An alarming number of sick and starving sea lion pups are turning up on California beaches this year, leaving scientists struggling to explain a third deadly winter for the pinnipeds.

This January, more than 250 emaciated sea lion pups were rescued.

"They just look very emaciated, very underweight. You can see the bones under their skin. You can get a visual of their ribs," said Erica Donnelly-Greenan, who manages the Sausalito-based Marine Mammal Center's rescue station along Monterey Bay.

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The cause of the problem isn't yet clear. Marine scientists say it may be warmer-than-average waters off the coast that are forcing mother sea lions in the Channel Islands to venture farther for food, leaving their young behind for too long.

"The pups are desperate and starving, so they just jump in the water and swim and get pulled to the coastline," Shawn Johnson, director of veterinary medicine at the Marine Mammal Center in Sausalito, told the San Francisco Chronicle.

Johnson said the pups are just too small and too weak to dive and catch fish.

Other explanations for the worrisome phenomenon include the possible accumulation of biotoxins in sea lions' prey populations as a result of algae blooms. Some scientists say over breeding could be at play, and the population is at carrying capacity.

NOAA is also studying whether the recent die-offs may be linked to changing ocean conditions or some other problem at sea. Disease is not thought to be the issue.

The sea lions at Marine Mammal Center's rehab facility in Sausalito are being nourished with herring, often force-fed with tubes when they can't ingest the fish on their own, and are being treated with antibiotics.

It will be several more months before most of them can be released back into the wild.

Tagssea lion, sea lion pups, starving sea lion pups, animal behavior, Ocean, animal starvation, Environment