|Document Type:||Contract Report|
|Title:||Relative survival of juvenile salmon passing through the spillway and the ice and trash sluiceway of The Dalles Dam, 1998|
|Author/Editor:||Earl M. Dawley, Lyle G. Gilbreath, R. F. Absolon, Benjamin P. Sandford, John W. Ferguson|
|Publisher:||National Marine Fisheries Service|
|Contracting Agency:||U.S. Army Corps of Engineers. Portland, Oregon|
|Contract Number:||E96970020, W66QKZ82167243, W66QKZ83437725|
In 1997, we 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 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. We tagged approximately 64,000 yearling coho salmon in April and May, and 80,000 subyearling Chinook salmon in June and July. Nearly equal portions (20% each) of these fish were released through the spillway at 64% spill, the spillway at 30% spill, and the sluiceway at 30% spill; about 40% were released in the tailrace as survival reference groups.
Relative survival for passage at 64% spill was 89% for coho salmon (CI 82-96%) and 75% for subyearling Chinook salmon (68-83%). These survival rates were substantially lower than survival at 30% spill, where coho survived at 97% (88-107%) and subyearling Chinook at 89% (80-99%). The difference between passage survival at 64% and passage survival at 30% was insignificant for coho and significant for subyearling Chinook. Relative survival for sluiceway passage was 96% for coho (87-105%) and 89% for subyearling Chinook (81-98%), and these rates did not differ appreciably from those of spillway passage at 30% spill. Spillway passage survival of coho and subyearling Chinook salmon appeared to decline through the period of testing.
From the 2 years of study, results that appear important to operations at The Dalles Dam are as follows:
We recommend continued testing of 30 vs. 64% spill rates during spring and summer fish migrations, followed by testing of a constant rate of spill (less than 64%) with a 24-h/d juvenile fish pattern comparing spillway vs. sluiceway releases. Additionally, recovery and evaluation of PIT tags deposited in estuarine bird rookeries should be continued so as to provide increased detection numbers, and comparisons of survival rate differences among detection sites should also be continued. To maintain sufficient detections at Bonneville Dam Second Powerhouse, we also recommend minimal use of the sluice chute.