A mass stranding of malnourished sea lion pups along the Southern California coast that began in January has intensified in recent weeks, officials said. Federal marine wildlife officials have declared an \"unusual mortality event\" for the California sea lion, the Los Angeles Times reported Tuesday. The designation requires immediate federal response to a significant die-off of a marine mammal population, the newspaper said. The numbers of sea lion pups found stranded on Southern California beaches this year has been higher than in years past with marine mammal sanctuaries reporting a record number of pups for this time of year. Most of the stranded pups have been lethargic and underweight, officials said, and will require months of care before being healthy enough to return to the wild, sanctuary workers said. As of March 24, officials said, 400 pups have been stranded in Los Angeles County; 214 in San Diego County; 189 in Orange County; 108 in Santa Barbara County and 42 in Ventura County.