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Ecology and salmon related articles

Sea Lion Predation Down this Year

by Bill Rudolph
NW Fishletter, June 28, 2013

California sea lions consuming salmon just below the Columbia River's Bonneville Dam. (U.S. Corps of Engineers photo) According to the last weekly report on sea lion predation at Bonneville Dam, more California sea lions showed up than in 2012, but daily numbers were close to last year, which were the lowest observed since 2002.

The highest daily count was 21. About 60 different individuals were identified, and only 14 of those had been seen in previous years.

"Basically, a lot of new, smaller CSL [California sea lions] showed up to explore Bonneville throughout the season," said the May 16 report, which noted that they may have been attracted by the large smelt runs this spring, followed by the spring Chinook run. "Possibly either hazing or 'bullying' (by the larger Steller sea lions present) convinced them that they could catch fish elsewhere without having to endure harassment and theft of their catch."

Steller sea lion numbers were similar to 2011's high, and daily high counts were similar to 2010.

The report said estimated (non-adjusted) salmonid predation by California sea lions will be slightly higher than last year, "but similar to the lowest predation figures seen in 2002 and 2012."

The estimated salmonid predation by Stellers will be slightly lower than last year, but higher than all other years observed. Estimated sturgeon predation by Stellers will be the lowest seen since 2007.

Corps of Engineers biologist Robert Stansell said in his report that he had no idea why this occurred--"whether fewer sturgeon were present, or left earlier than normal, or SSL [Steller sea lions] decided to save room for the much more tasty spring Chinook!"

Bill Rudolph
Sea Lion Predation Down this Year
NW Fishletter, June 28, 2013

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