Researchers were surprised seeing hundreds of sick and starving sea lion pups continuing to wash up on California beaches. As per researchers, 2015's figure of mass die-offs has been marked as the worst so far. Researchers have even asked the National Marine Fisheries Service to declare a rare unusual mortality event.

Researchers said they are still not known to the reason behind these increasing die-offs. But many scientists believe that warmer water has prompted the mother sea lions to go far into the sea in search of food.

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

More than 50 malnourished sea lion pups have been placed in a holding pen at Sea World San Diego since the beginning of the year after being rescued on beaches along the city's coast.

SeaWorld vet Dr. Hendrik Rollens said in a statement that when the pups were brought to the center, they were not in a condition to even raise their heads.

The National Oceanic and Atmospheric Administration said that despite the current situation, sea lions in California have been relatively healthy in recent decades, with the population at 300,000 today.