A leading assumption about the dwindling numbers of southern resident killer whales blames a lack of salmon, but a study from the University of British Columbia found that they have double the number of chinook available in the summer than their much larger cousins. healthy, those from the north. residents.
Researchers spent months tracking the preferred food of two whale populations in the Salish Sea and northern waters off Vancouver Island and their findings have now been published in the peer-reviewed research journal PLOS One.
Andrew Trites, co-author of the report and director of the university's marine mammal research unit, said they didn't find what they expected.
“It was surprising,” Trites said of his first reaction to the discovery.
“When you find what you didn't expect, you analyze your data further and your first thought is: you must have done something wrong.”
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This month's latest census of endangered southern residents revealed they number just 73, compared to the growing population of northern residents of around 300.
Trites said he double- and triple-checked the numbers of salmon found during the summer of 2020.
“I think I've learned over time that we need to be careful about jumping to conclusions,” he said.
The report found that chinook were twice as prevalent in the feeding areas of southern residents compared to those of northern residents.
“This implies that southern resident killer whales have greater access to chinook salmon compared to northern residents during the summer – and that any food shortages that southern residents may be experiencing are occurring at other times of the year, or elsewhere in its range,” the published study said. October 10th.
Trites said researchers collaborated with commercial and sport fishermen and whale-watching companies to identify feeding areas from the entrance to Juan de Fuca Strait on southern Vancouver Island and the mouth of the Fraser River to the waters at the far end. northern Vancouver Island.
The growing population gap between the two groups of fishing whales has been variously attributed to ecological and biological differences between regions, such as salmon availability, competition, physical disturbance, underwater noise, contaminants, and inbreeding.
“However, food availability likely plays the most important role in limiting their carrying capacity,” the study of southern residents said.
Trites said noise is more common in southern waters, which deters southern residents from catching prey.
“It's like going into a busy supermarket and shopping with someone else, but you can't tell each other what to buy because it's too noisy.
“It’s so busy with so many people that you can’t hear each other, you can’t talk about what you’re trying to make for dinner,” Trites said.
The study states that noise from vessels can “mask communication” between group members and interfere with foraging and navigation – while the physical presence of vessels can also reduce foraging efforts.
“Killer whales are more likely to encounter a greater number of ships in the Salish Sea than in North Island (Vancouver) waters, which may mean that salmon are less accessible to southern residents than northern residents, despite of there being a greater abundance of chinook,” the study said.
Trites said some may find the study's results difficult to accept, but it could make people rethink their assumptions.
“And I think if we really want to save the southern resident killer whales, we need to think big and not assume we've solved the problem, because if we're wrong, we're dooming them to extinction,” Trites said.
