By Marty Graham
SAN DIEGO (Reuters) - A federal agency has declared that more sick and dying sea lion pups have stranded themselves on southern California beaches so far in 2013 than in the previous five years combined, but scientists are still unsure what is afflicting the mammals.
The "unusual mortality event" notice from the National Oceanographic and Atmospheric Administration (NOAA) released late on Wednesday follows animal rescue groups' warnings of a large influx of ailing sea lion pups in California.
"We anticipate this will get worse when the pups begin to wean from their mothers and have to forage on their own," said Sharon Melin, a wildlife biologist with the National Marine Fisheries Service, which is part of NOAA.
"It's going to be a bad year or two for sea lions," said Melin, who added that scientists were investigating what was causing the sea lions to get sick and die.
From the beginning of this year through last Sunday, 948 sea lion pups came ashore in Santa Barbara, Ventura, Los Angeles, Orange and San Diego counties, according to figures from NOAA.
Los Angeles County has seen the most strandings this year with 395, according to NOAA. In the previous five years more than 600 ailing sea lions came ashore, statistics showed. In all of 2012, there were 88 strandings.
The pups, which are born in the summer, usually stay with their mothers until April, Melin said.
"The oddest part of this is the pups should have been with their mothers," Melin said. "We think the mothers are having to go out farther and stay out longer to find food and the pups begin to forage on their own after they've been alone for some time."
But scientists remain unsure why the mother sea lions might be venturing out farther into the ocean.
The surviving pups are being taken to rehabilitation centers, including the SeaWorld San Diego facility, which has taken in 246 since January, according to SeaWorld spokesman Dave Koontz. SeaWorld had about 150 pups on Thursday.
"The vast majority are coming in malnourished and dehydrated, since they get their hydration from the fish they eat," Koontz said. "They stay with us three to four weeks or longer, until we get their weight up and then we return them to their habitat as soon as they are healthy enough."
Other centers are also swamped with the pups and many are at capacity, Melin said.
"There really isn't an oceanographic explanation for what we're seeing," Melin said. "We're looking at disease as a possibility and also at the food supply, and it could be some combination."
Melin said there were no signs of such distress in other marine mammals that rely on the same sardines, anchovies, squid and other fish. Nor are the adult sea lions dying at an unusual rate.
(Editing by Alex Dobuzinskis and Paul Simao)