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Research Analyzes which Salmon
Hit Hardest by Sea Lions and Seals

by Columbia Basin Bulletin
Chinook Observer, January 3, 2008

(CHINOOK OBSERVER COLLECTION) The war between fishermen and marine mammals is an old one: A 1915 postcard shows a dead 900-pound sea lion posed with a salmon on the waterfront in Ilwaco. COLUMBIA RIVER - Does sea lion predation in the Columbia River have a greater impact on some stocks, including protected species, than others?

Yes, and it's all in the timing, according research undertaken this year by the University of Idaho in cooperation with the U.S. Army Corps of Engineers.

"Early timed stocks are at greater risk" overall, according to Matthew Keefer, who led the comparison of sea lion abundance and predation data at Bonneville Dam with stock-specific adult spring Chinook salmon abundance and timing estimates from ongoing radiotelemetry and PIT-tag studies. The UI's Christopher Peery and Michael Jepson and the Corps' Robert Stansell also contributed to the analysis.

Keefer presented the results of the analysis in December during the Corps' Anadromous Fish Evaluation Program annual review in Walla Walla. AFEP funds evaluation and monitoring studies designed to give the region better biological information and insights related to fish passage and survival at hydropower dams.

Previewed were preliminary results research regarding juvenile and adult fish passage, including lamprey; fish transport and delayed mortality; estuary studies; bull trout studies; and avian and pinniped predation.

Predation rapidly increasing at dam

Over the past seven or eight years, California sea lions' presence at Bonneville has grown from a handful to as many as 80 to 100 in recent years during the late winter and spring. Corps' research shows that the pinnipeds' predation on steelhead and, particularly, upriver spring Chinook salmon has increased from 0.3 percent of the salmonid run passing Bonneville in 2002 to an estimated 4.1 percent in he spring of 2007. The prey includes Upper Columbia and Snake River spring Chinook salmon that are listed under the Endangered Species.

The Corps asked for the UI analysis because "we wanted to see if there were any differential effects on stocks," according to Dave Clugston.

Analysis of data generated from telemetry studies showed early stocks were consistently from the Salmon (Little Salmon), Clearwater (South Fork, Lolo Creek, Lochsa) and Icicle River drainages, according to an abstract of the analysis. Of PIT-tagged groups, the earliest wild stocks were from the Clearwater, Yakima and John Day basins and the earliest hatchery stocks were from Carson, Leavenworth, Dworshak and Rapid River hatcheries.

The analysis involved generating week-by-week stock composition estimates for the spring Chinook runs in 2002-2007 and comparing them with pinniped consumption patterns.

The abstract used as an example the result that about 18 percent of the Chinook eaten by sea lions in 2002 were from the Clearwater basin.

"Some populations are dominant in any given week," Keefer said of the 34 or so stock segments that comprise the spring Chinook species.

A second analysis estimated impacts on individual populations between years. It showed, as another example, that impacts on Little Salmon River spring Chinook ranged from 0.6 percent in 2002 to 7.3 percent in 2005. In 2007 there was almost a 10-fold difference between the most highly impacted populations and those least impacted by sea lion predation.

The analysis showed that impacts can vary from year to year, and within years. It's all in the timing - of a particular stock's spawning run and the sea lions' presence.

Mixed results for harassment efforts

The sea lion-salmon issue has raised considerable concern and action. Last year a sunup-to-sundown effort was launched to harass the marine mammals, and potentially shoo them away from the Bonneville trough, where salmon are easy targets while they meander, looking for an upriver passage route.

Massive grates, called Sea Lion Exclusion Devices (SLED), were installed in the winter of 2006 at the entrances to the dam's fish ladders. The intent is to prevent the sea lions from entering the ladders while allowing the salmon continue on their journey.

Two years of relatively late-timed runs prompted concerns that the sea lion hazing and/or the SLEDs could be daunting salmon. A related evaluation by the UI indicates that likely shouldn't be a concern.

"Although some salmon behaviors appeared to change in response to the deterrents, salmon passage times with the deterrents were comparable to passage times in other years and fishway exit rates appeared to be lower with deterrents," according to the abstract. The latter data may suggest that the fish are hurrying to get away from the sea lions.

During his presentation of the Corps predation study's 2007 findings Wednesday, Stansell said that the sea lions are coming upriver earlier each year, and more of the marine mammals are settling in for longer periods.

"They're coming up to Bonneville and staying. There's no reason to depart," Stansell said. The salmon represent a quick and easy food supply for pinnipeds fattening up before their summer breeding season. Observers on the dam deployed for the study saw 3,859 salmonids taken by sea lions between Jan. 9 and May 26 this year.

Overall, 44.7 percent of the prey taken were positively identified as Chinook and another 29.5 percent were judged to be salmonids, either salmon or steelhead. Lamprey made up 9.3 percent of the observed sea lion catch.

White sturgeon take, primarily by Steller sea lions, has also increased, particularly in the past few years. Stansell said sturgeon kills in 2007 probably made up about 10 percent of the pinnipeds total observed prey.

The hazing has changed the California sea lions prey strategy, but not dulled their appetite.

The rubber bullets, cracker shells, seal bombs and other tools make the California sea lions "more skittish, makes them dive under water," Stansell said. But they continue to hunt, some moving to the turbulent area's below Bonneville's spill gates where the hazers can't follow.

"Harassment efforts may be pushing predation more toward night," as well, Stansell said. The pinnipeds were not believed previously to do much foraging during the dark hours.

For more information about 2007's AFEP review and to view research abstracts go to (

Columbia Basin Bulletin
Research Analyzes which Salmon Hit Hardest by Sea Lions and Seals
Chinook Observer, January 3, 2008

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