from UW Today, June 29, 2017. Note: Deborah Giles from the Center for Whale Research teaches the FHL 375: Marine Mammals of the Salish Sea course at Friday Harbor Labs in spring quarter.
A multi-year survey of the nutritional, physiological and reproductive health of endangered southern resident killer whales suggests that up to two-thirds of pregnancies failed in this population from 2007 to 2014. The study links this orca population’s low reproductive success to stress brought on by low or variable abundance of their most nutrient-rich prey, Chinook salmon.
The study, published June 29 in the journal PLOS ONE, was conducted by researchers from the Center for Conservation Biology at the University of Washington, along with partners at the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center and the Center for Whale Research. The team’s findings help resolve debate about which environmental stressors — food supply, pollutants or boat traffic — are most responsible for this struggling population’s ongoing decline.
“Based on our analysis of whale health and pregnancy over this seven-year period, we believe that a low abundance of salmon is the primary factor for low reproductive success among southern resident killer whales,” said lead author Sam Wasser, a UW professor of biology and director of the Center for Conservation Biology. “During years of low salmon abundance, we see hormonal signs that nutritional stress is setting in and more pregnancies fail, and this trend has become increasingly common in recent years.”
Southern resident killer whales typically feed from May to October in the Salish Sea, and spend winters in the open Pacific Ocean along the West Coast. Unlike transient orca populations that feed on marine mammals, more than 95 percent of the diet of southern resident orcas consists of salmon, with Chinook salmon alone making up about three-quarters of their total diet.