Guadalupe fur seals, a threatened species found off the coast of Southern California and Mexico, are experiencing an “unusual mortality event,” the National Oceanic and Atmospheric Administration announced this week. NOAA defines an unusual mortality event as “a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response.”
Since January, approximately 80 seals have been found stranded along the shore of central California — about eight times more than is usual for the species. Over the past 20 years, there have been an average of just 10 to 12 Guadalupe fur seal strandings per year. Out of the 80 this year, 38 of the seals were alive and 42 were found dead, said Justin Viezbicke, NOAA Fisheries Stranding Coordinator for the West Coast Region, during a teleconference Tuesday afternoon.
The majority of the stranded seals are pups that were born in 2014, said Tenaya Norris, a marine scientist at The Marine Mammal Center in Sausalito, Calif., during the teleconference. The Marine Mammal Center is one of two institutions officially charged with rehabilitating stranded Guadalupe fur seals — the other is SeaWorld.
All of the stranded seals, both alive and dead, were found severely emaciated. Scientists suspect that the mortality event is connected to unusually warm conditions in the eastern Pacific, which have persisted for about two years now, said Toby Garfield, director of the environmental research division at NOAA Southwest Fisheries Science Center, during the teleconference. These conditions have been caused by a warm-water “blob” and an associated high-pressure ridge in the gulf of Alaska, he said, which have changed weather patterns in the region and caused anomalously warm conditions along the West Coast.
“We think that warm water conditions have really changed the range of quite a few of the forage fish species that the fur seals would be going after,” Garfield said. Some of the fish species that seals usually eat have moved farther north to escape the unusually warm waters, while other species that are usually found south of the seal’s range have started moving into the region. These changes in the seals’ available food sources could be causing the emaciation that scientists are witnessing in the stranded animals. The same warm-water conditions are likely tied to the only other unusual mortality event announced this year, which NOAA declared for large whales, including fin whales and humpbacks, last month.
The die-off could be a big problem for the Guadalupe fur seal, which has been listed as threatened under the Endangered Species Act since 1967 and is also protected by the Marine Mammal Protection Act. According to NOAA, the species was hunted to near extinction in the late 19th century and now numbers at about 15,000 individuals, thanks to recovery efforts. The seal has a highly limited geographic range, and it breeds almost exclusively on Guadalupe Island, off the coast of Baja California, Mexico.
While 80 strandings out of a population of 15,000 might not sound like much, Viezbicke cautioned that there are probably more suffering individuals out at sea that just haven’t been observed. “We’re assuming there are others out there in the same boat as these guys — we’re just not seeing them,” he said.
And since the fur seal remains a threatened species, scientists will be keeping a close eye on them in the coming months. “At this point there will be no additional protections [placed on the Guadalupe fur seal], but we will be increasing our attention,” Viezbicke said, adding that “we have a working group, experts from all around the country, that are weighing in.”
Coincidentally, an unusual mortality event has been ongoing for California sea lions since 2013, although Viezbicke said the number of strandings for that species are gradually returning to normal. Scientists believe the mortality events for the California sea lion and the Guadalupe fur seals could be linked to the same unusually warm conditions that are ongoing in the eastern Pacific.
