A newly completed $51 million wall constructed in the Columbia River below The Dalles Dam significantly boosted survival of juvenile salmon and steelhead migrating downstream past the dam this year, according to research presented Tuesday at a major gathering of fish scientists in Portland.
Studies showed that 96 percent of yearling chinook salmon passed the dam safely this year, up by 4 percent over similar tests in 2004 and 2005. The studies also found that 94 percent of sub-yearling chinook passed downstream safely, up by 7 percent. Also, 95 percent of steelhead survived past the dam, although past steelhead survival is not available for comparison.
The data was presented Tuesday at the U.S. Army Corps of Engineers’ Anadromous Fish Evaluation Program Annual Review conference in Portland.
Fish biologists with the Corps’ Portland District, which operates The Dalles Dam, credit the construction of the wall between spillway bays eight and nine for much of the increase in survival. The wall is 10 feet wide and 850 feet long and helps guide young fish passing through the dam’s spillways into the safest part of the river and away from predators.
“The Dalles Dam once had some of the lowest survival numbers on the river and the spillwall has transformed those into some of the highest,” said Mike Langeslay, Portland District’s Columbia River Fish Mitigation program manager. “When about 9 of every 10 fish were already making it past the dam safely, boosting those numbers by another 4 percent or 7 percent represents a major improvement.”
The salmon survival rates with the spillwall in place exceed targets established in the National Marine Fisheries Service’s 2008 biological opinion on the operation of the Federal Columbia River Power System. Those “performance standards” are 96 percent survival at each dam for both yearling chinook salmon and steelhead smolts, which head for the ocean mostly in springtime and 93 percent for sub-yearling fall chinook salmon, which migrate in late spring and summer.
ESA BiOps judge whether federal actions, such as the operation of the FCRPS dams, jeopardize the survival of listed stocks and can prescribe measures such as the construction of the spillwall to improve survival.
About 80 percent of the juvenile fish that reach the dam pass over The Dalles’ spillway. The new wall directs the flow of water from below the spillway to the deepest part of the river’s channel. That whisks the young fish away from low flow and shallow, backwater areas where they are at greater risk of predation from other fish and birds.
The project was funded through the Corps’ CRFM program, which is supported by annual congressional appropriations. The Bonneville Power Administration repays the U.S. Treasury over time for the cost of the CRFM. BPA, which markets power generated in the system, pays fish mitigation costs with ratepayer revenues.
“The Dalles spillway wall is the latest example of how the improvements we’re making in the hydro system are helping ensure that more young fish reach the ocean safely and meeting the terms of the 2008 biological opinion,” said Langeslay.
“Although we have not yet fully achieved our goals, we’ve achieved the largest increase in survival of any of the hydro system improvements outlined in the BiOp, and expect even better results in the future as we add additional predation deterrents,” he added. Planned this winter is the installation of a wire array below the dam that is intended to discourage avian predation.
The study was conducted by the Pacific Northwest National Laboratory and the University of Washington for Corps. The PNNL and UW project managers are Thomas J. Carlson and John R. Skalski, respectively. The Corps’ technical lead is Brad Eppard.
The release-recapture design used for the study to estimate dam passage survival at The Dalles Dam consisted of a combination of a “virtual” release of fish outfitted with acoustic tags at the face of the dam and a paired release below the dam. The virtual effort involved releasing tagged fish above the next project upstream -- John Day Dam “so they can get back to migrating naturally” after having been captured and handled, Eppard said. Radio telemetry was then used to identify fish that arrived alive at the face of The Dalles Dam, again in the tailrace immediately below the dam and again about two kilometers downstream.
Abstracts of the 2010 Lower Columbia River Survival Studies and other presentations at the 2010 Anadromous Fish Evaluation Program Annual Review are available on Portland District’s website at http://www.nwp.usace.army.mil/environment. For more information about the Corps’ Columbia River Fish Mitigation program, visit the Northwestern Division website at http://www.nwd.usace.army.mil/ps.
The Corps is a member of the Federal Caucus, a group of ten federal agencies that work together to protect and recover ESA-listed fish in the Columbia River Basin. Visit http://www.salmonrecovery.gov for more information.