Improved Management of Columbia Basin Steelhead Through PIT Tagging Adult Steelhead At Bonneville Dam

Since 2009, we have PIT tagged approximately 2000 returning adult Columbia Basin steelhead annually at the Bonneville Dam and tracked these fish on their upstream migration through fish ladders and weirs.  The data has provided insights on issues of interest to Columbia Basin managers who primarily manage based for the relatively rare larger (>78 cm fork length) steelhead, designated as B-run.  We have found that B-run steelhead pass primarily in August and September and, as expected, are bound primarily for the Snake River.  However, the use of a 78 cm threshold is unlikely accurate.  Managers also manage based on counts of steelhead at adult fish ladders, however we have estimated that at some dams over 10% of steelhead ascend the fish ladders more than once thus overestimating fish counts.  Furthermore many steelhead wander widely through the Columbia Basin prior to spawning further inflating fish counts.  Approximately 5% of steelhead tracked exhibit behavior that suggests they spawned and then headed downstream to the ocean, presumably in an effort to return to the ocean.  Of these downstream migrating fish, fewer than 5% have thus far been detected returning to the Columbia Basin in subsequent years.