Otter Decline Changes Eagle Habits

Over the last 15 years, the number of sea otters in Alaska's Aleutian Islands has plummeted, causing unexpected changes to the diet of bald eagles and the health of kelp forests.

Though eagles don't prey on adult otters, they eat the fish and sea otter pups that thrive in marine kelp forests. Otters eat sea urchins, which are the biggest threat to kelp forests. When otter numbers go down, sea urchin numbers go up, and kelp forests get destroyed.

Researchers discovered this complicated web of interrelationships while researching the sea otter decline, which they think was likely due to increased killer whale predation.

Though the population of bald eagles wasn't hurt by the shift, the lack of otters did necessitate a change in the eagles' habits.

"Bald eagles proved their extreme flexibility as a predator by simply shifting their diet to other available fish and seabirds when the sea otters were no longer present," said Robert Anthony, a USGS researcher with the Oregon Cooperative Fish & Wildlife Research Unit and lead author of the study. "Bald eagles are opportunistic feeders. They defend foraging territories against other bald eagles along these coastlines, and the terrestrial environment provides very little prey for them. So they forage over open water for most of their prey."

The researchers outlined their findings in the Oct. 10 issue of the journal Ecology.

--LiveScience Staff

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