Feasting sea otters help reduce erosion, study says

Photo: A sea otter in the estuarine water of Elkhorn Slough, Monterey Bay, California. (Emma Levy via Courthouse News)

The return of top predators like otters can help ecosystems, scientists say.

After nearing extinction, sea otters are returning to California’s Monterey Bay — and they’ve brought their appetites. That’s great news not just for the otters, but also for the environment and humans alike, according to a new study.

Otters once filled the waters from Russia and Japan in the east, to along the West Coast of the U.S. and down to Baja California, but demand for their soft fur in the 18th and 19th centuries drove a hunting frenzy that left a population of only 50 survivors in California, said Brent Hughes, an associate professor of biology at Sonoma State University, and the lead author of the study, published in Nature on Wednesday. 

Due to their absences in California’s Monterey Bay, shore crabs, the otter’s prey, were left to burrow along creek banks and salt marshes in peace, eating the roots of marsh plants, which led to erosion. Combined with the pressures of the growth of land development along the shoreline, nearby agricultural industry and rising sea levels, the rapidly eroding marshes affected wildlife and their ecosystems. 

But then the otters returned. 

Thanks to conservation laws and a successful otter pup surrogacy program at the Monterey Bay Aquarium, California’s otters began to repopulate the coast in the 1980s. 

The new study looks at the effect of that repopulation on one specific area — Elkhorn Slough in Monterey Bay along California’s Central Coast — and how the otters’ appetite for crab has slowed the erosion of creek banks and marshes.

“It would cost tens of millions of dollars for humans to rebuild these creek banks and restore these marshes. The sea otters are stabilizing them for free in exchange for an all-you-can-eat crab feast,” Brian Silliman, a Rachel Carson distinguished professor of marine conservation biology at Duke University and one of the study’s senior authors, said in a press release.

Because otters eat about 25% of their body weight in food every day — around 22 pounds of food — their ravenous hunger caused […]

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