Abstract

Depletion electrofishing is a common management tool for obtaining quantitative data on trout populations in wadeable streams. Very few studies have examined the effects of electrofishing on native, non-game fishes and in particular, those non-target species that can be subjected to multiple electrical shocks routinely used in 3-pass depletion sampling programs for salmonids. Potential effects include cardiac or respiratory failure, spinal or other related internal injuries, stress and fatigue, behavioral change and mortality. In this study we evaluated PDC electrofishing forms on several species common to Appalachian streams including brook trout (Salvelinus fontinalis), rainbow trout (Oncorhynchus mykiss), Potomac sculpin (Cottus girardi), green sunfish (Lepomis cyanellus), fathead minnow (Pimephales promelas), largemouth bass (Micropterus salmoides), and channel catfish (Ictalurus punctatus). Fish were held in four rectangular fiberglass tanks (190 cm x 66 cm) equipped with electrodes, a gravel/cobble stream substrate and continuous water flow. Three tanks served as experimental chambers and the other as a control. An anode and cathode were placed at opposite ends of the tanks and connected to a Smith Root Type LR-24 Backpack Electrofisher. Voltage gradients were measured for each electrofishing field with a Fluke Model 199C oscilloscope and the average voltage gradient (V/cm) was calculated. Fish were exposed to either one, two or three shocks spaced 1-h apart. A minimum of ten (10) fish were examined for hemorrhagic trauma and for spinal deformities, compressions and fractures. Radiographs were made with a Tech America MT8020 for 180 seconds at 20 kV. Whole blood glucose (mg/dL), serum lactate (µM), and a variety of other serum chemistry parameters were measured thirty minutes post-shock in a minimum of ten fish per treatment per species. In general, the salmonids experienced greater trauma than the non-target species under similar treatments, and these injuries were largely independent of the number of electrical shocks sustained. Injuries among non-target fish were generally categorized as minor to moderate in severity. Across all species, lactate was the most reliable predictor of physiological stress related to electrofishing. Some other clinical chemistry parameters such as whole blood glucose, aspartate aminotransferase, and creatine kinase also showed positive correlations with hemorrhagic trauma scores among some of the species examined. Among the salmonids, 30-day post treatment survival was >94%; among the other five species, 30-day post treatment survival ranged from a low of 80% among fathead minnows to 100% in green sunfish and channel catfish.