Elevated California sea lion beach strandings likely due to lack of food

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California sea lion pups are being stranded on beaches at high levels, and researchers believe a lack of food sources is contributing to the behavior.

The strandings, which were first noticed in January 2013, have been deemed an Unusual Mortality Event under criteria defined by the Marine Mammal Protection Act. They are unique because of their location and timing.

RELATED: Starving sea lion pups washing up on Southern California beaches (Chart)

The National Oceanic and Atmospheric Administration released updated data on Tuesday showing that 542 stranded California sea lion pups were admitted to rehabilitation facilities during the first five months of 2013. That number is more than three times the cases admitted in 2012. Many of the pups have been emaciated, dehydrated or underweight for their age.

The UME is still being investigated, but researchers said sardine spawning grounds shifted further offshore in 2012 and 2013. The food source is especially valuable for nursing mothers. While other prey species remained, those food items may not have been nutritious enough for adequate milk production or for newly weaned pups hunting on their own.

Disease has not been found to be a significant contributing factor to the increased strandings, though researchers are investigating the significance of the presence of one type of virus occurring in a high number of the samples.

The strandings are occurring in Los Angeles, Orange, Ventura, Santa Barbara and San Diego counties, but a NOAA information page says they may spread to northern counties in coming months. 

The agency says that treated pups have a high rate of survival. 

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