Cetaceans found themselves in an energy deficit for six of the forty years studied.
Crucially, of those six years of deficit, three were from 2018 to 2020. The average energy difference amounted to more than 28,000 calories, or about 17% of the daily energy required for an average adult killer whale. , according to the authors. Other deficit years were 1983, 2008 and 2012.
The energy needs of large warm-blooded marine mammals are particularly high due to the requirements for regulating their body temperature and foraging, the study said.
Fanny Couture, a marine ecologist at the University of British Columbia’s Institute of Fisheries and Oceans, and co-author of the study, explains that all of this is worrisome because Southern residents are a very small population
.
While the northern resident killer whales have a population of around 300 individuals, the southern ones are more threatened and have only 73 individuals. Since 2008, the species has been listed as endangered in the United States and Canada.
Threats to Southern Resident Killer Whales include shipping traffic and associated underwater noise, toxic contaminants, and dwindling food resources.
” [Il faudra faire de futures recherches] to understand how this energy deficit, therefore the fact that [épaulards] do not eat enough, influences [sur] their behavior, but also influences [sur] the demographic trajectories of this population, that is to say births as well as deaths. »
Chinook salmon make up 90% of their diet
Southern Resident Killer Whales spend about 80% of their time in the Salish Sea during the summer months, and travel extensively through Juan de Fuca Strait, Haro Strait and the southern part of the San Juan Islands.
In recent years, sightings of these cetaceans in British Columbia have been closely linked to salmon runs from May to October on the southern tip of Vancouver Island.
Chinook salmon make up 90% of the diet of Southern Resident Killer Whales during the summer months. But most wild populations of this northeast Pacific fish have recently experienced declines.
” There are more and more images, especially using drones, which show that [épaulards] become increasingly lean and lose their fat stores. »
The study was unable to collect data in winter, as the whereabouts of Southern Resident Killer Whales are unknown during this season. Fanny Couture specifies that there is more and more [d’indices] which show that the [épaulards] southern residents would be able to diversify a bit what they eat during the winter
.
In late September and October, SRKWs tend to feed on coho and chum salmon as well, indicating that they are adapting as their favorite food becomes scarce.
Comparing figures between 1979 and 2020, the researchers found that overall fish abundance had declined by around 20-40%.
Seasonal consumption of chinook salmon by killer whales from April to October would have ranged from approximately 216,000 to 166,000 fish between 1979 and 2020. The highest consumption would have been in 1993, and the lowest in 2018.
Salmon prized by sea lions
In a press release, the lead author of this study, Dr. Carl Walters, explains that the commercial fishery for chinook salmon in Canada was reduced in the late 1990s following observations of a decline in abundance. .
[Mais] these declines have continued despite severe reductions in fishing
, he wrote. He says the massive increase in Steller sea lion abundance since the mid-1980s could explain the decline in Chinook salmon.
In addition to the predation of other species, other factors could explain their decline, such as fishing, warming water and perhaps an increase in diseases linked to climate change, lists Fanny Couture.
As for northern resident killer whales, researchers don’t know if they too are energy-deficient, so that could be the subject of future research, the ecologist says.
The researchers conclude that future conservation and fisheries management decisions must focus on the recovery of individual Pacific salmon.
Reference-ici.radio-canada.ca