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Sequencing DNA from prey remains and fecal samples to reveal the diet of endangered Southern Resident killer whales. When the Southern Resident killer whale population was listed as endangered in 2005, there was considerable uncertainty about which threats may be responsible for the decline in the orca population. Along with the impact of vessel disturbance, underwater noise, and environmental contaminants, the availability of prey was identified as a risk factor.
In order to assess this risk, scientists in the Molecular Genetics program and Marine Mammal Program are working together to identify killer whale prey species and describe their overall diet. The investigations begin when marine mammal biologists locate and follow behind the killer whales in order to collect floating fish remains and whale feces off the water. Back in the NWFSC's genetics lab, scientists extract DNA from each sample. The DNA is sequenced to identify which fish species the whales had eaten.
Recently, researchers have employed cutting-edge "next-generation" DNA sequencing technology to look at thousands of DNA sequences obtained from the fecals samples. This method helps us determine the relative contributions of different prey species to the whale'’ overall diet. We have discovered that during the summer months when the whales are foraging in the Salish Sea, Chinook salmon make up a majority of their diet, roughly 80 percent.
While the fecal samples help our researchers understand the overall diet of this population of whales, the prey remains provide very detailed results. By identifying the unique genotype or "genetic fingerprint" of Chinook salmon prey remains and scales, scientists can determine which Chinook populations the whales feed on. We have found that of the Chinook consumed by the whales during the summer months, approximately 90 percent originated from the Frasier River in British Columbia.Publication:
Hanson, M.B., R.W. Baird, J.K.B. Ford, J. Hempelmann-Halos, D. M.Van Doornik, J.R. Candy, C. K. Emmons, G. S. Schorr, B. Gisborne, K. L. Ayres, S. K. Wasser, K. C. Balcomb, K. Balcomb-Bartok, J. G. Sneva, and M. J. Ford. 2010. Species and stock identification of prey consumed by endangered "southern resident" killer whales in their summer range. Endangered Species Research 11: 69-82.