Patterns of Migration and Delay Observed in PIT Tagged Summer Steelhead from the Upper Columbia and Snake River Basins

In recent years, large numbers of known-origin adult steelhead tagged with passive integrated transponder (PIT) tags, widely distributed PIT-tag detectors, and the PTAGIS database allow unprecedented, detailed analysis of adult summer steelhead migration behavior in the Columbia and Snake rivers. 

Columbia Basin summer steelhead begin entering the river in June-November and spawn in March-June of the following year.  Returning summer steelhead adults are generally assumed to proceed directly to their spawning location, or someplace nearby, where they remain until spawning.  Most upper Columbia Basin steelhead display this behavior.  However, many Snake River summer steelhead delay in the lower Columbia River before moving upstream.  This delay can range from a few weeks to overwintering with resumed migration in the spring to spawn.  These observations are and suggest that some Snake River steelhead are delaying upstream migration until temperatures cool in the fall. 

Observations also indicate that some steelhead are overshooting their natal streams, and then return downstream to complete their migrations.  This suggests that fish observed in unexpected locations are not always “strays” and that safe downstream passage of adult summer steelhead past hydroelectric dams throughout the Columbia basin migratory corridor may be important for the recovery of some steelhead populations.