Bonneville Dam Now a Gated Communityby Erik Robinson, staff writer
The Columbian, February 15, 2006
BONNEVILLE DAM -- Army engineers are fortifying the gates against a remorseless invader. Last year, at least nine salmon-munching sea lions bulled their way into fish ladders funneling adult salmon through the dam and upriver to spawn. Two of them got as far as the visitor fish-viewing window on the Washington side a special annoyance to federal officials who are struggling to conserve imperiled salmon passing through the dam.
This year, the Army Corps of Engineers is spending another $1 million to keep the 800-pound animals out of the dam itself with a series of huge steel grates.
No one doubts the sea lion exclusion devices, or SLEDs, will effectively keep sea lions out of 12 fishway entrances at Bonneville Dam while allowing salmon to pass upstream in their single-minded quest to spawn. Whether it does much to reduce the bite sea lions are taking out of the total population of imperiled Columbia River salmon is another matter.
"The SLEDs will keep the sea lions out of the ladders, but they don't deal with the real problem, which is too many sea lions and not enough salmon," said Brian Gorman, spokesman for the National Marine Fisheries Service in Seattle. "The long-term solution to that something that we can all support is recovery of the salmon population."
Until then, the Corps of Engineers will do what it can to keep marauding California sea lions at bay. Early scouts have already arrived, in the form of a pair of threatened Steller sea lions spotted hunting for sturgeon in the river at the foot of the dam. Robert Stansell, a fisheries biologist for the corps, said dam workers have reported sea lions surfacing with sturgeon as large as 5 feet long.
A crane slipped the first of the steel grates into place Feb. 8.
Custom-built to slip into the dam's 12 fishway entrances, the gunmetal gray grates are designed so that they can be removed at the end of the spring salmon migration season. Openings in the 21,000-pound grates are big enough to allow salmon to slip through, but the corps will need to remove them at the end of the spring salmon migration to allow much bigger sturgeon to pass the dam.
"Our goal is to have these all in place by the first of March," said John Kranda, project manager for the corps.
A growing conflict
By that time, the initial surge of the spring salmon migration is expected to arrive with a growing contingent of hungry sea lions. Biologists say the population of California sea lions has ballooned since passage of the Marine Mammal Protection Act of 1972, and increasing numbers of the big animals have foraged all the way upriver to Bonneville in recent years in search of a meal.
Worse, corps biologists estimate the sea lions are devouring a growing portion of the salmon bound for points upriver.
"It looks like they're more efficient," Stansell said.
Even though the number of sea lions counted at Bonneville in 2005 actually dropped from 105 in 2004 to 87 last year the run of salmon arriving at the dam during the first six months of the year fell off by more than half. Observers at the dam figured the sea lions gobbled about 3.4 percent of the salmon that showed up.
While that might not sound like much, it's a big increase over the 0.4 percent of the run eaten by sea lions in 2002.
And, in the highly engineered environment of the modern Columbia River, the U.S. government makes major investments for incremental improvements in salmon survival. For example, the corps spent $55 million three years ago building a gigantic concrete chute to carry ocean-bound juvenile salmon around the dam a project expected to boost survival by 1 percent to 3 percent. "Getting a 3 percent change in survival is important," Kranda said.
Corps officials are hoping that, by keeping sea lions out of the fish ladders themselves, they can eventually discourage them from congregating in front of Bonneville Dam altogether. Federal workers plan to harass the sea lions again this year with underwater firecrackers and noisemaking guns, plus they've added another tool in their arsenal: a new underwater acoustic deterrent system devised to scatter sea lions, but beyond the hearing range of salmon.
Although the overwhelming majority of salmon returning to the river are raised in hatcheries, a portion of the sea lions' diet would include a few wild salmon returning to spawn on their own in the wild. Those are the fish protected by the Endangered Species Act.
Federal fish managers characterized the population of California sea lions and Pacific harbor seals as "healthy and robust" in a 1999 report, but the Marine Mammal Protection Act makes it difficult for resource managers to use lethal force on animals making a nuisance of themselves.
"It is a very slow and laborious process," Gorman said. "It's not a practical way to deal with nuisance animals, especially on a large scale."
Did you know?
Salmon-munching sea lions and harbor seals are nothing new to the interior Columbia River. The Lewis and Clark expedition encountered numerous sea lions more than 200 years ago 200 miles inland from the Pacific Ocean at Celilo Falls, which today is submerged beneath the reservoir created by The Dalles Dam. "Great numbers of Sea Otters in the river below the falls," William Clark wrote. "I shot one in the narrow channel today." Salmon and sea lions were both plentiful in the river.
Salmon populations, depressed by overfishing and dams, have dwindled to the point that 13 stocks in the Columbia River basin are now protected under the Endangered Species Act. California sea lions, meanwhile, have rebounded since passage of the Marine Mammal Protection Act in 1972.
learn more on topics covered in the film
see the video
read the script
learn the songs