Modified fish ladders appear to be working, study finds
BEVERLY, Wash. — Efforts to drive fish around the Priest Rapids and Wanapum dams on the Columbia River have been suspended after a study found dam modifications for migrating adult salmon were working.
The Grant County Public Utility District started trapping and hauling fish in April, as the first of 20,000 spring chinook salmon arrived in the Vantage area.
Officials were concerned the drawdown behind the cracked Wanapum dam would prevent adult salmon from using fish ladders to complete their upstream journey to spawn.
The Daily Record of Ellensburg reports that water levels behind the dam were lowered 26 feet in response to the 2-inch wide, 65-foot-long crack discovered in Wanapum Dam in February. Once the water level was lowered, the crack stabilized.
The investigation into the cause of the crack is ongoing.
But since the modifications are working, fish hauling operations were suspended.
“We expect that we will be prepared to do it (trap and haul), but we are going to monitor the fish as they come up,” Grant County PUD fisheries scientist Russell Langshaw said on Friday. “If we see issues then we can remobilize to start trap and haul again.”
Officials for Grant County decided to separate and tag 250 hatchery-reared spring chinook to observe them as they traveled from the Priest Rapids reservoir above Priest Rapids Dam through the Wanapum Dam fish ladders and Rock Island Dam.
The study was done to determine the effectiveness of the Wanapum Dam’s fish ladder modifications.
Fifty adult fish were tagged with acoustic tags, which are small sound-emitting devices that allow remote tracking of fish.
“We set up the acoustic tags in the adults and put all these different microphones throughout the project area. That way we were able to track them,” Langshaw said.
Another 200 fish were tagged with passive integrator transponder tags, which are powered by energy from an antenna nearby. The antennas, which have energy fields around them, energize the tags and send codes back so scientists can follow the fish.
After the reservoir was lowered, the Grant County Public Utility District modified the existing fish ladders on the left and right side of the Wanapum Dam to help adult fish safely pass the dam.
Modifications included installing pumps at the two fish ladders and weirs and flumes to help the migrating fish navigate to the top of the ladder and to the reservoir behind the dam.
The PUD has a staff member keeping track of how many fish go over the flume each day. There are also video cameras filming the flume all day.
Chelan County’s Rock Island Dam, about 38 miles upstream from the Wanapum Dam, also had to make modifications to ensure fish would be able to travel safely.
Meanwhile, drilling operations at Wanapum Dam are still underway to determine the exact geometry of the fracture.
Grant County PUD expects to have the cause of the fracture determined this week, and then can plan for repairs.
“Next week we’re hoping to have the cause of all of this identified,” Grant County PUD spokesman Tom Stredwick said Friday.
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