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Corps Study Documents
Pinniped Predation at Bonneville Dam

by Barry Espenson
Columbia Basin Bulletin - June 18, 2004

The number of sea lions and other pinnipeds making the 140-mile journey from Pacific Ocean to the base of Bonneville Dam seems to have leveled off this spring after having more than tripled from 2002 to 2003

That leveling occurred, however, at a high number relative to the past.

The hungry mammals did stay longer this year and exacted twice the toll, relatively, on migrating salmon and steelhead than they did last year, according to preliminary data released recently by the U.S. Army Corps of Engineers. Researchers estimate that California sea lions ate 2.1 percent of the salmon and steelhead passing the dam from Jan. 1 through May 31.

The bulk of that salmonid consumption -- 2 percent -- came between March 15 to May 31 as upriver spring chinook made their way toward hatcheries and tributary spawning grounds. That compares to an estimated 1.1 percent of the 2003 salmonid run taken last year and 0.3 percent in 2002, the first year of the study.

The favored foodstuffs for the California sea lions, and a handful of harbor seals and stellar sea lions, are the chinook and steelhead. Researchers witnessed the taking of 451 chinook and 352 "unknown salmonoids" as well as 25 steelhead, 119 lamprey and 20 shad. The unknown category is for fish observers couldn't positively identify but what were most likely chinook.

"It's predominately chinook," Robert Stansell, the Corps' project leader for the study, said of the lions' fish consumption. The study was undertaken in 2002 and 2003 at the direction of NOAA Fisheries' 2000 Federal Columbia River Power System biological opinion. That document evaluated the jeopardy posed by the federally hydrosystem to salmon and steelhead listed under the Endangered Species Act. It called for an evaluation of "pinniped" impacts at Bonneville on the listed fish.

And while the full study was not funded this year, a scaled-back observation was undertaken by Corps staff. During that March through May period researchers spent four hours per day, five days per week observing pinniped activities below the dam. The total hours spent observing the animals at the three tailraces this year was 553, compared to 1,440 hours last year.

The researchers actually observed 838 salmonids being caught and eaten by the mammals. That number was expanded to an estimated 3,872 salmonids that the researchers believe were consumed over the entire time period. That compares to a 2,394-salmonid estimate last year from what was a larger run. The total number of salmonids passing Bonneville this year during the period was 184,141 compared to 217,869 last year.

California sea lions were consistently present beginning Feb. 22 this year, three weeks earlier than in 2003. They were last seen on May 26. The sea lions are mostly males that swim north in late summer from breeding and calving grounds on, for the most part, islands off the coast of California and Mexico. Their increased presence in the Columbia River coincides roughly with an upturn in the fortunes of Columbia/Snake upriver spring chinook. After lingering at depressed levels for the past few decades, the upriver spring chinook rose to record levels in 2001. Returns from 2000-2004 have all been strong compared to those of the 1980s and 1990s.

Biologists have theorized that the sea lions had first been attracted to the Columbia by returning smelt. Then they seem to have seized on the opportunity of feeding on, and following upriver, the spring chinook. Now, with the upriver run dwindled and June-July sea lion breeding season upon them, the animals have moved south.

Bonneville is the first hurdle the migrating salmon face on their spawning journey. As they hesitate, searching for a passage route, the fish are easy pickings for the lions in the tailraces below the dam's two powerhouses and its spill bays.

The California sea lions, called both intelligent and "opportunistic," have found a good thing. Sea lions were seen at the dam only occasionally in recent decades, and in few numbers, prior to 2001.

Then all of a sudden in 2002 at least 30 individual sea lions (and as many as 36) were observed spending the late March to mid-May period below the dam. That number soared to 106 last year. The count this year was 100 individuals.

The statistics for the past three years show that the upriver journey has become at least a short-term habitat. About half of this year's visitors were repeaters, having also made the journey in previous years.

The BiOp that called for an evaluation of pinniped predation at the dam is now being rewritten as part of a court-ordered remand process. That 2000 BiOp declared that hydrosystem actions jeopardized the survival of eight of the 12 listed Columbia basin salmon and steelhead stocks. The document included a "reasonable and prudent alternative" that outlined actions to improve survival and investigate areas of concern, such a predation, where hydro operations may be in some measure responsible.

