Juvenile Anadromous Salmonid Production in Upper Columbia River Side Channels with Different Levels of Hydrological Connection

Abstract

We examined the contribution of three types of side channels based on their hydrologic connectivity (seasonally disconnected, partially connected, and connected) to production of juvenile anadromous salmonids. Juvenile steelhead Oncorhynchus mykiss and Chinook Salmon O. tshawytscha were found in all three of these side channel types and in each year of the study. Upon connection with the main stem at high flows, the seasonally disconnected side channels experienced an emptying out of the previous year's fish while filling with young-of-year fish during the 2- to 4-month period of hydrologic connection. There were no differences between the densities of juvenile steelhead and Chinook Salmon and the rate of smolts produced among the three types of side channels. Recently reintroduced Coho Salmon O. kisutch had sporadic presence and abundance in partially and connected side channels, but the smolt production rate was over two times that of steelhead and Chinook Salmon in seasonally disconnected side channels. Within seasonally disconnected side channels, young-of-year salmonids in deep pools (≥100 cm) had greater survival than those in shallow pools (<100 cm). Densities of juvenile steelhead in all side channel types were similar to those in tributaries and were higher than in main-stem lateral margins. Juvenile Chinook Salmon densities were higher in side channels than in both tributary and main-stem lateral margins. Our results suggest that improving quality of pool habitat within seasonally disconnected side channels can result in improved survival for juvenile anadromous salmonids during the period of disconnection. Habitat improvement in these seasonally disconnected side channels should be recognized as a worthy restoration strategy, especially when full connectivity of side channels may not be a feasible target (e.g., through lack of water availability) or when full connectivity may present too high a risk (e.g., flooding, stream capture, bank destabilization).

Received August 30, 2013; accepted December 9, 2013

ACKNOWLEDGMENTS

Much of the field work was conducted by U.S. Geological Survey (USGS) personnel, including Wesley Tibbits, Grace Eger Watson, Teresa Fish, Nick Glaser, Kyle Koger, Keith Watson, Alison Duranleau, Emily Lang, Cara Bell, and others. Additional field assistance was supplied by Idaho State University's James Ryan Bellmore and David Ayers. Access was granted to work on the side channels from various landowners including: Jim Habermehl and Blaine Rogers. The Methow River work was supported from a larger effort funded by the U.S. Bureau of Reclamation, which was administered by Michael Newsom. We would like to thank Jennifer Molesworth of the U.S. Bureau of Reclamation, Ted Jones of the USGS, and two anonymous reviewers for reviewing this manuscript. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Government.