Early action key to reducing sea lion impacts on salmon

Research uses epidemiological models to track spread of behavior among marine mammals

Date: December 16, 2016

Source: NOAA Fisheries West Coast Region

A new study used the same kind of models that scientists use to track disease to instead examine how some California sea lions have learned to prey on salmon gathering to ascend fish ladders at Bonneville Dam.

Although sea lions commonly feast on fish, their predation on salmon at Bonneville Dam on the Columbia River poses wildlife management challenges. The sea lions that gather on the Columbia each spring are protected by the Marine Mammal Protection Act while the salmon they are eating are protected by the Endangered Species Act.

In 2008 NOAA Fisheries authorized Oregon, Washington and Idaho wildlife authorities to begin trapping and removing sea lions shown to repeatedly prey on salmon at the dam. The removal program was designed to reduce impacts on protected salmon.

NOAA Fisheries recently authorized the states to continue the removals over the next five years.

The new study examined the effectiveness of the removal program, employing epidemiological models to assess how the behavior of eating salmon at the dam passes among sea lions. The research concluded that the removal program has successfully slowed the transmission of the behavior among sea lions, but would have been more effective if it had started sooner.

The findings highlight the need to act early "from both a conservation and management perspective to prevent the spread of a detrimental behavior and to minimize the total number of animals removed," the scientists wrote in the paper published in the journal Proceedings of the Royal Society B.

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