, M., ... & Peterson, M. J. (2021). Stable isotope analysis of specimens of opportunity reveals ocean-scale site fidelity in an elusive whale species. Frontiers in Conservation Science, 2, 13.