Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 9359
Title: Survival estimates for the passage of spring migrating juvenile salmonids through Snake and Columbia River dams and reservoirs, 2017
Author/Editor: Daniel L. Widener, James R. Faulkner, Steven G. Smith, Tiffani M. Marsh, Richard W. Zabel
Publication Year: 2018
Type of Report: Draft report
Publisher: National Marine Fisheries Service
Contracting Agency: Bonneville Power Administration. Portland, Oregon
Contract Number: 40735
Project Number: 199302900

In 2017, we completed the 25th year of a study to estimate survival and travel time of juvenile Pacific salmon Oncorhynchus spp. passing dams and reservoirs on the Snake and Columbia Rivers.  All estimates were derived from detections of fish tagged with passive integrated transponder (PIT) tags.

We tagged and released a total of 21,470 hatchery steelhead O. mykiss, 19,003 wild steelhead, and 14,247 wild yearling Chinook salmon O. tshawytscha at Lower Granite Dam on the Snake River.  In addition to detections of these fish, we used detections of yearling Chinook and steelhead tagged by other researchers upstream from Lower Granite Dam and at other hatcheries and traps on the Snake and Columbia Rivers.

For groups of combined wild and hatchery Snake River fish, estimated survival from Lower Granite to Bonneville Dam was 0.478 (95% CI 0.249-0.707) for yearling Chinook and 0.459 (0.400-0.518) for steelhead.

For yearling Chinook salmon, estimated survival to McNary Dam ranged from 0.735 (0.062) for Chelan Hatchery fish released to the Chelan River to 0.248 (0.016) for Cle Elum Hatchery fish released to Jack Creek Pond.  For Upper Columbia River steelhead, estimated survival to McNary Dam ranged from 0.575 (0.108) for Wells Hatchery fish released from Similkameen Pond on the Similkameen River to 0.209 (0.056) for East Bank Hatchery fish released to the Wenatchee River.

For smolts that arrived at Lower Granite Dam, we estimated that 19.7% of yearling Chinook (wild and hatchery combined) and 22.1% of steelhead were transported from a Snake River collector dam.  These estimates were among the lowest on record (1993-2017); only estimates in 2015 were lower.

In recent years, high levels of spill have been used to boost juvenile salmonid survival through the hydropower system.  Starting in 2018, planned spill levels will increase again, to the maximum levels allowed under the gas cap.  This additional spill will further reduce the proportion of fish passing dams via the bypass systems, which will result in lower detection probabilities.

Lower detection probabilities greatly reduce the precision with which we can estimate survival using PIT-tag data.  We believe the need is now more urgent than ever before to develop PIT-tag detection capability through passage routes other than the juvenile bypass systems.  Specifically, the region should continue to place high priority on development and installation of PIT-monitoring systems for normal spill bays as well as for surface-passage structures.

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.
Characterize the population biology of species, and develop and improve methods for predicting the status of populations.