HIGH-HEAD DAMS AFFECT DOWNSTREAM FISH PASSAGE TIMING AND SURVIVAL IN THE MIDDLE FORK WILLAMETTE RIVER

摘要: Many high-head dams in Oregon's Willamette River basin were constructed without fish passage facilities for downstream migrants. Instead, pass via hydroelectric turbines, surface spillways or deep-water regulating outlets. The availability of these routes varies seasonally with dam operations and reservoir depth, which can fluctuate by tens meters. To assess how affect movement timing survival, we used rotary screw traps below three at two riverine sites above reservoirs. Traps operated 2950 days over 8 years, >195 000 collected. Samples reservoirs primarily native salmonids (Oncorhynchus spp.), daces (Rhinichthys spp.) sculpins (Cottus while those often dominated non-native Centrarchidae. Capture rates highest from late winter to early summer, coincident juvenile Chinook salmon emigration. Conversely, collection was largely restricted fall when drawn down annual lows discharge high. We hypothesize that facilitated access turbines outlets, whereas spring–summer entrapped volitional passage. Total mortality ≤2% 36–69% dams. Estimates species salmon. Fatal injuries consistent traumas related pressure, shear contact there size-related morphology-related risk differences. Mitigation opportunities include bypass system development, retrofits existing appropriate draw allow passage. Copyright © 2012 John Wiley & Sons, Ltd.