Proximate Composition and Energy Density of Stream-Maturing Adult Steelhead during Upstream Migration, Sexual Maturity, and Kelt Emigration

Abstract

In anadromous salmonids, muscle tissue provides the primary source of energy to support spawning migrations and spawning. We examined changes in the lipid content, protein content, and energy density of white muscle collected from stream-maturing Snake River–Columbia River steelhead Oncorhynchus mykiss during several phases of reproduction. At a basinwide scale, we estimated that between early freshwater entry and postspawning (kelt) emigration, the lipid content of white muscle was reduced by 94% to levels less than 1% of wet tissue weight. Lipid was depleted more rapidly than protein during the reproductive cycle and afterward provided the only remaining somatic energy source for the postspawning migration. We found that protein content was consistently higher in sexually mature male steelhead than in females, suggesting that energy allocation prior to reproduction varies between the sexes. In kelts, the lipid content, protein content, and energy density of white muscle were significantly higher in good-condition individuals than in poor-condition fish. Fork length was positively correlated with both protein content and energy density in kelts, suggesting that larger kelts have higher somatic energy than smaller kelts. We found no evidence of significant interannual variation in lipid, protein, and energy density of sexually mature steelhead and steelhead kelts. Postspawning survival of steelhead is likely limited by the low energy density of kelts, and our data lend support to observations of low iteroparity rates in this and other populations of inland stream-maturing steelhead.

Received August 7, 2013; accepted October 26, 2013

ACKNOWLEDGMENTS

Funding for this study was provided by the Columbia River Inter-Tribal Fish Commission through the Columbia Basin Fish Accords partnership with the Bonneville Power Administration (under Project 2007-401-00; Doug Hatch, project manager). Staff at Dworshak National Fish Hatchery provided permission and cooperation for sampling. We are grateful to the following persons for generously providing fish and assisting with collections from tribal fisheries: Bobby Begay and family; the Columbia River Zone 6 tribal fishery; and the Penney, Samuels, and Taylor families (Salmon River). The U.S. Army Corps of Engineers and the Nez Perce Tribe provided assistance with sampling of migrating kelts at Lower Granite Dam. Additional sampling and processing were provided by Boling Sun, Jessica Buelow, Kala Hamilton, Andrew Pape, William Schrader, Joe Evavold, Jon Treasure, Brad Ryan, and Bryan Jones. Carol Hoffman and Ron Hardy (Hagerman Fish Culture Experiment Station) provided assistance with analysis and interpretation of samples. We thank Tim Copeland and two anonymous reviewers for their assistance with earlier drafts of this manuscript. This study was performed under the auspices of University of Idaho Protocol Number 2009-10. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.