Dual-gear approach for calibrating electric fishing capture efficiency and abundance estimates

Abstract  Electric fishing depletion systematically underestimates fish abundance in streams. Electric fishing mark-recapture estimates are unbiased, but only when performed over several days to allow marked fish to recover from electric fishing. A mark-recapture procedure that can be performed in 1 day and produces unbiased population estimates is described. It involves minnow trapping, marking and releasing juvenile salmonids in a stop-netted reach, followed by electric fishing the reach 1 h after release of marked fish. Recapture of marked fish during electric fishing can form the basis of a dual-gear mark-recapture population estimate, or an unbiased estimate of electric fishing capture efficiency. The marking technique did not affect short-term catchability of the target species ( P  =   0.823), and provided unbiased estimates of capture efficiency (0.38–0.40) that were similar to those documented by other researchers. However, local validation to confirm equal catchability of marked and unmarked fish, as described in this study, is recommended.