Endangered killer whales that frequent the inland waters of Washington state are having pregnancy problems because they cannot find enough fish to eat, according to a new study. Researchers analyzed hormones in excrement collected at sea and found that more than two-thirds of orca pregnancies failed over a seven-year period. They linked those problems to nutritional stress brought on by a low supply of Chinook salmon, the whales' preferred diet, per the AP. "A large number of whales are conceiving, but when nutrition is poor, they don't sustain those pregnancies," says Sam Wasser, lead author of the paper and a biology professor at the University of Washington.
Southern resident killer whales along the West Coast have struggled since they were listed as an endangered species in 2005. They now number just 78, down from a high of 140 decades ago. The whales face threats from a lack of food, pollution, and boats. The new study, to be published in the journal PLOS ONE, zeroes in on food supply as an important stress factor among these fish-eating whales. Unlike other killer whales that eat marine mammals, the orcas that spend the summer in Puget Sound primarily eat salmon, mostly Chinook. Many species of Chinook salmon along West Coast are listed as threatened or endangered because of a host of factors, including loss of habitat from urban development, dams, fishing, pollution, and competition from non-native fish.