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Bear Saliva: Scientists' New Source of Data

Nov 12, 2016 05:32 AM EST
Acquiring bear DNA from residual saliva left on salmon carcasses
Cynthia, a Kodiak bear enjoys an Atlantic salmon in Sydney, Australia. In the wild Kodiak bears normally live between 15 to 30 years. (Photo by Mark Metcalfe/Getty Images)

A new study has made waves in the scientific community by documenting the ability of researchers to gather bear DNA from residual saliva left on salmon carcasses, providing wildlife biologists with a new database. Published in the journal PLOS ONE, the scientists believe their study can provide a significant boost to research on the population and health of brown bears.

In their study, the researchers examined 156 partially consumed salmon carcasses of lakeshore-spawning sockeye salmon in the Chilkoot watershed and stream-spawning chum salmon at Herman Creek in the Klehini watershed. Both sites are near Haines, Alaska. They also swabbed a total of 272 brown bear "scats," or fecal samples, from those same locations.

"In the past, population estimates have been largely based on visual observations and on the analysis of fecal samples," stated Taal Levi, a co-author of the study. "We found that using bear saliva is not only easier and cheaper as a research tool, it is more effective."

Levi, an assistant professor of fisheries and wildlife at Oregon State University, and his colleagues found that the saliva collected from the salmon carcasses resulted in a higher rate of genotyping success. This not only allowed the researchers to identify individual bears more accurately and quickly than the fecal samples but also required significantly less effort.

"Bears love salmon because they are such a rich food source, and fortunately for us, the way they consume them lends itself to genetic monitoring," said the study's lead author, Rachel Wheat. A postdoctoral research associate at the State University of New York College of Environmental Science and Forestry, she conducted the research as part of her doctoral dissertation at the University of California, Santa Cruz.

"When salmon are plentiful, bears rarely eat the entire fish. In some cases, they only eat the brain, and we've found that swabbing along the edges of the braincase gives us the best results for extracting DNA," Wheat explained. "We also had success with swabbing inside distinct bite holes, and in the muscle tissue where the bears have stripped the skin off the salmon."

Of all the salmon carcasses sampled for saliva, the scientists got brown bear genotypes for 55 percent, a marked improvement over the 34 percent of the scat samples. Saliva sampling is also cheaper, costing only $118 as opposed to $370 per bear to genetically identify individual animals using scat samples.

"This advance will help allow us to more effectively, and more economically, study one of the largest bears on the planet," Wheat said.

Levi agreed and also noted that the method could be utilized outside bear research. It could be adapted to other species, as well. "Many predators leave saliva on food remains," he said. "We feel this type of saliva sampling could become an important tool for wildlife population monitoring."

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