Long Term Fish Population Monitoring, Ward Creek, Plumas County, California

Resident rainbow trout populations were monitored annually between 1989 and 2009 in Ward Creek, a small, high-gradient stream in Plumas County, California. Monitoring was conducted to evaluate potential impacts from operation of a small (1.0 MW) run-of-river hydroelectric project that can divert a maximum of 10 cfs from about 1.9 miles of stream between the intake and powerhouse.  Permanent paired replicate test and control reaches were established upstream and downstream of the intake and the powerhouse, isolated with block nets and sampled using a backpack electrofisher and standard three-pass removal-depletion method.  Patterns in trout abundance and year-class distribution were relatively consistent across all test and control reaches regardless of project operation. Cohort analyses identified a strong relationship between fry abundance and yearling trout numbers the subsequent year, and only high spring flows in abnormally wet years appeared to affect annual fry abundance.  No other biological (e.g., spawner abundance, condition factor) or environmental (e.g., low summer flow, low winter flow, winter air temperature) variables could be identified that consistently explained population trends over time.