The goal of reducing sea lion predation on protected Columbia River basin salmon and steelhead stocks continues to be a moving target for fishery managers.

During the winter and spring of 2009, the fewest number -- 54 -- of California sea lions since 2002 were counted below the lower Columbia's Bonneville Dam, according to researchers. But on average each animal ate more salmon than ever recorded in the eight-year history of the study.

The Californian sea lions were joined by the largest number of Steller sea lions seen at the dam over the course of the study, and the Stellers also showed an increased appetite for salmonids this year.

As a result sea lions and harbor seals this year were observed eating more salmon than ever in the waters immediately below the dam, though just barely. The adjusted salmonid consumption estimate this year was 4,960 as compared to the previous high of 4,927 in 2008.

That total represented 2.7 percent of the salmon run this year, the lowest total since 2005. The size of the salmon and steelhead runs vary from year to year so a given level of take by predators will represent a different percentage of the run each year.

The consumption record was set despite the fact that 25 California sea lions, 11 last year and 14 this year, have been removed from the area by Oregon and Washington state trappers. Another California sea lion was trapped in August near the mouth of the Columbia at Astoria, Ore., and euthanized.

The Oct. 30 "2009 Field Report: Evaluation of Pinniped Predation on Adult Salmonids and other Fish in the Bonneville Tailrace" sums up U.S. Army Corps of Engineers research data compiled by observers stationed along the top of the dams two powerhouse and its spillway during daylight hours on weekdays. Regular observations began Jan. 14 this year and continued through May.

The study was launched as an attempt to better understand what impacts California sea lions, in particular, are having on salmon and steelhead stocks that are listed under the Endangered Species Act.

The California sea lions had not lingered below the dam in great numbers historically. It is believed that big salmon runs in 2000 and 2001 caught the sea lions attention and drew them to the 146 or so miles upriver to the dam. There they found and have feasted on concentrations of salmon looking for fish ladders so they can proceed upstream on their spawning run.

The pilgrimage has become an annual event. A total of 30 different California sea lions were identified in 2002, the first year of the study. The annual counts peaked at 104 and 99 in 2003 and 2004, and were in the 71-82 range from 2005 through 2008.

The vast majority of the fish are from hatcheries but a portion are naturally produced salmon and steelhead that are ESA-protected. The exclusively male California sea lion contingent is made up of individuals that forage north along the West Coast between breeding seasons on islands off the coast of Southern California.

Worried that sea lion predation could retard salmon recovery efforts, the states of Idaho, Oregon and Washington sought authority under the Marine Mammal Protection Act to lethally remove individually identifiable California sea lions that are preying on listed salmon. The California sea lions are protected under the MMPA but are not ESA-listed and the overall population is considered robust.

That authority was granted by NOAA Fisheries Service in March 2007. Legal challenges to the NOAA Fisheries Service decision are now being considered in the U.S. Court of Appeals for the Ninth Circuit after it was upheld late last year in U.S. District Court.

The decrease in California sea lion numbers this year is likely due to the removal of 11 individuals in 2008, the report says. The 14 removed this year are included in the 2009 head count.

An aggressive non-lethal "hazing" strategy was again employed in an attempt to deter predation on salmon below the dam. That hazing involved a combination of acoustic, visual, and tactile non-lethal deterrents, including boat chasing, above-water pyrotechnics (cracker shells, screamer shells or rockets), rubber bullets, rubber buckshot, and beanbags," according to the Corps' report.

Boat-based crews also used underwater percussive devices known as seal bombs. Dam-based and boat-based crews coordinated with Corps personnel, including the observers, to ensure safety and to increase the effectiveness of hazing efforts. Dam-based hazing by USDA Wildlife Services agents began on March 2 and was conducted seven days per week through the end of May.

Boat-based hazing was conducted by personnel from the Oregon and Washington departments of fish and wildlife and the Columbia River Inter-Tribal Fish Commission from the first week in January through May 15. Boats operated from the Bonneville Dam tailrace (river mile 146) downstream to Navigation Marker 85 (river mile 139).

"As in previous years, hazing activity temporarily moved some sea lions out of tailrace areas, but the animals typically returned and resumed foraging shortly after hazers left the area," according to the Corps report. "A slight shift to more predation occurring in the first and last hour of light during the day can be seen, which corresponds to hazing activities start and end times.

"The high adult salmonid and sturgeon consumption estimates seen in 2009 suggest that, at best, hazing at the current level of intensity only slows the increase of predation."

California sea lions were the primary salmonid predator again this year, accounting for 89.9 percent of the 2,980 observed catches. The "adjusted" predation total mentioned above includes estimates of fish caught by the pinnipeds when observers were not present and a portion of the observed catch of fish whose species could not be identified.

Despite the fact the California sea lion total dropped from 82 in 2008 to only 54 at the dam this year, they were considerably more voracious. They killed an average 74.3 salmon per sea lion over the course of the season. The highest "per capita" salmonid consumption previously had been 54.2; the average last year was 52.4.

The maximum number of salmonids taken by any individual California this year was 157, which is also a study record. The previous highs were 107 last year and 79 in 2006.

The larger Steller sea lions -- adult males average about 1,500 pounds and can weigh more than a ton -- visited the dam observation area in greater numbers this year. A total of 26 different Stellers were spotted compared to 17 last year and a previous high count of 10 in 2006.

The Stellers have in previous years shown a preference for white sturgeon and did again this year. They accounted for 95.1 percent or 721 of the 758 white sturgeon observed taken this year.

The observed white sturgeon catch by pinnipeds has risen each year from 265 in 2006, 360 in 2007 and 606 in 2008. The adjusted sturgeon consumption estimate is 1,710 for 2009.

Steller sea lion per capita consumption of salmonids was a record 18 in 2009. The previous high was 10 last year. Their overall adjusted estimated salmonid consumption was 475, for than double the previous high of 176 in 2008.

Chinook salmon were the most commonly identified prey species, making up 89 percent of the observed adult salmonid catch in 2009. Steelhead comprised about 11 percent of the observed adult salmonid catch.

The increased Steller consumption this year served to counter a slight reduction in the number of salmon eaten by the California sea lions. And the predation by Stellers could be taking a higher toll that the study numbers show.

"This year and last, Steller sea lions were often observed swallowing steelhead whole, suggesting that they could consume steelhead and jack Chinook entirely below the surface," according to the 2009 final report. "All consumption estimates provided are minimum estimates, but Steller sea lion predation may be significantly underestimated by surface observation techniques."

Many of the California sea lions present at the dam in 2009 have visited in the past, but 16 (30.2 percent of the total) were "new" additions to the "highly identifiable" pinniped list. The percentage of "new" California sea lions each year was 70.7 in 2003, 48.8 in 2004, 22.9 in 2005, 37.7 in 2006, 34.4 in 2007 and 33.8 in 2008.

"… we did not see a great increase in new individuals in 2009 replacing the animals removed," the report says. "In fact, 16 newly identified California sea lions was the fewest, matching 2005."

Three sea lions have been observed visiting the dam in all eight years of observation and were among the biggest salmon eaters. All three were trapped and removed this year.