Southern resident killer whales do not lack summer prey: UBC researchers

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Researchers at the University of British Columbia say they have “exploded” a common belief that southern resident killer whales lack summer prey in Canadian waters.

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Endangered orcas feed on Chinook salmon, their feeding grounds scarce during the long summer compared to their more populous cousins, the northern resident killer whales.

Scientists now say that Chinook salmon numbers are four to six times more abundant in the Salish Sea during the summer for southern residents than for northern resident feeding grounds.

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“People are talking about the lack of prey as if it’s a fact, but this is the first study to measure and compare the amount of their preferred prey, Chinook salmon, available to southern and northern resident killer whales,” said Chief said author Mei Sato, a research associate at the UBC Institute for the Oceans and Fisheries at the time of the study, in a UBC news release.

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NS report published on Tuesday The Canadian Journal of Fisheries and Aquatic Sciences compared Chinook availability for southern residents in the Juan de Fuca Strait with availability for northern residents in the Johnstone Strait between 2018 and 2019.

Using sonar, the researchers found that the size and distribution of fish were similar in both areas, but that many more fish from Juan de Fuca were “study areas”.

As it stands, scientists believe there are about 73 southern resident killer whales left in the world, and a growing population of about 300 northern inhabitants, which are threatened but not endangered.

The slender stature of southern residents may have contributed to the belief that they have less summer prey, Sato said, but new research suggests that the food shortage “might not be” when feeding in the Salish Sea in the summer. has been”.

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The research did not evaluate other factors that might prevent southern residents from actually catching their prey, such as increased vessel traffic and noise in their traditional feeding grounds.

Both Sato and study co-author Andrew Trites, director of the UBC Marine Mammal Research Unit, say research efforts should now focus on other climates and factors that affect Chinook availability.

“To answer the question of whether there is a total hunting deficit, we still need to figure out what is happening during winter and spring,” Sato said, adding that there are significant year-to-year fluctuations. and in different places these whales travel. , like California.”

The research was funded by Fisheries and Oceans Canada, and was conducted with the help of sport and commercial fishermen, the Sport Fishing Institute of BC, and several whale watching companies.

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