Categories: Science

Protected California Sea Lions Devour Threatened Salmon in Columbia River


Protected California sea lions are apparently gorging themselves on Chinook salmons and steelheads in the Columbia River, both of which are listed as threatened populations. Wildlife managers along the Columbia River in Washington and Oregon are facing a quandary. Sea lions have been congregating there for the past decade to feast on salmon waiting to climb the fish ladders at the base of the Bonneville Dam on their way to spawn each spring.

The Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) need protection, so much that the states of Washington and Oregon obtained permission from the National Oceanic and Atmospheric Administration in Silver Spring, Maryland, to kill the California sea lions (Zalophus californianus) feeding on the fish at the dam.

As a response, the Humane Society of the USA and other organizations filed a lawsuit to stop the practice. A district court in Portland is expected to hear the full arguments and issue a final ruling in the coming weeks. In the meantime, more than 40 California sea lions have been killed and 11 were transferred to aquaria and zoos.

Survey data collected by the US Army Corps of Engineers during the years of the cull show that the numbers of sea lions are decreasing, along with the amount of salmon they ingest. However, another predator seems to be ready to fill this gap left by the sea lions. In 2005, larger Steller sea lions (Eumetopias jubatus) arrived at the dam and have returned in greater numbers each year. Last year, they outnumbered California sea lions and ate half of the predated salmon.

Steller sea lions are also listed at threatened, so they cannot be killed. They can only be chased off. Their conservation status is under review to potentially remove this obstacle, but this won’t stop other predators from filling the void left in the ecosystem.

The Humane Society states that the culls focus on the wrong problems. Efforts should be made to reduce the allowable fishing catch, improve habitats and reduce losses from hydropower all of which are greater threats to the fish than sea lions.


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