Steelhead Abundance, Survival, and Distribution Patterns Following the Removal of Powerdale Dam (Hood River, OR)

In June 2003 tribal, utility, government, and conservation groups agreed to remove Hood River's Powerdale Dam, and during the summer of 2010 that initiative was completed.  Ineffective fish screening, de-watering of habitat downstream of the dam, and marginal upstream fish passage negatively affected indigenous fish populations.  Five years after habitat connectivity was restored to the mainstem river, positive trends in steelhead populations possibly related to dam removal may be developing.  Using mark-recapture methods we estimated that the mean annual wild steelhead smolt abundance (FL ≥ 150mm) was 14,087 for outmigration years 1994 – 2010, however since dam removal (2011 – 2015) mean smolt abundance increased to 31,081.  Logistic regression modeling indicated dam removal positively impacted wild steelhead abundance however environmental variables (i.e. flow variability, periodicity) are also significant factors.  Radiotelemetry data (Lotek MCFT2-3A tag, SRX400A receivers) collected pre- and post-dam removal indicated that adult steelhead spawning distribution has remained relatively consistent (MaxEnt v3.3.3), although temporal differences may be indicative of increased access to spawning habitat.  The fact that the lower river is no longer fragmented and steelhead smolt abundance has been trending upward since 2010 while survival during outmigration has remained relatively steady is encouraging from a recovery perspective.