Relative Survival of Juvenile Salmon Passing Through the Spillway and the Ice and Trash Sluiceway of the Dalles Dam, 1998

摘要

High rates of spill are presumed to increase passage survival for juvenile salmonid migrants, because passage survival through spillways at Columbia and Snake River dams is generally higher than through turbines. However, there are two conditions at The Dalles Dam that may decrease spill-passage survival under high spill rates: 1) a short stilling basin combined with a shallow tailrace, which results in severe turbulence and lateral currents that may cause physical injury to migrant salmon; and 2) a large proportion of water passed through the spillway moves through shallows and islands downstream, and thus may substantially increase predation on salmonids by gulls (Larus spp.) and northern pikeminnow (Ptychocheilus oregonensis). In 1997, the National Marine Fisheries Service initiated a study at The Dalles Dam to evaluate survival of juvenile Pacific salmon (Oncorhynchus spp.) passed through the spillway when 64% of the river flow was spilled. Results of 1997 tests suggested mortality rates of about 13% for coho salmon (O. kisutch) and 8% for subyearling chinook salmon (O. tshawytscha) passing at 64% spill. In 1998, we expanded the research to include assessment of passage survival through the spillway at high spill (64% of river flow) and moderate spill (30% of river flow) and through the ice and trash sluiceway during daytime periods at moderate spill (30% of river flow). Test fish were collected from the juvenile bypass system at the Bonneville Dam Second Powerhouse, tagged with passive integrated transponder (PIT) tags, and transported to The Dalles Dam for release.