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.
The annual migration of some beluga whales in Alaska is altered by sea ice changes in the Arctic, while other belugas do not appear to be affected.
A new study led by the University of Washington finds that as Arctic sea ice takes longer to freeze up each fall due to climate change, one population of belugas mirrors that timing and delays its migration south by up to one month. In contrast, a different beluga population, also in Alaska, that migrates and feeds in the same areas doesn’t appear to have changed its migration timing with changes in sea ice.
The paper was published Dec. 21 in the journal Global Change Biology.
“The biggest take-home message is that belugas can respond relatively quickly to their changing environment, yet we can’t expect a uniform response across all beluga populations,” said lead author Donna Hauser, a postdoctoral researcher at the UW’s Polar Science Center.
“If we’re trying to understand how these species are going to respond to climate change, we should expect to see variability in the response across populations and across time,” Hauser said. “That may complicate our predictions for the future.”
Two genetically distinct beluga populations spend winters in the Bering Sea, then swim north in the early summer as sea ice melts and open water allows them passage into the Beaufort and Chukchi seas. There they feast all summer on fish and invertebrates before traveling back south in the fall. Other research suggests the whales are taught by their mothers when to migrate and which route to take, so it was unclear if belugas would be responsive to sea ice changes.