Ninety-nine percent of the Snake River sockeye counted at Bonneville Dam on the Columbia River near Portland in 2015 died before reaching Idaho’s Sawtooth Valley.
Unprecedented and lethally high temperatures in the Columbia, Snake and even Salmon rivers killed all but a few dozen of Idaho’s 4,000 adult endangered sockeye that had returned to the Columbia last June and July. Most years, more than 50 percent of the adults that survive their early life in Redfish Lake, migrate to the Pacific as juveniles and spend two years in the ocean return to spawn.
That means the 2015 return would have been the highest in more than 50 years, had temperatures been normal.
The sockeye would have gone extinct in the 1990s if not for the successful captive broodstock program created after the fish was declared endangered in 1991.
Just 2 percent of the 475,000 Okanagon River sockeye seen at Bonneville returned to their spawning grounds in Washington. Most of both populations died in the Columbia beginning in June when the water warmed to above 68 degrees, the temperature at which salmon begin to die. It got up to 73 degrees in July.
No sockeye that reached the Columbia River after July 16 completed the trip to Idaho.
The river conditions are consistent with a warming climate, Ritchie Graves, chief of the hydropower branch of the NOAA Fisheries, told the Northwest Power and Conservation Council on Wednesday. The experience could prompt his agency to reconsider how the dams should be operated to help the fish.
Sockeye had problems at the ladders of several dams. An effort by state, federal and tribal officials to collect and truck sockeye from Lower Granite Dam to the Eagle Hatchery helped save some fish, he said.
But a quicker response by fisheries and dam managers could have reduced the losses.
“We probably talked too long,” Graves told the eight-member panel appointed by the governors of the four Northwest states. “The management community probably needs to act more quickly.”
Just 56 sockeye made the trip back to the Sawtooth Valley on their own. Another 51 were trucked to the Eagle Hatchery, but 16 of those were inadvertently captured Columbia River sockeye.
Sockeye were hurt more than other salmon because they migrate in summer, after the high flows of the spring but usually before the higher temperatures of late summer. The Columbia sockeye generally migrate a little earlier than Idaho’s fish, which accounted for their slightly higher survival rate, Graves said.
The impoundments actually were cooler than the temperatures of the river flowing in, he said. Sockeye that migrated naturally from Idaho to the Pacific as juveniles survived at a higher rate than those that were captured at Lower Granite and other dams and transported downriver by barge.
“We do know the transportation program impedes homing ability,” said Russ Kiefer, a fisheries biologist with the Idaho Department of Fish and Game.
The council sets goals and makes recommendations for spending money for fish and wildlife programs from federal power revenues. Graves told the council that last year’s losses won’t set back the program if it’s just a one-time event. But if it’s repeated three of five years or six of 10, it could reverse the recovery efforts.
“We’d need to think about whether this changes the status of Snake River sockeye,” Graves said.