|Document Type:||Contract Report|
|Title:||Relative survival of juvenile salmon passing through the spillway of The Dalles Dam, 1997-2000|
|Author/Editor:||R. F. Absolon, Earl M. Dawley, Benjamin P. Sandford, John W. Ferguson, Dean A. Brege|
|Publisher:||National Marine Fisheries Service|
|Contracting Agency:||U.S. Army Corps of Engineers. Portland, Oregon|
|Contract Number:||MIPR W66QKZ83437725|
High rates of spill are presumed to increase passage survival for juvenile salmonid migrants. However, at The Dalles Dam, high rates of spill may decrease spillway passage survival due to 1) a short stilling basin and shallow tailrace, which result in severe turbulence and lateral currents that may cause physical injury, and 2) a large proportion of spilled water moving through shallows and islands downstream, where rates of predation by gulls Larus spp. and northern pikeminnow Ptychocheilus oregonensi may be higher than than in the main river channel.
From 1997 to 2000, we conducted studies to evaluate the relative survival of juvenile Pacific salmon Oncorhynchus spp. through the spillway at The Dalles Dam. Study fish were tagged with passive integrated transponder tags and released into the forebay of The Dalles Dam directly in front of the spillway. Reference groups were released from a boat at the proposed site of the new bypass system outfall. Detections of study fish were collected at Bonneville Dam, from the estuary pair trawl operated in the estuary, (~rkm 74), and from piscivorous bird colonies on Rice and East Sand Island (rkm 34 and 8, respectively).
Based on data collected through four years of study, we arrived at the following conclusions: