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Molting Seals Boost Mercury Levels In Coastal Ecosystems

Photo credit: C.V. Vick/Flickr

Elephant seals gather at Año Nuevo State Park, June 5, 2007.

Marine mammals don't just stink up areas like La Jolla Cove. According to a new study, they're also elevating mercury levels in these ecosystems.

Marine mammals are known for being a bit of a nuisance in San Diego, blocking beach access and creating foul smells at La Jolla Cove.

A new study finds seals and sea lions also contribute to a different kind of nuisance: high mercury levels in coastal ecosystems.

Scientists know that mercury accumulates as it moves up the food chain, causing sea lions and seals to consume a lot of it.

"We wanted to take it a step further," said San Diego State University graduate student Jenn Cossaboon, first author on the study.

"We wanted to see what happens when it reaches those apex predators. The contaminant doesn't stop there, since mercury never fully breaks down."

It turns out marine mammals shed a lot of mercury too. The researchers analyzed hair samples from elephant seals at Año Nuevo State Park near Santa Cruz. They found that waters surrounding Año Nuevo contained 17 times more neurotoxic methylmercury during molting season than coastal sites free of seals.

More research would be needed to understand the extent of mercury pollution from marine mammals in San Diego, but Cossaboon suspects places like La Jolla Cove may have similar problems.

"Anywhere there are a lot of seals or sea lions that are eating and defecating and molting, I would say it would be something worth looking into," she said. "There's a good chance mercury would be elevated."

Cossaboon says she'd also be interested in studying larger rookeries at islands off of Southern California, like San Nicolas and San Miguel.

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