Evaluation of an Electric Fish Guidance System in the South Canal of the Gunnison River, Colorado

An electric fish guidance system (EFGS) was installed to reduce fish entrainment in the South Canal with the construction of two hydropower plants in 2012.  The objective of this study was to monitor fish entrainment and evaluate the effectiveness of the EFGS.  Three groups of fish were tagged and released upstream of the EFGS; fish from the canal, Gunnison River fish, and hatchery reared fingerlings.  Mark recapture boat electrofishing was completed and population estimates were made with the Huggins Closed Capture model using fish length to model capture probabilities.  The study reach contained 2,994±1,043 fish (>150 mm) in Oct-2011, 1,764 ±279 in Oct-2013, 1,224 ±239 in Jul-2014 and 1,900 ±379 in Oct-2014.  Fish population estimates have declined after the EFGS, but not significantly at the 95% level.  The number of fish >350 mm has increased, but not significantly.  A total of 288 tagged fish <300 mm and four fish >300 mm were recovered below the EFGS, 1.3% of all tagged fish.  The EFGS and turbine mortality appear to exclude larger fish from the study reach but that effect is offset by the growth and survival of numerous smaller entrained fish, resulting in no significant differences before and after the EFGS.