"We weren't just putting things in there out of curiosity," said Gary Fredricks of NOAA Fisheries' Northwest region hydro branch said of the predation study. The fact that fish mortality is occurring at the foot of the dam is obvious. The hydrosystem's share of the blame, however, is hard to calculate, he said.

"It's predation and it's happened on the river forever," Fredricks said. The "jeopardy analysis" that is to be conducted during the next few months will predicate what, if anything, will be done at the dam to reduce fish mortality. If the analysis says there is no jeopardy, no RPA will be required. If there is jeopardy, structures may be considered along that scrimmage line immediately below the dam that will allow fish through but exclude the sea lions.

"If there is a jeopardy call I would try to push that through the opinion process," Fredricks said. The fish are confused, and as a result more vulnerable, as they encounter their first dam.

"They've got a blockage in front of them and sea lions behind them," Fredricks said. The construction of such exclusion devices would likely allow more adult fish to find entrances to the passage system and, ultimately, complete their spawning journey. That could eventually help populations as their progeny emerge in greater numbers to start a new life cycle. But it would not calm the jitters of lower river sport and commercial fishers.

Throughout the spring fishers have remarked at both the number sea lions in the river and their boldness. Reports have sea lions literally taking salmon off hooks and out of gill nets.

"I've heard from more people this year, both sport and commercial, than I have in any other year," said Cindy LeFleur, the Washington Department of Fish and Wildlife's Columbia River policy coordinator. She's been involved in Columbia mainstem fishery management for more than 10 years. Those reports, some on sea lion thievery and others merely on the mammals' presence, have come in from the entire length of the river below Bonneville.

Individual gill-net fishers and anglers, during Columbia River Compact and mainstem sport hearings, have insisted that something must be done to reduce sea lion impacts on the salmon run. Sport and commercial fisheries have only been revived during recent years' abundant run but continue to be limited by measures intended to protect ESA-listed upriver spring chinook.

"Doing something" such as removing sea lions, lethally or otherwise, is not so easily done. Nor is it necessarily desirable. Numbers of California sea lions and other pinnipeds had sunk to perilously low numbers by the early 1970s, creating the need for the federal Marine Mammal Protection Act. The California sea lions have since bounced back dramatically with the population growing at an annual rate of from 5.4 to 6.1 percent since the late 1970s, according to a population status report updated in February 2003 by NOAA Fisheries.

But NOAA Fisheries has yet to determine that the population has reached its "optimal sustainable population" level, a goal mandated in the MMPA. The act allows deterrence of sea lions by sport and commercial anglers that do not cause physical harm to the animals. But the process is long and painstaking to provide the justification necessary for a permit to actually remove individual sea lions from a locale, according to Brent Norberg, head of marine mammal division for NOAA's Northwest region.

The agency made recommendations to Congress in the late 1990s for a streamlining of that permit process but "none of those recommendations have been acted on," Norberg said. Congress has yet to undertake the full-fledged reauthorization of the MMPA that the law requires.

Steve Fick, owner of fish processing facilities and member of Salmon for All, acknowledge that there has always been some bad blood between commercial fishers and the animals that can damage fishing equipment and compete for a limited fish resource. But the sea lions seem more numerous, and troublesme, than ever this year.

"It seems like there is increased predation this year," Fick said. The clever animals are seizing the opportunity, he said.

Liz Hamilton, an avid angler and executive director of the Northwest Sportfishing Industry Association, points to Bonneville.

"We're kind of setting the table for these brilliant, opportunistic creatures," Hamilton said of sea lions who followed the run upriver, found a feast, remembered it and brought back friends the next year.

"They tend to be a scapegoat for a lot of things," Hamilton said. She said she has heard reports of sea lions stealing salmon from lines and nets but had not such experience herself in countless hours of fishing.

"I do see them almost ever time I go fishing," she said

Barry Espenson
Corps Study Documents Pinniped Predation at Bonneville Dam
Columbia Basin Bulletin, June 18, 2004

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