Shocking Results: Assessing the Rates of Fish Injury from Pulsed-DC Electrofishing

Abstract: Electrofishing is one of the more commonly used techniques for sampling fish in freshwater ecosystems. In the present study, four native fish species (Bluegill Lepomis macrochirus, Channel Catfish Ictalurus punctatus, Freshwater Drum Aplodinotus grunniens, and Gizzard Shad Dorosoma cepedianum) and two invasive species (Common Carp Cyprinus carpio and Silver Carp Hypophthalmichthys molitrix) that were captured in the Mississippi and Illinois rivers were assessed for evidence of vertebral injuries from pulsed-DC (PDC) boat electrofishing. Fish were collected by electrofishing crews conducting routine standardized sampling for two long-term monitoring programs. Fifty percent of Silver Carp and 27% of Channel Catfish were injured; no injuries were observed for the other species examined. Injury rates for Silver Carp were 71% in the Illinois River and 30% in the Mississippi River. The Silver Carp injury rate was positively correlated with conductivity, temperature, and pulse frequency and negatively correlated with TL. In contrast, the injury rate of Channel Catfish was similar between rivers and exhibited no correlation with TL, condition factor, conductivity, or temperature. Our results demonstrate that Silver Carp and Channel Catfish in the upper Mississippi River system are sustaining injuries from PDC electrofishing. The observed effects of pulse frequency on the Silver Carp injury rate suggest that managers could alter the pulse frequency settings for the electric barriers at the Chicago Sanitary and Ship Canal and for other electricity-based management efforts to reduce Silver Carp populations in the Chicago Area Waterway System.