Starving sea lion pups are washing up all along the Southern California coast in unprecedented numbers, and scientists don’t know why.

As of March 24, 948 babies have washed ashore this year in Santa Barbara, Ventura, Los Angeles and San Diego counties, compared to 88 all of last year. Less than 700 were stranded in the five years previous combined.

The babies are undernourished, underweight and dying at unexpectedly high rates. Rescue facilities are overwhelmed and have begun shipping the pups to centers in Northern California. Scientists have begun tests to see if the problem is disease, lack of food or both.

The National Oceanic and Atmospheric Administration (NOAA) has declared the situation an Unusual Mortality Event (UME). The agency has declared only 57 UMEs in the U.S. since 1991.

So far, adult sea lions do not seem affected by whatever is causing the problem. Scientists are also studying the condition of other marine mammals that rely on the same food as sea lions—squid, sardines, anchovies—but have not found them suffering.

The babies, which are usually born in the summer and stay with their mothers until April, may have become separated when the adult ventured farther out to sea in search of food. But that is just speculation by scientists, who are baffled by why mother and child would separate before weaning is finished.

California sea lions range from the Pacific coast of Central Mexico to British Columbia, Canada. The estimated population of California sea lions as of 2011 was 296,750, with an annual increase of 5.4%. The main breeding areas are are on islands located in Southern California, western Baja California and the Gulf of California.  

It is suspected that whatever is affecting the Southern California pups will eventually be felt elsewhere.

“It's going to be a bad year or two for sea lions,” Sharon Melin, a wildlife biologist with the National Marine Fisheries Service,” told Reuters.  

–Ken Broder

To Learn More:

Starving Sea Lion Pups Fill Calif. Rescue Centers (by Sue Manning, Associated Press)

Stranded Sea Lion Pups Arrive in Northern California (by Nadia Drake, Wired)

Sea Lion Pups Dying at High Rate in California (by Marty Graham, Reuters)

2013 California Sea Lion Unusual Mortality Event in California (NOAA Fisheries)

FAQs on the California Sea Lion UME in California (NOAA Fisheries)