Age and Method of Release Affect Migratory Performance of Hatchery Steelhead

Abstract

Hatchery programs that are designed to aid recovery of natural populations of anadromous salmonids, including steelhead Oncorhynchus mykiss, require locally derived, natural-origin broodstock. In such programs, achieving smoltification size thresholds may require extending hatchery rearing beyond age 1. We compared out-migration survival and travel rates of 142,990 PIT-tagged steelhead smolts released at age 1 (S1 rearing strategy) or age 2 (S2 rearing strategy) over five release years at Winthrop National Fish Hatchery (WNFH, Okanogan County, Washington). An S2 rearing cycle produced larger smolts with more uniform size distributions, resulting in higher survival during the first portion of their out-migration than for S1 smolts in three of the five release years. The S2 smolts migrated more rapidly to the ocean than S1 smolts in all years except 2011 and arrived in the Columbia River estuary 5.4 d earlier on average than the S1 smolts. The S1 steelhead that did not leave during the volitional release were subsequently forced from the hatchery to measure their survival. Nonvolitional S1 migrants were smaller and had survival rates that were 2.3–66.3 times lower than those of S1 steelhead that left WNFH on their own. The same was true for S2 steelhead, but the magnitude of the survival difference between volitional migrants and fish forced from the raceways was less variable and ranged from 2.5- to 4.6-fold. We conclude that S2 rearing can be a successful strategy for producing smolts from local natural-origin broodstock, with out-migration survival and travel times that are equivalent to or better than those of S1 smolts produced from nonlocal broodstock.

Received July 25, 2016; accepted March 31, 2017 Published online May 31, 2017

Acknowledgments

We thank the USFWS staff at WNFH and the Mid-Columbia Fish and Wildlife Conservation Office for their invaluable work in fish rearing and assistance with data collection. We also thank the staff of the National Oceanic and Atmospheric Administration–Fisheries, Northwest Fisheries Science Center, and the University of Washington for their assistance throughout the project. The Yakama Nation, Washington Department of Fish and Wildlife, and Douglas County Public Utility District assisted with broodstock collection. M. Humling created the project area map. We thank two anonymous peer reviewers for their helpful suggestions to improve the manuscript. Funding for this research was provided by the Bonneville Power Administration (Project Number 1993-056-00). Mention of trade names does not constitute endorsement by the U.S. Government.