Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8240
Title: Responses of Snake River fall Chinook salmon to dam passage strategies and experiences (DRAFT)
Author/Editor: Steven G. Smith, Tiffani M. Marsh, William P. Connor
Publication Year: 2014
Publisher: National Marine Fisheries Service and U.S. Fish and Wildlife Service
Contracting Agency: U.S. Army Corps of Engineers. Walla Walla, Washington
Contract Number: MIPR W68SBV20386114
Pages: 134
Date: 12/2/2014

We completed analyses for a 6-year study (2006 and 2008-2012) to evaluate the response of juvenile migrant fall Chinook salmon Oncorhynchus tshawytscha to two different fish-passage strategies employed at transport collector dams on the Snake and Columbia Rivers. 

Data on smolt-to-adult ratios from our releases in 2006 and 2008-2012 suggest that adult returns would be maximized by a management strategy of bypassing fish from the juvenile bypass systems early in the season at Lower Granite, Little Goose, and Lower Monumental Dams and then switching to transportation later in the summer.  Based on a grand geometric mean of T:B ratios (transport-to-bypass) for the two subyearling types (weighting the two types equally) at the three dams for which we calculated model-averaged daily estimates, the best day for starting transportation would be on or near 1 July.

Data for McNary Dam were not sufficient to determine within-season patterns satisfactorily.  However, annual totals for McNary Dam showed a large advantage for transported fish.  These annual totals, combined with the consistent pattern of increasing survival for fish transported later in the season at each of the other dams, suggest that transportation from McNary Dam likely led to higher SARs for fish arriving later in the season and possibly for those arriving earlier as well.

The methods of analysis and results reported here are novel and represent extensive development of our analytical approach for over a decade, beginning with the first transportation studies of juvenile fall Chinook salmon in 2001.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.