Species-Specific Spatial and Temporal Distribution Patterns of Emigrating Juvenile Salmonids in the Pacific Northwest

Abstract

The vertical and horizontal distribution of juvenile salmonid migrants on approach to the dams influences bypass success in rivers. Accordingly, fish distributions have been studied for nearly three decades. These studies, however, have not been integrated and summarized in a single body of work to determine overall patterns in the spatial distribution of emigrants. We reviewed peer-reviewed and gray literature to summarize species-specific trends in the horizontal and vertical distributions of emigrating salmonids as measured by several different methods. We found that there were no species-specific differences in horizontal distributions and that fish were often oriented with the river thalweg. There were weak differences between species in vertical distributions, e.g., juvenile yearling steelhead were shallower during the day than yearling Chinook salmon. For sockeye, coho, and subyearling Chinook salmon, the data were limited or conflicting. Studies were purposefully designed to measure distributions at certain dams under particular environmental conditions for specific, local purposes. The non-standard sampling design has hampered the development of testable hypothesis on fish distributions in the Snake and Columbia rivers. Recent advances in individual-based models are offering the potential to forecast fish distributions near dams and facilitate improved bypass system design.

Keywords:

• salmon
• Columbia River
• dams
• emigration
• behavior

ACKNOWLEDGMENTS

The tests described and the resulting data presented herein, unless otherwise noted, were obtained from research conducted under the sponsorship of the U.S. Army Engineer Districts Walla Walla and Portland, the Grant County Public Utility District, and the System-Wide Water Resources Program (SWWRP), a U.S. Army Corps of Engineers research and development initiative. We gratefully acknowledge the assistance of Richard Zabel during manuscript preparation. Permission was granted by the Chief of Engineers to publish this paper.

This article is not subject to U.S. copyright law.

Notes

¹May display a multiyear freshwater residence.

¹Fyke or gill = fyke of gill net, FH = fixed hydroacoustics, MH = mobile hydroacoustics, RT = radio tag, and AT = acoustic tag.

³Relative depth calculated as peak density offish at a given depth/forebay depth or point where 75% to 80% of the fish were above specified depth.