Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 6551
Title: Relative survival of juvenile salmon passing through the spillway of The Dalles Dam, 1999
Author/Editor: Earl M. Dawley, C. J. Ebel, R. F. Absolon, Benjamin P. Sandford, John W. Ferguson
Publication Year: 2000
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: W66QKZ83437725
Pages: 123
Date: 12/01/2000

In 1999, we continued a third year of passage survival tests at The Dalles Dam, comparing 30 to 64% spill conditions.  Test fish were collected from the fish collection facility at John Day Dam and tagged with passive integrated transponder (PIT) tags.  Approximately 139,000 yearling Chinook and coho salmon were tagged in April and May (spring migrants) and 167,000 subyearling Chinook salmon were tagged in June and July (summer migrants).

About 50% of the test fish were released through the spillway at either 30 or 64% spill (~25% each), and about 50% were released in the tailrace as survival reference groups.  Half of the test fish were released at night and the other half in daylight.  The tailrace groups were released at a site away from turbulence and areas of suspected predation, and at a time to coincide with passage of treatment groups.  Spillway releases were apportioned, as equally as possible, to three lateral locations in the spillway forebay, and spill conditions were alternated every 3 d between 30 and 64% of river flow.

Based on data collected through the third year of this study, we arrived at the following conclusions:

  1.   Detection rates of fish released through the spillway at 64% spill were significantly less than for fish released downstream from The Dalles Dam.
  2.   In the two years of direct comparison between spill rates, point estimates of relative survival for fish passing at 64% spill have been lower than for fish passing at 30% spill, but these differences have not been statistically significant.  However, when annual data from 1998 and 1999 were combined for analysis, the differences were significant for spring migrants (P = 0.05) and for summer migrants (P = 0.04):  respective point estimates for passage survival at 64 and 30% spill were 92  and 98% for spring migrants and 86 and 95% for summer migrants.
  3.   Data from three years of research has indicated that spillway passage during daytime hours (adult spill patterns) produces substantially lower passage survival than spillway passage during nighttime hours (juvenile spill patterns).  Respective point estimates of survival during daytime vs. nighttime passage were 90 vs. 97% for spring migrants (P = 0.04) and 86 vs. 98% for summer migrants (P < 0.01).
  4.   Data from the 1998 evaluation of sluiceway passage indicated that for daytime passage at 30% spill, relative survival for daytime fish passage through the sluiceway was similar to that of daytime fish passage through the spillway (1 year of testing).
  5.   Evaluations of survival in relation to tailwater elevation, spill volume, river flow, and water temperature have indicated poor correlations in both spring and summer tests.

The following are recommendations for research in 2000:

  1.   Evaluate a single, constant spill rate of less than 64% with juvenile spill patterns during 24 h/d and include sluiceway and turbine passage survival.  Maximum fish numbers should be used to obtain the highest possible statistical sensitivity.
  2.   Continue evaluations that include detection data from PIT tags deposited in estuarine and lower-river bird colonies to provide increased detection numbers.
  3.   Continue assessment of differences between detection sites and evaluate combined data from 1997, 1998, 1999, and future years.
  4.   Minimize operations of the sluice chute at Bonneville Dam Second Powerhouse to maximize the PIT-tags detected at Bonneville Dam.