On July 15, 2010, California state and federal fisheries experts arrived at Butte Creek, expecting to capture and transport 75-80 spring run Chinook salmon which were stranded along their spawning route.
They captured and relocated 123. The salmon, which are listed as threatened under the Endangered Species Act, had stopped their migratory journey through the lower reach of the river because of rising water temperatures.
The Department of Fish and Game (DFG) and the National Oceanic and Atmospheric Administration (NOAA) combined efforts to rescue the fish. Staff netted the salmon, implanted radio transmitters in 22 of them and moved them upstream to cooler water, so they can continue their spawning migration.
“Due to the extremely low number of returning fish this year to Butte Creek, every fish is important,” said Joe Johnson, DFG Fisheries Supervisor. “We didnt expect to find 123 fish, but we were prepared. We tagged all of them and place radio transmitters in two groups of fish in two areas. We want to find out how many of these stranded salmon will survive to spawn, and what the results are for this type of rescue.”
Snorkel surveys conducted at the end of June only recorded 300 salmon in this area, instead of an expected 3,000 to 5,000. A variety of factors may have delayed or altered the normal migration timing and pattern, including a late spring and cold high flows out of the Yuba River.
The water in the Butte Creek pool where the fish were stranded is significantly warmer than the rest of the river, creating a thermal block that causes the migrating salmon to dive to the bottom in search of cooler waters. As long as the water remains warm, the fish will not move forward. This particular spot on the river has been a trouble spot for spring run salmon in previous years.
DFG fisheries staff and NOAA biologists solved the problem by setting seine nets to capture the stranded salmon. Biologists then used dip nets to capture fish out of the larger seine net and place them in a net pen.
Each fish, some of whom weighed up to 30 lbs., was carefully moved from the net pen in dip nets by a line of workers to transfer the fish up a steep bank. The fish were then loaded into a hatchery truck and transported up river for release, thus moving them around the warm water thermal block.
This year, for the second time, DFG, NOAA and staff from the University of California, Davis implanted a percentage of the rescued salmon with radio tracking devices, while the rest were tagged with small, external colored tags. The trackers will enable biologists to monitor how rescued fish behave after being rescued and if they contribute to the overall salmon population.
source: CA DFG press release