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NW Fishletter #341 January 15, 2015

[3] Sea Lion Numbers Growing In Lower Columbia

Oregon and Washington fish managers say that robust smelt runs over the past couple of years are likely responsible for attracting more California sea lions to the lower Columbia River. They said that nearly 1,500 sea lions were estimated in the region at the spring peak in 2014, and about 750 in 2013. For the eight years before that, the spring peak total ranged between 200 and 350 individuals.

Robin Brown and Bryan Wright of the Oregon Department of Fish and Wildlife, and Steve Jeffries of the Washington Department of Fish and Wildlife, reported their latest estimates at the Jan. 13 meeting of the Northwest Power and Conservation Council's F&W committee. Members had asked for the update last fall, after hearing a troubling report that laid out a circumstantial case for heavy predation by marine mammals in the lower river from Astoria-based NOAA Fisheries researcher Michelle Wargo Rub. Her results suggested that the mortality from predation might be much higher than the 2 percent estimated near the dam itself.

In 2014, Wargo Rub reported that her preliminary findings from PIT-tagging adults in the estuary showed that Chinook survival to the dam was about 40 percent through April 7, then above 60 percent through May 2, and more than 80 percent through June 20, when river temperatures were much higher. If the results were taken at "face value," and applied to the run at large, she said it implied that 35,000 to 99,000 fish annually have returned to the river, but dropped out of the system before they got to Bonneville Dam.

Wargo Rub said last November that estimates from 2010 had pegged about 7,000 pinnipeds in the near ocean and lower Columbia region, made up of 3,000 sea lions and 4,000 harbor seals.

After her presentation last November, Doug Hatch, senior fisheries scientist with the Columbia River Inter-Tribal Fish Commission, said 600 to 700 California sea lions had been counted in a single spring day during a boat survey from the dam to Astoria in 2014.

The managers also expressed concern over increasing predation by the California sea lions at Willamette Falls, where they estimated more than two dozen of them had consumed 13 percent of the Willamette's ESA-listed steelhead run and 8 percent of the ESA-listed spring Chinook run in 2014.

Meanwhile, near Bonneville Dam, Steller sea lions had begun to outnumber the Californias since 2009, but the agencies have no authority to lethally remove Stellers. Fifteen individual California sea lions were lethally removed in 2014 from the area after heavy predation on spring Chinook had been documented by agency personnel.

The managers said both adult salmon and sea lions will be radio-tagged this year to get a better picture of what is really happening in the lower river. -B. R.

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