A resident killer whale chasing a coho salmon to the surface. Image taken under permit.Candice Emmons/NOAA Fisheries
A team led by researchers at the University of Washington and the National Oceanic and Atmospheric Administration has uncovered key information about what resident killer whale populations are eating. Researchers had long known that resident killer whales - also known as resident orcas - prefer to hunt fish, particularly salmon. But some populations thrive, while others have struggled. Scientists have long sought to understand the role that diet plays in these divergent fates.
"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, UW assistant professor of aquatic and fishery sciences, who began this study as a postdoctoral researcher with NOAA's Northwest Fisheries Science Center. "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?"
In a paper published Sept. 18 in the journal Royal Society Open Science, Van Cise and her colleagues report the cuisine preferences of two resident killer whale populations: the Alaska residents and the southern residents, which reside primarily in the Salish Sea and off the coast of Washington, Oregon and northern California. The two populations show broad preference for salmon, particularly Chinook, chum and coho. But they differ in when they switch to hunting and eating different salmon species, as well as the other fish species they pursue to supplement their diets.
A resident killer whale chases a coho salmon to the surface. Often killer whales will reposition and "process" their prey near the surface, prior to tearing it apart and sharing with others in its group. Image taken under NOAA permit.Candice Emmons/NOAA Fisheries
Southern resident killer whales are critically endangered, while other populations are growing. This new study will inform conservation efforts for resident killer whales from northern California to the Gulf of Alaska.
"We know that lack of food is one of the main threats facing the endangered southern resident killer whales," said Van Cise. "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."
