Seasonal Movement and Distribution of Fluvial Adult Bull Trout in Selected Watersheds in the Mid-Columbia River and Snake River Basins

From 1997 to 2004, we used radio telemetry to investigate movement and distribution patterns of 206 adult fluvial bull trout (mean, 449 mm FL) from watersheds representing a wide range of habitat conditions in northeastern Oregon and southwestern Washington, a region for which there was little previous information about this species. Migrations between spawning and wintering locations were longest for fish from the Imnaha River (median, 89 km) and three Grande Ronde River tributaries, the Wenaha (56 km) and Lostine (41 km) rivers and Lookingglass Creek (47 km). Shorter migrations were observed in the John Day (8 km), Walla Walla (20 km) and Umatilla river (22 km) systems, where relatively extensive human alterations of the riverscape have been reported. From November through May, fish displayed station-keeping behavior within a narrow range (basin medians, 0.5–6.2 km). Prespawning migrations began after snowmelt-driven peak discharge and coincided with declining flows. Most postspawning migrations began by late September. Migration rates of individuals ranged from 0.1 to 10.7 km/day. Adults migrated to spawning grounds in consecutive years and displayed strong fidelity to previous spawning areas and winter locations. In the Grande Ronde River basin, most fish displayed an unusual fluvial pattern: After exiting the spawning tributary and entering a main stem river, individuals moved upstream to wintering habitat, often a substantial distance (maximum, 49 km). Our work provides additional evidence of a strong migratory capacity in fluvial bull trout, but the short migrations we observed suggest adult fluvial migration may be restricted in basins with substantial anthropogenic habitat alteration. More research into bull trout ecology in large river habitats is needed to improve our understanding of how adults establish migration patterns, what factors influence adult spatial distribution in winter, and how managers can protect and enhance fluvial populations

Aquatic habitat response to climate-driven hydrologic regimes and water operations in a montane reservoir in the Pacific Northwest, USA

© 2017, Springer International Publishing. Freshwater systems are progressively becoming more stressed with increased human demands combined with expected trends in climate, which can threaten native biota and potentially destabilize the ecosystem. Numerical models allow water managers to evaluate the combined effects of climate and water management on the biogeochemical processes thereby identifying opportunities to optimize water management to protect ecosystem function, biodiversity and associated services. We used a 3D hydrodynamic model (ELCOM) coupled with an aquatic ecosystem dynamic model (CAEDYM) to compare two scenarios across three climatic and hydrologic conditions (extreme wet, extreme dry and average) for Deadwood Reservoir (USA). Additionally, we collected water temperature, water chemistry and biological data from the reservoir and inflowing tributaries to validate the model, as well as migration and growth data from Bull Trout (Salvelinus confluentus) the top predator of the food web. Modeled scenarios identified that reducing minimum outflows from 1.4 to 0.06 m 3  s -1 during the fall and winter months resulted in higher reservoir elevations and cooler water temperatures the following year, which extended reservoir rearing during the summer and fall seasons. The scenarios with reduced stream flow during the fall and winter seasons indicate benefits to the reservoir ecosystem, particularly during dry years, and could reduce the effects of climatic warming