Researchers at the University of British Columbia say noise may be a critical factor that keeps endangered killer whales in Puget Sound from getting enough of plentiful Chinook salmon.
While looking into the demise of a specific group of southern resident killer whales, researchers didn’t find what they expected, said Andrew Trites — director of the marine mammal research unit at UBC and co-author of the report, which was first published by The Canadian Press.
The researchers had spent months tracking the two whale populations’ preferred food in the Salish Sea and the waters of northern Vancouver Island. At length they pinpointed the noise factor.
Vessel noise can “mar communication between pod members and interfere with foraging and navigation — and the physical presence of vessels can also reduce foraging efforts,” the study said.
“When you find what you don’t expect, then you look even harder at your data, and your first thought is you must have done something wrong,” said Trites, in comments published by the Canadian Press on Oct. 14.
The latest census of the endangered southern resident orcas reported 73 whales, compared with the growing population of northern resident orcas, who number about 200. The report found Chinook salmon to be twice as prevalent in the southern residents’ feeding areas compared to those of northern residents.
“This implies that southern resident killer whales have greater access to chinook salmon compared to northern residents during summer — and that any food shortage southern residents may be encountering is occurring at other times of year, or elsewhere in their range,” said the study.
Researchers had collaborated with commercial and sport harvesters and whale-watching firms to identify feeding areas from the entrance of Juan de Fuca Strait off southern Vancouver Island and the mouth of the Frazer River, up to waters off the northern end of Vancouver Island. The gap between these two groups of fish-eating whales has been attributed to ecological and biological differences between regions, including salmon availability, competition, physical disturbance, underwater noise, contaminants, and inbreeding.
The study said that food availability likely plays the greatest role in limiting their carrying capacities.
Noise is more common in southern waters and prevents southern residents from catching prey, Trites said.
“It’s a bit like going into a busy supermarket and you are shopping with somebody else, but you can’t tell each other what to get because it’s too noisy,” he said.
The study notes that killer whales are more likely to encounter greater numbers of vessels in the Salish Sea than in the north (Vancouver Island) waters, and that could mean salmon are less accessible to southern resident orcas than to northern resident orcas, despite there being a higher abundance of Chinook, according to the study.
“While we really want to save southern resident killer whales, we need to think bigger and not assume that we’ve solved the problem, because if we’re wrong, we’re dooming them to extinction,” Trites said.
