Sockeye Vanish Mid-Streamby Greg Stahl
Idaho Mountain Express, September 8, 2004
Salmon river fisheries biologists look for answers
Sockeye salmon have returned to the Sawtooth Valley, but the numbers have biologists scratching their heads.
At least 110 adult sockeye salmon were counted earlier this summer as they passed Lower Granite Dam on the lower Snake River, the last of eight dams on the Columbia and Snake the fish must circumvent on their 900-mile trip from the Pacific Ocean to Central Idaho. But to date, only six sockeye have been trapped at Sawtooth Valley weirs operated by the Idaho Department of Fish and Game.
An additional 16 adults are holding below the Sawtooth Fish Hatchery in the Salmon River but have not yet entered the trap.
That leaves 88 fish that are unaccounted for.
“They just drop out and disappear,” said Dan Baker, Fish and Game’s Eagle Fish Hatchery manager.
Last year, three adult sockeye salmon returned to the Sawtooth Valley, but only two entered the trap.
Fisheries Research Biologist Catherine Willard said the percentage of adults passing Lower Granite Dam that reach the Sawtooth Valley is significantly lower than in previous years.
Biologists refer to this as the “conversion” of adults from one point to the next in their journey. Typically, 50 percent of sockeye salmon adults that pass Lower Granite Dam make it to the Sawtooth Valley. It was as high as 80 percent only four years ago in 2000. But over the last several years, the conversion hovered around 25 percent.
Willard said the low conversion of adults from Lower Granite Dam is a concern for the program.
“We need to examine as many sockeye salmon adults as we can this year to try to better understand what is causing the low conversion,” she said.
If the sockeye salmon holding below the weir do not swim into the trap on their own power by mid-September, Fish and Game program cooperators are planning to capture the adult sockeye salmon by seining or hooking so they can determine if something like disease might be affecting their migration.
Baker said there are a number of theories about what is happening to the fish, but no solid data. The causes of the low conversion rates could be due to disease, warmer water or predators.
“It’s just a long ways for them to come,” he said. “Maybe they’re dropping off because they get too tired.”
The fish returning to the Sawtooth Valley were produced by the Redfish captive broodstock program, which was initiated in 1991 just before Redfish Lake sockeye salmon were placed on the federal endangered species list. Captive propagation is used to protect at-risk populations.
Rearing fish in the hatchery from the egg stage to adulthood is thought to maximize survival and reproduction.
The broodstock program is a cooperative effort with Fish and Game, the Shoshone-Bannock Tribes, the University of Idaho and the National Oceanic and Atmospheric Administration-Fisheries.
It is funded by Bonneville Power Administration as partial mitigation for the federal Columbia River power system.
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