(ORDO NEWS) — Studying the diets of wild animals is often difficult, but now there is a new method: by analyzing the composition of the subcutaneous fat of bowhead killer whales, an international team of scientists was able to quite accurately assess what these whales mainly feed on.
Killer whales ( Orcinus orca ) are intelligent and highly adaptable marine predators, able to satisfy their food needs with both small fish and giant whales. As the ice in the Arctic Ocean melts, killer whales have begun to invade the polar waters and spend more and more time there, posing a potential threat to local animal species.
The study of animal diet composition is vital to assessing the dynamics of ecosystem food webs, especially in the case of top predators such as cetaceans, which can regulate entire food webs through food cascades.
Unfortunately, little is known about the diet of cetaceans (especially its interpopulation and intrapopulation differences) , and to the greatest extent this concerns animals from remote regions of the World Ocean.
To assess the trophic interactions of killer whales living off the coast of Greenland, the scientists decided to conduct a quantitative fatty acid analysis (QFASA) of subcutaneous adipose tissue, which allows the composition of lipids to track the food sources of large predators.
This method has been repeatedly used to study animals in captivity in the past, but not in free-living cetaceans, because their subcutaneous fat samples rarely fall into the hands of scientists.
After studying the fat samples of 12 killer whales and about half a thousand of their potential victims (fish, seals and other whales), scientists found that the diet of these predators consisted mainly of seals, such as harp and hooded seals, and fish, mainly Atlantic mackerel.
These data are consistent with the results of the analysis of the contents of the stomachs of killer whales, which allows us to talk about the prospects for using the QFASA method for further studies of the diet of whales.
Summing up, we can say that while killer whales living off the coast of Greenland mainly feed on numerous species of fish and seals, while the share of whales in their diet does not exceed 20%.
However, the data obtained cannot be extended to other killer whale populations, which can seriously differ in their preferred prey: for example, it is known that off the coast of Canada they often hunt narwhals and bowhead whales, while those living off the coast of Denmark, on the contrary, lean more on herring and mackerel.
To fully appreciate the impact of killer whales on polar ecosystems and the possible consequences of their longer stay in northern waters, a larger study of subcutaneous fat samples of these animals from different populations will be required.
The QFASA method can allow analysis of even small fragments of carcasses, which will undoubtedly make life easier for marine biologists and allow us to deepen our understanding of the ecology of killer whales and other cetaceans.
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