Relative survival of juvenile salmon passing through the spillway of The Dalles Dam, 1997

In 1997, the National Marine Fisheries Service initiated a study at The Dalles Dam to evaluate survival ofjuvenile Pacific salmon (Oncorhynchus spp.) when 64% ofthe river flow was passed through the spillway. The high spill is presumed to provide increased protection for the migrants. Research has generally found that survival offish passed through spillways at dams on the Columbia and Snake Rivers is higher than for fish passed through turbines. However, at The Dalles Dam, two conditions associated with the spillway under high spill levels are unlike other dams: 1) the stilling basin is shorter and the tailrace is shallower, resulting in severe turbulence that may cause physical injury to migrant salmon; and 2) the large proportion ofwater that passes through the shallow area may substantially increase predation on salmonids by gulls, {Lams spp.) and northern squawfish (Ptychocheilus oregonensis). Contract no. MIPR E96970020