Researchers from the University of Washington and the National Oceanic and Atmospheric Administration have conducted a study on the dietary habits of resident killer whale populations to better understand the differences in their ability to thrive. The study, published in the journal Royal Society Open Science, examined two populations of resident killer whales: the southern residents living in the Salish Sea and off the coast of Washington, British Columbia, Oregon, and northern California, and the Alaska residents. Both populations were found to have a broad preference for salmon, specifically Chinook, chum, and coho, but they differ in the timing of hunting different salmon species and the other fish species they consume to supplement their diets.
Southern resident killer whales are critically endangered, while the Alaska population is growing steadily. The researchers aimed to compare the dietary habits of these two populations to inform conservation efforts for resident killer whales from northern California to the Gulf of Alaska. Lack of food is one of the main threats facing the endangered southern resident killer whales, and understanding their diet compared to a healthy population could help better protect and steward the vulnerable group. The study sheds light on the impact of human activities on the resident killer whales, such as the pollution of waters, dam construction that reduces salmon runs, noise pollution interfering with hunting, and capturing whales for amusement parks, disrupting their social structure and reducing their numbers.
The team collected fecal samples from both southern resident and Alaska resident killer whales from 2011 to 2021 and analyzed DNA in the samples to determine their diet. They found that the summer diet of Alaska residents included more chum and coho salmon compared to the Chinook-heavy diet of southern resident killer whales. Additional non-salmon species found in the whales’ diets included sablefish, arrowtooth flounder, lingcod, Pacific halibut, and big skate, indicating a more diverse diet than previously thought. These dietary patterns vary between populations based on the abundance of different fish species regionally and the matriarch’s knowledge of reliable foraging locations, crucial for the survival of her family.
The study highlights the importance of protecting key populations of Chinook salmon to support the recovery of the endangered southern resident killer whale population but also emphasizes the need to take a more holistic approach to conserving the entire ecosystem of fish that contribute to the annual diet of predator populations like resident killer whales. The researchers believe that their findings and continued dietary studies can aid in the recovery of resident killer whale populations, particularly the very publicized struggle of the southern residents. Co-authors of the study include researchers from NOAA’s Northwest Fishery Science Center, the North Gulf Oceanic Society, and Lynker Technologies, with funding from various organizations including the National Fish and Wildlife Federation, Shell, SeaWorld, and the U.S. Marine Mammal Commission.