Young chinook and sockeye salmon also made it safely through the eight federal dams at higher-than-average rates, NOAA’s Northwest Fisheries Science Center found.
Researchers said the higher survival rates likely reflected two factors: the spill of water to help carry young fish past dams and recently installed surface passage systems that let fish slide through spillways near the water’s surface, where they naturally migrate.
Spill and surface passage are both central components of the federal biological opinion that outlines measures to protect Columbia and Snake river fish listed under the federal Endangered Species Act. The biological opinion calls for spill at all eight federal dams on the Columbia and Snake rivers through the end of the active juvenile salmon migration in August.
The US Army Corps of Engineers has also installed surface passage systems at all eight federal dams on the Columbia and Snake rivers in the last decade. Electric ratepayers fund most of the improvements through the Bonneville Power Administration.
NOAA research indicated that the surface passage systems, such as a new temporary spillway weir – also called a fish slide – at Little Goose Dam, helped speed young fish downstream by moving surface water more quickly through spillways. Faster travel downriver increases survival by reducing the exposure of young fish to predators and higher water temperatures, NOAA’s report said.
About 35% of fish were transported downstream by barge, fewer than in almost all previous years since 1995.
NOAA’s report also indicated that new aerial wires to reduce bird predation below John Day Dam and completion of a spill wall to guide fish away from predators at The Dalles Dam aids fish survival through the final three Columbia River dams – John Day, The Dalles and Bonneville. About 95% or more yearling salmon and steelhead passed safely through each of the three dams.
