Evaluate Bull Trout Movements in the Tucannon and Lower Snake Rivers, 2001-2002 PDF Format - [286 KB]

SE Washington Fish Reports Evaluate Bull Trout Movements in the Tucannon and Lower Snake Rivers, 2001-02 Micheal P. Faler, United States Fish and Wildlife Service; Glen Mendel and Carl Fulton,Washington Department of Fish and Wildlife, Fish Management Division Executive Summary Introduction The recent listing of the Columbia River Distinct Population Segment of bull trout identified one of the major threats to the species as fragmentation resulting from dams on overwintering habitats of migratory subpopulations (Federal Register, 1998). It is possible that a migratory subgroup in the Tucannon River utilizes the mainstem Snake River for adult rearing on a seasonal basis (Underwood et al., 1995). The occurrence of bull trout in the hydropower system has been verified by a few incidental observations during sampling in Lower Monumental Pool (Buchanan et al. 1997 citing Ward), and in the adult passage facilities at Lower Monumental and Little Goose dams in the early 1990s (Kleist, in litt. 1993). Until recently, no attempts at adult fish enumerations were made at the Lower Monumental or Little Goose fish counting windows from Nov. 1 through March 31; bull trout are now counted year-round, with the exception of one month, usually January, when the adult ladder is de-watered for maintenance. Unfortunately, the past scheduled abandonment of fish counting activities coincides with adult bull trout movements into larger mainstem systems for adult rearing and foraging as indicated in other Columbia Basin subpopulations (Elle 1995; Faler and Bair 1992; Kelly Ringell and DeLaVergne 2000 and 2001; Schriever and Schiff, 2003; Theisfeld et al. 1996; Underwood et al. 1995). As a result, it is unknown if the existing fishways at the lower Snake River dams are suitable for bull trout passage, or if migratory fish originating from the Tucannon River attempt to pass these facilities on a regular basis. The potential for bull trout movements throughout the migratory corridor is high, but from the standpoint of future delisting and requirements set forth in the FCRPS Biological Opinion (USFWS, 2000) the determination of temporal and spatial distribution in the mainstem is crucial in developing recovery actions, estimating “take”, and successful consultation on system improvement actions. This project was designed to help meet Reasonable and Prudent Measures, and Conservation Recommendations associated with the Lower Snake River dams in the FCRPS Biological Opinion, and to increase understanding of bull trout movements within the Tucannon River drainage. Rieman and McIntyre (1993) describe unimpeded migratory corridors as important habitats to the persistence and interaction of local populations. They also indicate that disruption and/or modification of migratory corridors can increase stress, reduce growth and survival, and potentially result in the loss of migratory life- history types in a subpopulation. With these factors in mind, the primary question to be answered is: Does the existing hydropower system on the Lower Snake River limit the capabilities of Tucannon River bull trout to complete their migratory behavior, or are the current hydropower operations compatible with recovery and conservation of the species? The secondary goal of the project is to examine the movements and spatial/temporal distribution of migratory bull trout within the Tucannon River and to determine the proportion of migratory fish that leave the Tucannon River to overwinter. The bull trout stock status in the Tucannon River is considered healthy by the Washington Department of Fish and Wildlife (WDFW 1998), but little is known about their migrations in the Tucannon and Snake river subbasins. Underwood et al. (1995) conducted a radio telemetry study of adult bull trout within the Tucannon River. However, the radio telemetry was only part of a larger study so the tracking data were limited (with only a few fish tagged and only one winter of tracking) and it therefore did not provide a complete assessment of the migrations and movements of bull trout.