In the first study of it’s kind, scientists have been able to analyse the diet of an endangered Killer Whale population based on fecal samples, with salmon showing to be their primary food source. Prior to this study, diet inference was primarily based on analysis of prey remains consumed by the whales at the surface, and it was uncertain if these were always representative of the total diet.
The study, conducted by Michael Ford from the National Marine Fisheries Service and colleagues, was published in open-access journal PLOS ONE earlier this month. The authors used genetic analysis of fecal material collected in their summer range in the Salish Sea in the Pacific Northwest, to estimate the diet composition of an endangered population of wild killer whales. They genetically sequenced 175 fecal samples collected from May to September from 2006-2011, which results in nearly 5 million individual sequences that they compared to potential fish from their diet.
They found that salmon made up >98% of the total sequences, which they inferred is the result of their diet. Of the six salmon species, Chinook salmon made up 80% of the sequences, followed by 15% coho salmon. They found that early in the summer their diet was dominated by Chinook salmon and coho salmon was greater than 40% in the late summer.
Estimating killer whale diet composition helps scientists understand interactions between predators and prey, but observing their diet directly is difficult. Killer whales appear to have an extremely diverse diet based on previous studies. Yet, individual ecotypes or populations are often extremely specialised, as in this case. In many parts of the world, killer whales prey on fishes or marine mammals, but not both. Killer whales have been observed preying on more than 140 species of animals, including many species of bony fish, sharks and rays, and 50 different species of marine mammals.
Killer whale populations in the North Pacific Ocean, the focus of this study, have been also been known to feed on species of squid (Gonatopsis borealis) and 22 other species of fish including rockfish (Sebastes spp.), Pacific halibut (Hippoglossus stenolepis) and Pacific herring (Clupea pallasi), in addition to salmon species.
Lead author Michael Ford adds:
“Using an independent method, we have confirmed that salmon, and especially Chinook salmon, are by far the dominant component of this whale population’s summer diet. The study helps to solidify our understanding of the ecology of this endangered population, and will be useful for continuing to prioritize recovery efforts.
- Michael J. Ford, Jennifer Hempelmann, M. Bradley Hanson, Katherine L. Ayres, Robin W. Baird, Candice K. Emmons, Jessica I. Lundin, Gregory S. Schorr, Samuel K. Wasser, Linda K. Park. Estimation of a Killer Whale (Orcinus orca) Population’s Diet Using Sequencing Analysis of DNA from Feces. PLOS ONE, 2016; 11 (1): e0144956 DOI:10.1371/journal.pone.0144956