Short-Term Mortality and Injury of Rainbow Trout Caused by Three-Pass AC Electrofishing in a Southern Appalachian Stream

Abstract
Short-term (7-d) mortality and injury rates were determined for 227 wild rainbow trout Oncorhynchus mykiss sampled by three-pass AC electrofishing (500 V) in a low-conductivity stream typical of those in the southern Appalachian Mountains. An additional 67 rainbow trout were captured by angling and served as controls. Half the fish in each group were anesthetized, measured for total length and weight, marked with an adipose fin clip, and sampled for scales to simulate the effects of a typical handling regimen; the other half were not handled. All fish were held in a partitioned raceway adjacent to the study stream. Two fish died during sampling (1%) and five other fish died within 24 h of the completion of electrofishin g. All control fish survived. Thirteen electroshocked fish could not be accounted for after the 7-d observation period and were treated as sampling deaths. Mortality rates were 9% overall, 10% for handled fish, 7% for unhandled fish, and 12, 9, and 4% for the first, second, and third electrofishing passes, respectively. Mortality did not differ significantly between handled and unhandled fish or among electrofishing passes. Mortality rates for age-0 (< 100 mm) and adult (100-234 mm) fish (20 and 6%, respectively) were significantly different. Seventy-six fish, including all 7 of the recovered fish that died, 57 survivors (including handled and unhandled fish from all passes), and 12 controls (handled and unhandled), were X-rayed and dissected to determine the incidence of spinal injuries and hemorrhages. Two electroshocked rainbow trout (3%) had spinal injuries and two others (3%) had hemorrhages along the spinal column but no spinal injuries; no injuries were detected among the seven fish that died or the controls. Based on these results and 4 years of data from a nearby monitoring station, we conclude that rainbow trout mortality and injury rates caused by three-pass depletion sampling with AC are tolerable. This conclusion is limited, however, to relatively small, short-lived fish inhabiting low-conductivity waters that characterize southern Appalachian streams.

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