Evaluate Bull Trout Movements in the Tucannon And Lower Snake Rivers, 2005

We sampled and released 194 bull trout (Salvelinus confluentus) from the Tucannon River in 2005. Passive Integrated Transponder (PIT) tags were inserted in 105 of these individuals, and we detected existing PIT tags in an additional 67 bull trout. Twenty-one of these fish were also surgically implanted with radiotags, and we monitored their movements throughout the year. Fourteen bull trout sampled at the Tucannon Hatchery weir were not interrogated for PIT tags.

During 2005, we monitored the movements and migration of eight bull trout that were tagged in 2004, and 21 bull trout that were tagged in 2005. The general movements of these fish were typical of the movements we observed in this population from radio-telemetry work in 2002-2004. Bull trout began their upstream migration in late April through June, and continued on to the spawning areas in the upper reaches of the Tucannon River and it’s tributaries in July and August. The first post spawn outmigrant was sampled in late September, and was followed by downstream movements typical of post spawn activity throughout October. By late November and early December, radio tagged bull trout were relatively stationary, and were distributed from rm 36 at the Tucannon Hatchery downstream to rm 1.8, near the confluence of the Tucannon and Snake Rivers.

Two bull trout outmigrated into the reservoir influenced area of the lower Tucannon and Snake rivers in January. One of these fish had been tagged during 2004, and the other was tagged in the lower Tucannon River in January, 2005. Both of these fish stayed in the reservoir influenced area until March, when they began their return back to the Tucannon River. These two fish are the first documented occurrences of bull trout from the Tucannon River embarking on a seasonal migration to and from Lower Monumental Pool. As in previous years, we did not collect data associated with objectives 2, 3, or 4 of this study, because we were unable to monitor migratory movement of radio-tagged bull trout into the vicinity of the hydropower dams on the main stem Snake River.