California sea lion numbers have increased recently in the waters below Bonneville Dam but their average daily attendance this year remains the lowest it’s been since 2003, according to the April 29 status report from U.S. Army Corps of Engineers researchers at the dam.
Sea lions have been gulping around 2.4 percent of the salmon reaching the dam. The expanded estimate is that sea lions have taken 1,984 salmonids to-date, and another 77,430 spring chinook, 3,939 steelhead and three sockeye have been counted this year through Wednesday passing over Bonneville’s fish ladders.
The “expanded” take estimate has been as high as 4.2 percent (2007). Take observed in waters immediately below the dam by researchers are expanded to include estimated take during unobserved hours.
The research has been ongoing since 2002. The study was started at the urging of NOAA Fisheries, which wanted an evaluation of sea lion predation at the dam. The fish include salmon and steelhead stocks that are protected under the Endangered Species Act.
“This will drop dramatically as the thousands per day keep passing and predation drops off from about 100 per day to nothing by the end of the month,” the Corps’ Robert Stansell said percentage of take. Stansell heads the research team.
The spring chinook salmon run got off to a late start but has blossomed over the past 10 days with daily counts from Bonneville’s fish ladders ranging from 4,690 to 15,760 adult fish. Thursday’s count was 7,515.
In the past the sea lions have not tended to pick up their eating pace when the peak of the salmon run arrives, Stansell said.
The California sea lions are likely exclusively male. They forage north following their breeding season and have over the past 10 years found their way upstream to Bonneville in greater numbers than they had historically. They exit the Columbia system by the end of May to return to their breeding grounds off the coast of southern California and in northern Mexico. Steller sea lions that also visit the dam in late winter and spring are also mostly gone by the end of May.
The researchers through April 27 had seen as many as 31 Steller sea lions and 19 California sea lions at the dam on any one day. They had identified at least 70 different Stellers at the dam this year with at least 26 of those having been seen in past years as well.
At least 44 different California sea lions had been seen through April 27 compared to only 28 two weeks earlier. This year’s count includes 28 that have visited in years past.
One of the California sea lions has been observed eating at least 67 salmon through last week. The same animal took at last 198 salmon below the dam last year.
Worried about the effect of predation on salmon, the states Washington, Oregon and Idaho sought, and in March 2008 received, federal authorization to trap and kill California sea lions that feed on salmon below the lower Columbia River’s Bonneville Dam. That authority was granted by NOAA Fisheries Service.
The decision under Section 120 of the Marine Mammal Protection Act was upheld in U.S. District Court but the U.S. Court of Appeals for the Ninth Circuit panel in a Nov. 23 order remanded the issue to the lower court “with instructions to vacate the decision of NMFS and remand to NMFS.”
The NOAA decision was challenged in district court by the Humane Society of the United States, which also filed the appeal.
The Ninth Circuit decision halted the removal program. A total of 40 California sea lions were removed during the three years the program was in place. Most of the animals were euthanized but some were placed in zoos or aquariums.
The fisheries agency announced in January that it believes the Ninth Circuit decision gives it sufficient flexibility to potentially fix what the court described as “flaws” in the 2008 authorization. The agency also said resolving the conflict between a robust population of California sea lions and ESA-listed salmon and steelhead is a high priority.
NOAA Fisheries has since been analyzing its options. An announcement is expected soon.