Biologists say the sea lions that scoop up fish at the foot of Bonneville Dam on the Columbia River have killed more sturgeon this year than salmon.
Two different species of sea lion like to feast at the fish at Boneville. California sea lions only eat salmon, but Steller sea lions arrive earlier in the year, and while they wait for the spring salmon run to start, they snack on sturgeon.
Biologists with the Army Corps of Engineers estimate that this year, the Steller sea lions ate about 2,500 sturgeon and 1,293 salmon and steelhead.
California sea lions, the species that began frequenting the Bonneville dam first and has been selectively removed and killed since 2008, ate an estimated 1,067 salmon and steelhead and didn't eat any sturgeon.
The estimates were released as part of a 2012 field report, and are based on more than 3,000 hours of observation of the pinnipeds.
The corps is among several federal agencies that are legally required to work on protecting the Columbia's threatened and endangered species of salmon and steelhead. The new findings have them concerned about sturgeon, which aren't under the same federal protection.
Corps spokeswoman Diana Fredlund says the sea lions mainly devoured sturgeon about 3 feet long, likely young adult fish ready to reproduce.
“They spawn multiple times in their lives so that’s one of (the) concerns," Fredlund said. "As they’re getting these larger sturgeon, they lose all of their children.”
The sea lions also consumed an estimated 79 lamprey.
Oregon and Washington have authorization to remove and kill California sea lions, and have removed 13 this year. Twelve were killed; one was transferred to a zoo. But the larger Steller sea lions are a threatened species, and fisheries managers at the dam are limited to hazing them.
The field report notes that as the number of salmon and steelhead eaten by California Sea lions at Boneville has dropped off a little, the number eaten by Steller sea lions has increased quickly, creating new complications. In 2008, Stellar sea lions were responsible for just 3.8% of the estimated predation at the dam; by 2012, they were responsible for 53.3%.
The field report, which was authored by biologists with the Army Corps of Engineers, urges the Oregon and Washington fish and wildlife agencies to strongly consider adding additional traps at Bonneville, and increasing the number of California sea lions targeted for removal from a dozen to around 30.
The National Marine Fisheries Services has issued a permit to Oregon and Washington, authorizing the removal and killing of up to 90 California sea lions a year at Bonneville for a period of five years. The permit only applies to sea lions that have been observed at the dam for at least five days.
The Humane Society of the United States has challenged the permit in court, arguing that commercial and recreational fishing have a much more significant impact on salmonid population numbers. Oral arguments in the case are scheduled Friday in U.S. District court in Portland, and a judge has limited the number of California sea lions that can be killed at 30, while the case progresses.