About 1 million sockeye salmon smolts were released ahead of schedule from the Sawtooth Fish Hatchery last week after a “high-intensity runoff” killed several thousand young fish.
Idaho Fish and Game reported that the hatchery’s water source, the Upper Salmon River, had increased in temperature, had low dissolved oxygen levels and high turbidity because of recent spring run-offs. The hatchery staff said 31,250 sockeye smolts, less than 3% of the total, died as a result.
The smolts were raised at the Springfield Hatchery southwest of Blackfoot and were in their final stage of acclimation at the Sawtooth Hatchery before being transported and released into Redfish Lake Creek this week.
“Rather than risking additional mortality, Fish and Game managers decided to release the remaining estimated 1,012,648 smolts slightly early and directly from the hatchery into the Upper Salmon River,” Fish and Game said in a news release. “This decision was based on fish conditions in the raceways and a forecast for continued warm weather.”
From the Stanley area fish hatchery, the smolts head down the Salmon River to the Snake River where they encounter the Lower Granite Dam.
The first time Springfield hatchery fish were released into Redfish Lake Creek in 2017, most died before reaching the first dam. Biologists determined the smolts couldn’t acclimate to the hard water in the creek after being raised in the soft water at the Springfield fish hatchery. Since that time, the fish spend time acclimating at the Sawtooth Fish Hatchery in medium-hard water.
“In a typical year is takes hatchery-reared smolts an average of approximately 10 days to reach Lower Granite Dam following release into Redfish Lake Creek,” said Roger Phillips, Fish and Game information supervisor. “A portion of the sockeye salmon smolts are transported past the dams on the Columbia River. The total fraction of the run that is transported varies from year to year.”
The sockeye will spend the next two years in the ocean before migrating back to Idaho. Some estimates say as many as 150,000 of the bright red spawning fish would annually turn the Stanley area nursery lakes red. Recent decades have seen the numbers dwindle to a handful, prompting Idaho to devote the Springfield Hatchery to producing a million smolts to release this spring.
About 660,000 hatchery-raised juvenile fish were released in 2018 and 27 fish returned in 2020. The fish were listed as endangered under the Endangered Species Act in 1991.
“Our adult return forecast for 2021 is 255 adult Snake River sockeye to the Sawtooth Valley,” Phillips said. “Most of our sockeye return after spending two years in the ocean. Therefore, we would expect to see the majority of fish released this year return in 2023.”
Fish and Game said because the smolts this year were released directly from the Sawtooth Hatchery into the Upper Salmon River instead of Redfish Lake Creek, it “will likely increase the number of adult sockeye that return to Sawtooth Hatchery in two to three years rather than migrating up Redfish Lake Creek.”
The hatchery has facilities to trap the returning adult sockeye to harvest their eggs for the next cycle, Fish and Game said.
“Even for smolts released into Redfish Lake Creek, it is common for a portion of them returning as adult sockeye to be trapped at Sawtooth Hatchery,” Fish and Game said.
Redfish Lake Creek is about 2 miles from the Sawtooth Hatchery.