Pinniped Predation Report:  Hazing Not Reducing Sea Lions' Salmon Catch 

Columbia Basin Bulletin

April 11, 2008   

A total of 35,000 cracker shells, rubber bullets and seal bombs were fired off last year in what was a doubling of the effort to discourage sea lion predation on salmon and steelhead below the Columbia River 's Bonneville Dam.

But without the desired effect.

"Although hazing activity has noticeably altered the behavior of both California and Steller sea lions, total salmonid catch has not declined in response to hazing efforts," according to an April 2 report produced by U.S. Army Corps of Engineers researchers Sean C. Tackley, Robert J. Stansell and Karrie M. Gibbons.

The report, "Pinniped Predation on Adult Salmonids and Other Fish in the Bonneville Dam Tailrace, 2005-2007," details results of an ongoing study to evaluate sea lion eating habits, and impacts on spawning salmon and steelhead.

The report, dated April 2, can be found online at: http://www.nwd-wc.usace.army.mil/tmt/documents/fish/

The report does not make a recommendation regarding sea lion hazing, which began again this winter with renewed vigor.

"That's something we struggled with internally," Stansell said. Some of those involved say the effort should continue while others say it is a costly venture that doesn't seem to be reducing impacts on salmon and steelhead. A number of the passing fish are protected under the Endangered Species Act.

"It makes our job more difficult," Stansell said of the dam- and boat-based harassment of hunting California and Steller sea lions.

"The spillway became a kind of sea lion sanctuary in 2007, as full-time, intensive hazing efforts at PH1 and PH2 encouraged California sea lions to use the spillway tailrace," according to the report. "The spillway was extremely turbulent after April 10, which prevented boat access and limited the effectiveness of noise-based deterrents used by dam-based hazers." The dam's operators begin spilling water April 10 to facilitate downstream passage for juvenile salmon and steelhead.

"Observers reported that California sea lions became more secretive in response to hazing, spending more time below the surface than usual; making individual identification more difficult," the report says.

It would seem the hazing would have to continue in some form if the states Idaho , Oregon and Washington are to implement their newly won authorization to remove, lethally or otherwise, California sea lions that are having a significant negative impact on listed salmonid stocks. One of the conditions of that approval by the NOAA Fisheries Service says that animals can only be targeted if they are seen again below the dam after having been "subjected to active non-lethal deterrence."

The researchers have only been observing sea lion predation during the daylight hours, but this year they have done limited nighttime monitoring. A weekly report released Tuesday says that nighttime hunting has been both by California sea lions and Steller sea lions.

"This may explain why we see many animals only hauled out during the day and not hunting. Whether this is a result of daytime hazing activities, less dominant animals being pushed from daytime predation by larger numbers of dominant animals, or if it extends throughout the night has yet to be determined," the weekly report says.

Hazing efforts began in 2005 and have been stepped up in each of the succeeding springs, principally March through May.

Research carried out in 2006 indicated that hazing and acoustic deterrent efforts "failed to reduce the number of salmon taken or the total number of pinnipeds present at the project. Total observed salmonid catch was actually significantly higher on days with hazing and acoustics, but fewer pinnipeds were present within 100 feet of fishway entrances on those days.

There were no significant differences in salmonid catch or pinniped presence between days with or without boat-based hazing. Slightly fewer salmon were taken on days when boat hazing occurred, but more pinnipeds were present near the entrances," the 2005-2007 report says. "This may be because the boats had limited access and could not get too close to the dam, having the occasional effect of chasing some pinnipeds closer to the dam. Steller sea lions were responsive to hazing activities, and sturgeon predation in the study area was effectively halted when boat-based hazing began."

Stansell says that the Steller sea lions are not responding to the hazing this year as they have in the past.

The research has been ongoing since 2001, triggered by NOAA Fisheries' 2000 biological opinion on federal hydro system effects on listed salmon and steelhead. That document cited high rates of marine mammal tooth and claw abrasions on fish examined at the lower Snake River 's Lower Granite Dam adult trapping facility.

Few sea lions were noted as far upstream, 145 miles, as Bonneville until the turn of the century. Early in the decade their presence grew rapidly, numbering more than a 100 in the springs of 2003 and 2004. The spring California sea lion population has stabilized at about 80 in each of the past three years.

"Annual expanded estimates of pinniped predation on adult salmonids in the Bonneville Dam tailrace increased each year, from 2,920 fish in 2005 to 3,859 fish in 2007 ," the report says. "The relative impact, expressed as the estimated percentage of the salmonid run taken by pinnipeds, varied with run size and the expanded estimate of salmonid catch. The estimated percentage of the salmonid run taken by pinnipeds in the Bonneville Dam tailrace between 2005 and 2007 averaged 3.5 percent with a high of 4.2 percent in 2007."

Adult salmon and steelhead were the primary prey item, comprising at least 75.6 percent of observed catches. Pacific lamprey and white sturgeon were the second and third most commonly identified prey species, comprising 9.4 percent and 5.3 percent of total observed catch, respectively, according to the report. Chinook salmon are the mostly commonly identified prey of the sea lions.

California sea lions were the primary predator of adult salmonids in the Bonneville Dam tailrace, accounting for 99.0 percent of the 8,946 observed adult salmonid catches over the recent three-year period, and 99.8 percent of the 4,957 observed chinook salmon catches.

"About 91.4 percent of observed steelhead catches were attributed to California sea lions during this period, with Steller sea lions reportedly catching 8.5 percent of the total," the report says.

"White sturgeon was the most commonly observed prey item for Steller sea lions, which made 97.8 percent of the 626 observed sturgeon catches since 2002."

The report notes that "The sea lion season at Bonneville Dam has grown more protracted in recent years, as a few California sea lions and most Steller sea lions have arrived earlier each year. This increased predation activity prior to the mid-March through mid-June spring Chinook salmon run has resulted in increased impacts on steelhead and white sturgeon."

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