VANCOUVER, Wash. A federal study says sea lions feeding immediately downstream of Bonneville Dam killed an estimated two percent of the upper Columbia River spring chinook salmon run in 2004.
Three years of research found sea lions had eaten more fish each year from 2002 to 2004.
Robert J. Stansell, a U.S. Army Corps of Engineers fish biologist at Bonneville Dam, said the study is not continuing in 2005.
Observers counted 31 California sea lions in 2002, but the tally jumped to 111 in 2003 and 105 in 2004. The actual count is probably 10 percent higher. The maximum count in a given day jumped from 14 sea lions in 2002 to 32 in 2003 and 37 in 2004.
An estimated 929 spring chinook and steelhead were killed between Jan. 1 and May 31 in 2002. That was 0.3 percent of the Bonneville Dam count.
But in 2003, the estimated kill by sea lions was 2,394, or 1.1 percent of the run. Last year, the kill was 3,872 fish, which computes to two percent of the run.
Three types of marine mammals harbor seals, California sea lions and stellar sea lions are found in the Columbia River. All are safeguarded under the Marine Mammal Protection Act of 1972.
Stellar sea lions are gold or silver in the water and larger than California sea lions.
Ninety-nine percent of the marine mammals at Bonneville Dam are California sea lions, said Robin Brown of the Oregon Department of Fish and Wildlife.
The population has been increasing at a rate of about 5 percent a year. In Oregon, there are 6,000 to 8,000 California sea lions, compared to counts of 2,000 to 3,000 in the mid-1980s, Brown said.
"These have caused the most grief for sport and commercial fishermen, boat owners, private and public marina operators and so on," he said. "The California sea lion is the smaller sea lion. They are brown or black in the water. They're the ones who do the barking. They tend not to be very afraid of people. They are very bold and very quick to learn new activities and new places to hang out."
California sea lions arrive at Bonneville Dam in late February and leave about mid-May. The population convenes on breeding grounds near Santa Barbara, Calif., in June and July.
California sea lions put on quite a show when they kill a salmon or steelhead, frequently tossing it in the air and attracting a swarm of gulls.
Gary Soderstrom of the Columbia River Fisheries Protective Union, a commercial fishing group, said marine mammal predation is a serious concern.
"You see 2 percent of the fish run disappearing in one small little area," Soderstrom said about Bonneville Dam. "I sport fish all up and down the river, gill net all up and down the river. I've seen certain areas like Miller Sands and Rice Island where as soon as the tide slows there's nothing but fish flying in the air, sometimes three or four at a time."
Brown said it is hard to know what percentage of the runs marine mammals kill, but it's more than two percent.
"We're not trying to imply it's not many times higher than that if you could somehow estimate the total in the river system," he said.
But to do an estimate for the entire lower Columbia River would be expensive, necessitating hundreds of boats and observers, Brown added.
Steve Watrous of the Columbia-Pacific Anglers said the 2 percent predation rate at Bonneville Dam is alarming.
"Two percent is equal to what we're allowed in the complete spring fishery," he said. "As little as two-tenths of 1 percent would free up our fishery to the point we wouldn't be fighting with the commercials or the tribes."
Brown said the sea lion population at Willamette Falls peaked in 2000, but has dropped.