Evaluating relative reproductive success of natural- and hatchery-origin Snake River fall Chinook spawners upstream of Lower Granite Dam

Background

Wild Snake River fall Chinook salmon were listed for protection under the Endangered Species Act in 1992 by the National Marine Fisheries Service.  Wild fall Chinook spawn upstream of Lower Granite Dam in the Snake River and the lower portions of its tributaries including the Imnaha, Salmon, Grande Ronde, and Clearwater rivers.  A genetic profile constructed by sampling wild fall Chinook salmon subyearlings in the Snake River during 1991-1995 showed distinctive patterns in allelic diversity and differentiation from Columbia River fall Chinook salmon as well as similarity with fall Chinook salmon produced at Lyons Ferry Hatchery (LFH).  LFH was selected by NMFS staff in the 1999 Biological Opinion on Artificial Propagation in the Columbia River Basin as the source for juveniles to be released upstream of Lower Granite Dam to supplement production in the wild.  

Fall Chinook salmon juveniles of LFH origin have been released upstream of Lower Granite Dam into the Snake and Clearwater rivers since 1996 and 1997, respectively.  Trends in redd counts during 1993-2003 showed a marked increase in fall Chinook salmon spawning during 1998-1993 that corresponded to the return of F1 generation hatchery adults.  Although the release of LFH fish for supplementation likely contributed to this increase, information does not exist to confirm this speculation or to determine if the F1 generation hatchery spawners are producing viable F2 generation "natural" spawners.  Determining reproductive success of natural spawners was identified as a priority by NMFS staff in the 2000 Biological Opinion for operation of the Columbia River hydrosystem.

A time-series of genetic data for Snake River fall Chinook is required to monitoring for changes in genetic profile.  One method for collecting this time-series data is to trap spawners at Lower Granite Dam and collect genetic samples.  For this strategy to be most effective, it is necessary for the sampled fish to pass upstream and spawn.  In 2004, however, fishery managers agreed that wild fall Chinook salmon should trapped at Lower Granite Dam and used in LFH broodstocks to reduce genetic divergence from the wild spawning population.  A second method is to recover adult fall Chinook salmon at spawning sites post-spawning.  We used this method in 2005 with limited success.  A total of 71 carcasses were recovered.  Scale pattern analyses showed that 14 (approximately 20%) of these were wild.  Based on a minimum desired sample size of 100 wild adults, a total of approximately 500 adults will need to be collected in 2006.

Coordination

The Washington Department of Fish and Wildlife (WDFW) in cooperation with the U. S. Fish and Wildlife Service (USFWS) is conducting this research project.  This Statement of Work is for the USFWS component of the study.  All WDFW activities, tasks and budget for the study are not included here, but can be found in their SOW under contract 25812.

Goal

The goal of our study is to determine if LFH fall Chinook salmon released for supplementation are contributing to recovery of the Snake River population.  If this is the case, we expect the genetic profile of wild-origin fall Chinook in future years to become very similar to that of LFH broodstock.

Objectives

The objective of the work described in this statement is to collect adult fall Chinook salmon for scale pattern and genetic analysis conducted by staff of WDFW.