Emily Chan
“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.
