Recent Research Has Uncovered New Details About The Diet Of Resident Killer Whales, Aiding Conservation Efforts For Critically Endangered Populations
A team of researchers from the University of Washington and the National Oceanic Atmospheric Administration has uncovered more information about what resident killer whales or orcas are eating. It has long been known that they like to hunt fish, particularly salmon.
However, some populations of resident killer whales are thriving, and others are struggling to survive. So, the researchers want to learn more about the role that diet plays in their survival.
“Killer whales are incredibly intelligent and learn foraging strategies from their matriarchs, who know where to find the richest prey resources in their regions,” said Amy Van Cise, an assistant professor of aquatic and fishery sciences at the University of Washington. ”
‘So we wanted to know: Does all of that social learning affect diet preferences in different populations of resident killer whales or in pods within populations?”
The team studied the cuisine preferences of two resident killer whale populations—the Alaska residents and the southern residents, which live in the Salish Sea and off the coasts of Washington, Oregon, and northern California.
Both populations had a tendency to favor salmon, especially Chinook, chum, and coho. But they showed differences when it came to hunting.
They ate different salmon species at certain times of the year and pursued other fish species to supplement their diets.
The study will aid conservation efforts for southern resident killer whales from northern California to the Gulf of Alaska. They are critically endangered, while other populations are increasing in size.
“We know that lack of food is one of the main threats facing the endangered southern resident killer whales,” Van Cise said.
Thomas – stock.adobe.com – illustrative purposes only, not the actual whale
“We figured that if we could compare their diet to the dietary habits of a healthy and growing population, it might help us better understand how we can steward and protect this vulnerable population.”
Historically, the rivers of Alaska, British Columbia, and the Pacific Northwest have provided salmon to resident killer whales.
But in recent years, humans have disrupted their food supply through water pollution, noise pollution, and building dams that cut off salmon’s migratory paths.
Additionally, humans started capturing resident killer whales, primarily southern whales and put them in amusement parks in the second half of the 20th century. This upset their social structure and reduced their numbers further.
The Alaska resident killer whale population has reached the thousands, while the northern resident killer whale population is continuing to experience steady growth.
Unfortunately, the southern resident killer whale population has stayed at around 75 individuals. Noise pollution from cargo ships and low birth rates are contributing factors to their small population size.
In the new study, the researchers collected fecal samples between 2011 and 2021 from southern resident and Alaska resident killer whales.
They analyzed the DNA from the samples and discovered that Alaska residents ate more chum and coho salmon in the summer. In contrast, the southern residents ate more Chinook.
Other fish featured in their diets include sablefish, arrowtooth flounder, Pacific halibut, big skate, and lingcod. Previously, it was thought that these whales ate only salmon. The two populations choose to eat different non-salmon species to supplement their diets.
Although protecting Chinook salmon populations is important for endangered southern resident killer whales, it is also just as critical to conserve the ecosystem of fish as a whole.
The study was published in Royal Society Open Science.
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