The elevated rate of gray whale strandings on the West Coast this year has prompted NOAA Fisheries to declare an unusual mortality event, triggering a scientific investigation into the cause of the strandings.
As of May 31, some 70 gray whales have been stranded on the coasts of Alaska, California, Oregon and Washington, the most since 2000, when more than 100 whales stranded in what was also determined to be an unusual mortality event. Federal authorities removed North Pacific gray whales from the endangered species list in 1994.
Additional gray whale strandings have been reported in British Columbia and Mexico. The eastern North Pacific gray whale population, which migrates along the Pacific Coast, was last estimated at about 27,000 animals.
“Many of the whales have been skinny and malnourished, and that suggests they may not have gotten enough to eat during their last feeding season in the Arctic,” NOAA Fisheries spokesman Michael Milstein said during a media conference call on May 31.
Gray whales feed on small crustaceans, including amphipods and can eat a ton a day of these shrimp-like amphipods. In years when ice in the Chukchi Sea melts late, the whales have a shorter feeding time because of lack of access to the feeding area, but with last year being unusually warm, the whales had access to the feeding area.
According to Sue Moore, a biological oceanographer at the University of Washington to participated in the conference call, scientists are wondering if the loss of sea ice last year led to a loss of algae that feed the amphipods.
“The sea ice has been changing very quickly over the last decade or so,” she said. “The whales may have to shift to other prey, such as krill or other things they eat.”
When more than 100 whales were stranded in 2000 a resulting investigation failed to identify why. That die-off came in the wake of strong changes in ocean conditions in the mid-1990s, which suggested that warmer water patterns affected the availability of prey, but researchers often were unable to perform necropsies, Moore said.
“It’s sometimes very difficult to get to these whales in a timely fashion,” she said. “You can’t always get the kinds of samples you would need for diagnostic reasons.”
Deborah Fauquier, veterinary medical officer at NOAA’s Office of Protected Resources, said that since 2000 researchers have enlisted a better network of volunteers and also better educated the public to help report and respond to the deaths of whales. This year scientists have been able to perform necropsies on 20 of the whales, she said.
Research biologist John Calambokidis of the Cascadia Research Collective, also noted that whales compelled to search away from the areas where they traditionally feed they have turned up in places like San Francisco Bay and Puget Sound, where they are at higher risk of getting entangled in fishing gear or struck by ships.
The Associated Press contributed to this story.