Capture Avoidance of Smallmouth Bass during Multi-pass Depletion Sampling in Virginia Rivers

When estimating population size of smallmouth bass (Micropterus dolomieu) using the multi-pass removal method with electrofishing, understanding the significance of capture avoidance is important. One-hundred-fifty smallmouth bass were tagged with external radio transmitters and monitored during depletion sampling in seven different river reaches in Virginia. Capture avoidance of radio-tagged smallmouth bass during electrofishing averaged 33.7% (SE = 5.75%). Avoidance appeared to be random across the sample reaches and there were no significant correlations between capture avoidance and fish length, season, river, or physical dimensions of the sample reaches. Emigration from the sample reaches during depletion sampling was observed. However, no pattern in upstream or downstream movement was documented. The findings from this study suggest that when using the multi-pass electrofishing technique to estimate population size, capture avoidance of the target species should be evaluated.

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