LOS ANGELES, Calif. -

Scientists say nearly half of all the sea lion pups born in island rookeries off Southern California this season have died and hundreds of starving pups are washing up on beaches between San Diego and Santa Barbara.

Wildlife biologists don't know whether the problem is food availability, disease or a combination of both.

It got so bad in the past two weeks that the National Oceanic and Atmospheric Administration declared an "unusual mortality event," which will allow more scientists to search for the cause.

Southern California rescue centers have become so overwhelmed they have had to start sending starving pups to Northern California.

And biologists say it is so bad on the beaches that rescuers have had to leave the worst of the pups behind while saving the strongest ones.