More Sea Lions at Bonneville Dam Enjoying Salmon Cuisineby Barry Espenson
Columbia Basin Bulletin - May 16, 2003
Apparently the fare at the foot of the Columbia River's Bonneville Dam was so fine last spring that wandering California sea lions invited along a few friends this year to sample a Northwest favorite, upriver spring chinook salmon
Historical references about sea lions and seals venturing into the Columbia River date at least as far back as the Lewis and Clark expedition. But never in recent memory have their numbers reached the level seen over the past two months.
Researchers believe that that nearly 100 individual sea lions have swum the more than 140 miles upriver from the Pacific Ocean to the dam.
Their primary mission? Taking down and eating the adult salmon, and steelhead, that are staging near the dam's powerhouses and spillways before climbing fish ladders and continuing migrations to hatcheries and spawning grounds.
Among those fishes are salmon and steelhead listed under the Endangered Species Act.
Observations of one or two sea lions have been reported in the Bonneville tailrace in almost every year since the 1980s, according to Corps of Engineers researchers who are evaluating "pinniped" predation at the dam. The National Marine Fisheries Service's 2000 biological opinion on hydrosystem operations called for research to determine the marine mammals have on listed stocks at Bonneville, in the Columbia estuary and elsewhere. The BiOp says that planned Columbia/Snake river federal hydro operations would jeopardize the existence of eight of the 12 listed stocks and prescribes measures that the agency felt necessary to avoid jeopardy.
"We've identified roughly three times as many individuals as last year," said Robert Stansell, who's leading the Corps of Engineer study. In the initial year of the study, 2002, the researchers estimated that at least 29 individual sea lions, and as many as 36, were identified in the Bonneville tailrace over the study period. As many as 11 lions were spotted below the tailrace on any one day. This year that total climbed to as many as 15.
The study entails visual observation of the area below the dam, some 733 hours worth last year during the period from mid-March to mid-May. It was estimated that the pinnepeds consumed 1,368 salmonids during the study period or about 0.54 percent of the upriver run passing in that time frame.
The vast majority of the kills were upriver spring chinook salmon. That run has experienced a bit of a revival in recent years after bottoming out in 1994 and 1995 with totals of only 21,100 and 10,200, respectively. The tally had climbed to 178,600 adults in 2000. Then the upriver spring chinook return to the mouth of the Columbia hit a record high (since counts began in 1938) at 416,500 fish in 2001, followed by the second-highest total, 295,100 last year.
The run estimate for this year is 193,000, with 168,000 adult fish having passed Bonneville through Wednesday. The spring chinook count continues through May 31, after which passing salmon are counted as "summer" chinook.
With a smaller run size, and many more sea lions milling around in the tailrace, the impact on the upriver run could climb to as high as 1 ½ percent, Stansell said.
"That may raise a few eyebrows," he said of the 2002 impacts. A clearer picture of those impacts will emerge after researchers have had time to compile and analyze the data collected during the study period. He said a summary report would be produced later this summer with a final analysis due after the New Year.
Stansell insisted that "two years does not make a trend." It is not known exactly why the sea lions have suddenly flocked to the base of the dam. This year's count included three to five harbor seals and, for the first time, a stellar sea lion.
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. The sea lions at Bonneville seem to be shifting modes now, getting ready for the journey south for the June-July breeding season.
"They're acting different, they're not feeding as aggressively," Stansell said Wednesday.
Longtime pinniped researcher Robin Brown said he was surprised, and a bit skeptical, by the estimated count at Bonneville. The Oregon Department of Fish and Wildlife biologist said those estimates will be fine-tuned after the field season ends and researchers take a closer look at the data.
Still, he said, "We know there are hundreds in the lower river. So it's not that far of a stretch," Brown said. California sea lion populations have generally been on the rebound all along the West Coast.
The animals and other pinnipeds had been considered, essentially, "vermin" by commercial fishers and others who historically would often shoot the animals on sight.
"The do eat fish and were perceived as competition for fish that humans wanted to catch," Brown said. That ended in large part with passage in 1972 of the federal Marine Mammal Protection Act.
"The population has responded and grown over the past 25 years," Brown said. Since that time West Coast numbers have climbed from an estimated low of 50,000 to nearly 300,000. It is believed, however, that the growth rate has slowed in recent years.
An initial draw for the sea lions is the returning smelt run, which floods lower Columbia tributaries -- primarily Washington's Cowlitz River -- in mid-winter. That leaves the animals poised to greet, and follow, the salmon that begin entering the river in numbers in February. The upriver spring chinook run normally peaks in late April.
With the data still being collected and tallied, NOAA Fisheries has not had a chance to evaluate the situation.
The pinnepeds' impacts "on the listed stocks, at least up to a couple years ago, were not significant compared to other sources of mortality," said Brent Norberg, NOAA Fisheries' marine mammal coordinator for the Northwest.
Any potential action to reduce sea lion predation in the area would have to involve measures such as transportation of the animals and the firing of water cannons, rubber bullets and other techniques. All have proven to have extremely short-term usefulness in moving the animals from a particular area.
"The federal law is very restrictive" in its protections of the pinnepeds, Brown said. Recommended changes to the Marine Mammal Protection Act forwarded by NOAA Fisheries nearly five years ago to Congress have languished. The changes would have allowed more flexibility in state management, including in some cases lethal control, to respond to particular situation.
With relatively large salmon runs dominating in recent years, the overall impact is likely small. The study is not funded for next year, Stansell said, but the plan is revive the study in a future year if a low run is expected.
"If they still take their share, it (impacts) could be 4 to 5 percent," Stansell said, in a year when the overall fish count is low. That total percentage of the run taken by the sea lions, 0.54 percent, is minor, especially when compared to the 42 to 65 percent impact on the winter steelhead run exacted by the infamous sea lions in the Ballard Locks area of the Puget Sound between 1986 and 1992.
"The general feeling is that sea lions can have a negative impact in a fairly localized area," Norberg said. That was cause for alarm in the early 1990s when sea lion numbers jumped from one or two to a half dozen or more at Willamette Falls.
"We were concerned at Willamette Falls when steelhead numbers were low," Brown said. Non-lethal means employed helped move the animals away, but only temporarily.
The sea lion with the biggest appetite last year devoured nine salmon in one 15-hour period and ate a total of 51 salmon over the 14 days in which he was observed. The animal also feasted on five lamprey. The 2002 analysis showed that the sea lions, on average, took about 15 minutes to consume a salmon and one minute to eat a lamprey.
Stansell said researchers have estimated that, on average, the sea lions need about 1 ½ to 2 salmon per day just to maintain their metabolism. They need fuel during what appear to be frequent journeys. One sea lion this year made the trip from Bonneville to Astoria in a mere 34 hours.
Stansell said the first three sea lions identified at Bonneville this year has also been identified last year before "new" animals were catalogued. Roughly half of the animals identified last year were seen at the dam again this year with the balance being new sightings.
The animals are identified in a number of ways -- through scars or other markings and by tags or brands. That is so researchers can catalogue the mammals' comings and goings, both within and between years. Researcher identify the animals through observations and videotape or photographs.
Brown's two-man marine mammal unit does much of its work under contract to NOAA Fisheries. The research involves evaluating populations along the coast and in the Columbia and the animals' diet. The ODFW researchers have over the past several years branded nearly 200 animals, including 200 in the past two years, Brown said. Animals found at Astoria, at the Columbia's mouth, are branded with a "C" and a number.
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