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Stranded sea lion A juvenile sea lion sits on shore near the Huntington Beach Pier. (Rick Loomis / Los Angeles Times /March 31, 2013)

April 1, 2013, 2:32 p.m.

Federal marine wildlife officials said that a mass stranding of malnourished sea lion pups along the Southern California coast since January has intensified in recent weeks and researchers remain unsure of the cause.

Officials declared an "unusual mortality event" for the California sea lion, a designation that prompts immediate federal response after a significant die-off of a marine mammal population.

The declaration comes as sea lion pups have been found stranded on Southern California beaches -- from Santa Barbara to San Diego -- at rates exponentially higher than in years past.

In Los Angeles, for instance, nearly 400 pups have been stranded since the beginning of the year. Last year, just 36 were reported stranded.

As of March 24, officials said, 214 were reported stranded in San Diego County; 189 in Orange County; 108 in Santa Barbara County; and 42 in Ventura County.

The pups that survived have filled marine mammal sanctuaries along the coast, which have taken in record number of pups for this time of year.

The young pups have shown up lethargic and severely underweight, with their bones showing through their slick fur. It takes months of nursing to build up their health and their weight in order to be returned to the wild.

See the article here:

Sea lion pups washing up on SoCal beaches at alarming rate