More than 3,000 starving sea lion pups have washed up on California’s beaches since January—easily 15 times more than in a normal year.
“It’s unprecedented,” says Sarah Wilkin, national marine mammal stranding and emergency response coordinator for the National Oceanic and Atmospheric Administration.
And those are the lucky pups. The situation on California’s Channel Islands, where more than 90 percent of the U.S. sea lion population congregates to breed and nurse young, is even worse than in other parts of the state.
The influx of weak, sickly pups—3,110 as of May 20—has overwhelmed rehabilitation centers for the third year in a row. From San Diego to north of San Francisco, rescuers are busy retrieving pups (sometimes from city streets and oceanside bars), fattening up the ones that can be saved, and releasing them back into the sea [see video]. During the worst month, March, more than 1,000 pups rolled ashore, more than rescuers would normally see in an entire year.
Scientists blame this year’s stranding on a lack of food for the pups, courtesy of a warm water blob that has settled off the West Coast. But the reasons for the two previous mass stranding events, in 2013 and 2014, aren’t yet obvious. (See “Warming Pacific Makes for Increasingly Weird Ocean Life.”)
“We’re thinking it’s kind of the same root cause that keeps playing out, in that the animals are unable to find prey,” Wilkin says. “But the mechanism behind what is limiting the prey or keeping the prey away may have changed slightly over the three-year period.”
Hunting for Food
Most of the pups washing ashore this year were born in June 2014. Typically, sea lions stay with their mothers for about a year, nursing and learning how to catch fish on their own. But starting in January, droves of pups began leaving their island nurseries. Scientists suspect that’s because the sea lions’ normal food fish, such as sardines and anchovies, aren’t there.
When fish are scarce, mother sea lions have a hard time feeding their pups. Normally, nursing moms stay close to the Channel Island nurseries and only go on short foraging trips. But when the fish move away, those trips get longer and longer—so long that some waiting pups become hungry enough to take their chances on their own.
“The few pups that have enough strength to leave the rookeries and make it to the mainland get recorded as strandings,” says NOAA’s Mark Lowry, who monitors sea lion population numbers and also keeps track of what they’re eating. “There’s a lot of death out there.”
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