For months, the sea lion pups — not even a year old — have been washing up on Southern California beaches at an alarming rate. They were stranded, severely underweight, bones poking through their slick dark fur. They were clinging to life, many of them with ailments far beyond malnutrition.
The strandings, which began spiking in January, have intensified in recent weeks, packing marine mammal centers, perplexing researchers and prompting federal wildlife officials to act.
Officials last week declared an “unusual mortality event” for the California sea lion, a designation that came after the pups have been found stranded on beaches from Santa Barbara to San Diego at rates exponentially higher than in years past.
In Los Angeles County, nearly 400 pups have been stranded since the beginning of the year. Last year, 36 were reported during that stretch.
As of March 24, officials said, 214 sea lions were reported stranded in San Diego County, 189 in Orange County, 108 in Santa Barbara County and 42 in Ventura County.
Surviving pups have filled marine mammal sanctuaries along the coast, which have taken in a record number of sea lions for rehabilitation for this time of year. Sea World in San Diego has saved 270 sea lions, more than in the last two years combined. At last count, 170 sea lions were being treated there.
And in San Pedro, about 100 animals are being treated at the Marine Mammal Care Center, which has been overwhelmed. “It’s like we’re getting an entire year’s worth of cases in one quarter,” said David Bard, the center’s operations director.
So far in 2013, he said, the center has admitted more than 425 animals, “more than we see all year in most years.”
The onslaught has drained resources, requiring not just more food and medication but straining the pool of volunteers, who have to cover more hours and tend to more pups. The stays can last for months as they build up their health so they can be returned to the sea.
Bard said rescuers have been forced to prioritize so that the facilities have room for the most critically ill animals. They have cared for pups with injuries and abscesses, some that had seizures and some that had gotten tangled in fishing lines.
Bard said he hopes the federal designation will provide more funds for the center, allowing it to bring in more help.
Since 1991, federal wildlife officials have declared 57 unusual mortality events, including, most recently, for bottlenose dolphins in Texas in 2011 and 2012 and for North Alaska and Northeast pinnipeds in 2011.
The designation will also mobilize researchers — including biologists and oceanographers — to try to find an answer that has evaded others thus far.
Sharon Melin, a wildlife biologist with the National Marine Fisheries Service, said it’s not uncommon for sea lion pups to become stranded, but the recent occurrences have been troubling because of the scale, the time of year and the mystery surrounding their cause.
As more pups leave their mothers, Melin added, the problem isn’t likely to subside until summer.
“Usually, we know the problem,” she said. “We knew what was coming. When we saw the effect, we knew what it was caused by.”
Typically, that would be disease or warmer ocean temperatures, such as during an El Niño.
“What’s different about this incident,” she said, “is we don’t have any of that.”
The only anomaly, Melin said, is that these pups should still be with their mothers. The animals that have been found stranded were born over the summer and are about 6 to 8 months old.
The pups might have been left behind by mothers who had to venture farther out to sea to forage for food, forcing the young ones to leave the rookeries earlier and fend for themselves.
“They’re just not capable at this age,” Melin said. “They can’t dive deep, they’re not very efficient swimmers. They’re not old enough and big enough to be out on their own. They’re really naive and trying to make their way.”
Times staff writer Tony Perry in San Diego contributed to this story.