Effects of Repeated Electroshocking on Instantaneous Growth of Trout

Abstract

Instantaneous growth rates were calculated for age‐1, −2, and −3 + wild rainbow trout (Salmo gairdneri) and brown trout (Salmo trutta) at each of eight stream sites on five streams in western North Carolina and eastern Tennessee. Growth rates of individual trout that had been electroshocked with pulsed DC two to seven times within a 12‐month period were lower than the average growth rates for trout of the same age and species at their respective sites. This decrease in growth rate occurred significantly more often among age‐1 and −2 trout than among those 3 years and older, and more often among trout that had been electroshocked within the last 2.5 months than among trout that had 3 or more months to recover from electroshocking. These results indicated that fisheries management studies should be designed to avoid repeated electroshocking, especially at intervals of less than 3 months. Growth studies in which more than a small fraction (e.g., >20%) of the total population is repeatedly electroshocked at short (<3‐month) intervals are likely to underestimate growth rates.

Evaluation of Fish Movements, Migration Patterns and Populations Abundance with Streamwidth PIT Tag Interrogation Systems, Final Report 2002.

“…However, this type of recapture produced valuable information on an individual fish without physically capturing the fish. This allowed the researcher to avoid the many possible negative impacts of electrofishing and particularly the higher probability of mortality and injury associated with repeated electrofishing (Gatz et al 1986;Mesa and Schreck 1989). Backpack efficiencies were within previously identified levels for other portable PIT tag detection units, 25 -84% (TI systems, Morhardt et al 2000;Roussel et al 2000;Zydlewski et al 2001).…”

“…This method affords the advantage of not physically harming the fish from repeated electrofishing (Gatz et al 1986;Mesa and Schreck 1989). In this study a portable unit was designed to boost recaptures and gain information on individuals that did not migrate in the Spring (when they were expected to migrate).…”

Electrofishing — Theory and practice with special emphasis on salmonids

“…The distance between collection stations should never exceed ten kilometers. Repeated electrofishing at short intervals should be avoided because frequent electroshocking (< 3 months) are likely to underestimate growth rates (Gatz et al, 1986).…”

Yakima River Species Interactions Studies, Progress Report, 1995-1997.

“…For example, large, long-lived rainbow trout living within an index reach that is sampled annually have an increasing probability of being injured by electrofishing as their size increases and the number of years they are exposed to electrofishing increases. In situations where the injury rate of these older and larger individuals is high, annual mortality is low, and the fraction of habitat sampled is large, it may be advisable to limit sampling to every other year to decrease the potential for electrofishing injuries to affect response data (e.g., growth) for research or management (Gatz et al 1986;Thompson et al 1997).…”