Permanent southern killer whales have suffered from an “energy deficit” from lack of food for six of the last 40 years. | DFO
Resident killer whales (SRKW) have suffered an “energy shortage” of food shortages in local waters in recent years, according to a new study that recommends the use of size-selective fishing methods and practices to protect the oldest and most -large salmon.
The SRKW population has shrunk to about 73 in recent years, while their northern cousins are at a stable 300.
The presence of chinook salmon, which is their main diet, is thought to be the main reason for the relative decline in the SRKW population.
Researchers at the University of British Columbia recently estimated chinook populations in the Salish Sea of British Columbia, where SRKW feed during the summer months.
They conclude that SRKW has been in an “energy deficit” for six of the last 40 years. Energy deficiency means that they consume fewer calories than they burn.
“Three of these six years come in the last years of the study – 2018 to 2020,” the study said.
SRKW spends only a few months each year at BCwaters, so food shortages may not be a strictly local phenomenon. They may find it difficult to find enough food in other parts of the Pacific, such as California.
“It’s very difficult for us to know exactly where they happen, and the field work is really hard in the winter, so we definitely lack some data there,” said Fanny Couture, a doctoral student at the Institute of Oceans and lead author of fisheries and research. BIV News.
Chinook, derived from the Fraser River, the Columbia River and the Budget Sound, accounts for about 82% of SRKW’s diet, although koho and keta also make up a significant amount of their diets in September and October.
“In fact, koho and ketti may make up between 20% and 50% of SRKW’s diet during this period,” the study estimates.
Killer whales not only prefer chinook – they prefer the largest and oldest chinook, and it is the reduction of these large older fish (four and five years old) that seems to be largely responsible for the whales’ periodic energy deficits.
The study confirms what some coastal first nations have been saying for years: the exploding population of seals and sea lions is at least partly responsible for reducing the availability of salmon, especially chinook. The study estimates that harbor seals eat more chinook than SRKW.
“In 2020, our model predicts that SRKW will consume about 800 adult chinook salmon per day, compared to 1,000 for port seals,” the study estimates.
In a press release from UBC, Carl Walters, an honorary scientist at the Pacific Biological Station and a research associate, noted that pinnipeds also eat more chinook than commercial fishermen.
Chinook commercial catches declined in the late 1990s in response to declining chinook numbers, he said.
“These declines continue despite a serious decline in fishing, and one very likely candidate for causing them is the huge increase in the abundance of Steller sea lions since the mid-1980s,” Walters wrote. “These sea lions now consume more fish than all commercial fishing activities in BC for all species combined.
Steller’s main diet for sea lions is herring, but Couture said there is growing evidence that they also eat more salmon.
“It really varies by season, and there’s more and more evidence that they feed on more and more salmon, including chinook,” Couture said. “And there’s also growing evidence that they feed on relatively large chinook salmon.”
Despite the reduction in the allowable catch for commercial chinook fishing, it is believed that fishermen still catch more chinook each year than killer whales eat.
“Although chinook salmon fishing in marine waters has been drastically reduced since the 2000s, the average annual number of adult chinook salmon caught by fisheries between 2010 and 2020 is 198,530, while around 187,200 fish are caught. were consumed annually during this period of the study, the SRKW assessment.
“In this way, the predictions of our model reinforce the importance of applying size-specific selectivity to chinook salmon fishing on the Northeast Pacific coast, as well as the use of fishing techniques that promote the survival of larger individuals.
The authors of the study do not specify whether size-selective methods should be introduced for the commercial or sport fishing sector, or both.
The study also calls for pinniped predation to be taken into account “when meeting future conservation objectives”.
nbennett@biv.com
@nbennett_biv
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