A new study led by the University of British Columbia (UBC) has found that the already endangered southern resident killer whale populations are significantly undernourished since 2018. These animals have been in an energy deficit (meaning the energy they got from food was less than they expended) for six of the last 40 years, with three of those six years occurring from 2018 to 2020. During this period, they consumed on average 17 percent less than what is needed to reach the required energy levels for an adult killer whale.
“With the southern resident population at such a low level, there’s a sense of urgency to this kind of research,” said study lead author Fanny Couture, a doctoral student at the Institute for the Oceans and Fisheries (IOF) at UBC. “Both killer whales and Chinook salmon, the southern resident’s main prey, are important, iconic species for the west coast of Canada. Studying what is happening to the population may help offer solutions, both for the southern residents and potentially other killer whale populations in the future.”
As of October 2021, the southern resident whale population numbered 73 individuals – a much smaller number than that of the increasing northern resident population of about 300. According to the experts, the growth of the southern resident population is most likely impeded by lack of food, due to significant declines in Chinook salmon.
The decrease in Chinook salmon abundance could be attributed to many factors, including climate change, predation by other animals, and greater susceptibility to disease. The researchers found that, during years when Chinook populations were at low levels, southern residents would consume more chum salmon, showing that the animals can switch to other salmon species when the abundance of their primary prey declines.
However, in the 1990s – following observations of declining Chinook populations – commercial fisheries for this species of salmon in Canada were reduced. However, this did not seem to solve the problem. “Those declines have continued despite severe fisheries reductions, and one very likely candidate for causing them is the massive increase in abundance of Steller sea lions since the mid-1980s; those sea lions now consume more fish than all the British Columbia commercial fisheries for all species, combined,” explained study senior author Carl Waters, a professor emeritus at IOF.
Nonetheless, the scientists argued that the dire situation in which the southern resident killer whales currently find themselves calls for a reduction in the catch of larger Chinook salmon, by promoting fishing techniques that increase the chance of survival of larger fish. Moreover, since underwater noise pollution from boats may also affect southern residents’ foraging habits, urgent measures should be taken to reduce noise pollution in order to safeguard this threatened species.
The study is published in the journal PLoS ONE.