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What is killing California sea lion pups? Why unusual event is a concern (+video)

Scientists say the sea lions reveal 'important things about what is going on in our oceans.' Food shortages and disease are being looked at as possible causes of the 'unusual mortality event' in California.

Why are California sea lions dying?
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California’s sea lions, usually celebrated for their entertaining, prankster ways and doglike barks, are making very different headlines right now. Young pups are washing up dehydrated and dying, from Monterey to San Diego, in record numbers.

So far, more than 1,100 of these emaciated, underweight marine mammals have come ashore – more than ten times the normal rate for this time of year. As startled residents cope with these sickly animals on local beaches, overwhelming marine mammal rescue facilities, scientists are scrambling to decipher the mysterious message behind these strandings.

“We do not know the cause,” says Sharon Melin, a marine biologist at the National Oceanic and Atmospheric Administration (NOAA).

NOAA has taken the extraordinary step of declaring an “unusual mortality event,” or UME, which brings with it additional funds for research as well as national collaboration between agencies.

One recipient of that additional UME funding is the Pacific Marine Mammal Center in Laguna Beach, an hour south of Los Angeles. Development director Melissa Sciacca says they knew as early as January they were facing an unprecedented event.

“We began seeing 10 to 12 animals every day coming into the facility,” she says, noting that this began during a time when even a single young sea lion beaching is unusual. Sea lion pups don’t typically wean until April or May, and while a certain number of pups fail to thrive annually, she adds, it has never been at this rate.

“In our 42 years, we have never seen anything like this,” she says.

At this early stage, scientists are focusing on food shortages and disease as possible causes, says Dr. Melin. While some have raised the possibility of radiation effects from the Fukushima earthquake in Japan, Melin points out that this event is narrowly limited to the young sea lion population.


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