A new study nails dearth of chinook salmon as the primary cause of the endangered resident orca whale’s failure to rebound.
A team of researchers has isolated lack of food as the primary factor — bigger than vessel traffic, bigger than toxins — limiting recovery of resident killer whales.
In a paper published Thursday in PLOS ONE, a team lead by Sam Wasser, professor of biology and director of the Center for Conservation Biology at the University of Washington tracked the nutritional, physiological and reproductive health of southern resident killer whales — the J, K, and L pods of orcas that frequent the Salish Sea, including the San Juans and the waters of Seattle.
The study links low reproductive success of the whales, with a total population of just 78 animals, to stress caused by low or variable abundance of their favorite prey: chinook salmon.
Scientists continue to evaluate the role of vessel traffic, including whale-watch boats, toxins, and food supply in the orca’s troubles. Wasser said his results point to food as key.
“It’s the fish,” said Wasser, whose team found that of 35 pregnancies among whales tracked from 2007 to 2014, only 11 produced a live calf.
The females with failed pregnancies had levels of hormones indicating nutritional stress seven times higher than females that successfully gave birth.
“Pregnancy failure — likely brought on by poor nutrition — is the major constraining force on population growth,” Wasser said of resident orcas, a federally listed endangered species since 2005.
The number of pregnancies lost was actually probably higher: The team was unable to detect the earliest months of pregnancy, which is when failed pregnancies typically occur.
Deborah Giles, research director at the nonprofit Center for Whale Research, and an author of the paper, said vessel traffic and toxics and lack of food are all bad for the whales, but when whales are well-nourished, other problems don’t affect them as much. “If the whales are well-fed, you don’t see a strong signature for stress hormones related to vessels,” Giles said. “They are going through problems of famine and deeper famine.”
Some aren’t convinced lack of food is the orca’s biggest threat. “It is complicated,” said Brad Hanson, wildlife biologist with National Oceanic and Atmospheric Administration (NOAA) Fisheries, who has used acoustic sensors and tags to track the whales’ movements,…