Washington and Oregon biologists estimate sea lions may kill as many as 10,600 sturgeon in the lower Columbia River in 2011.
“We don’t have the tools to make an accurate estimate,’’ said Cindy LeFleur, Columbia River policy coordinator for the Washington Department of Fish and Wildlife. “We know what we see happening at Bonneville Dam. We feel 10,600 is a reasonable number to put in our sturgeon population model to account for predation riverwide and across all age classes.’’
That estimate includes about 750 oversize sturgeon, the spawning portion of the population.
LeFleur first unveiled the 10,600 figure at the Washington Fish and Wildlife Commission meeting Friday in Olympia and reiterated it Monday night at a joint Washington-Oregon sturgeon meeting in Longview.
The U.S. Army Corps of Engineers has been observing marine mammal predation on spring chinook and sturgeon in the Columbia immediately downstream of Bonneville Dam since 2005.
Predation by sea lions at the dam has jumped from an estimated 413 in 2006 to 2,172 in 2010.
“Sea lion predation has been increasing (at Bonneville),’’ she said. “Both the total catch and catch per hour have been increasing basically since 2006.’’
Oregon’s draft Lower Columbia White Sturgeon Conservation Plan, more than in year in preparation, estimates marine mammal predation at 6,700 sturgeon and increasing to 10,600 next year, said Brad James, Washington’s sturgeon program manager.
Tom Rien of the Oregon Department of Fish and Wildlife said 10,600 is a high-end estimate.
Tucker Jones, also with the Oregon department, said sea lion predation on sturgeon initially was on larger fish, but as the predation grew it encompassed a broader range.
By 2010, 80 percent of the predation observed at Bonneville Dam was sturgeon 4 feet or smaller.
LeFleur said there are theories that sea lion abundance in the Columbia River Gorge is causing sturgeon to spend more time in the estuary. The handle of oversize sturgeon has increased in the estuary.
James said 99 percent of the predation on sturgeon in 2010 was by Steller sea lions, which are larger than California sea lions and are protected under the federal Endangered Species Act.
While Washington and Oregon have been able to remove some California sea lions from the area near Bonneville Dam, the Stellers were off-limits.
“With the Stellers, we have no permission to take, harm or harass in any way and remember the vast majority of the sturgeon predation we’ve observed so far is by Stellers,’’ said Bill Tweit, Columbia River policy lead for the Washington Department of Fish and Wildlife.
In late November, a federal appeals court halted the killing of California sea lions at Bonneville Dam, saying the agencies had not adequately explained how sea lions are a threat to salmon survival, but not human fishing which takes many more fish.
Tony Nigro of the Oregon Department of Fish and Wildlife said his state is working the National Marine Fisheries Service and Oregon’s congressional delegation to see about possible modifications to the Marine Mammal Protection Act to get more flexibility in dealing with sea lions.
The states also are working on petition to get Steller sea lions delisted from endangered species protection.
“Everyone is extremely aware of the risk sea lion predation poses,’’ Nigro said.