Movement and Capture Efficiency of Radio-Tagged Salmonids Sampled by Electrofishing

Abstract

Electrofishing-based estimates of fish abundance are common. Most population models assume that samples are drawn from a closed population, but population closure is sometimes difficult to achieve. Consequently, we individually electrofished 103 radio-tagged trout of two species, westslope cutthroat trout Oncorhynchus clarkii lewisi and brook trout Salvelinus fontinalis, in five streams in western Montana to quantify the influence of habitat and fish size on capture efficiency and movement related to electrofishing with unpulsed DC. First-pass capture efficiency was 46% and declined on subsequent passes. No variables were related to capture efficiency, and only the percentage of cobble or larger substrate was related to the probability that uncaptured fish would move during the first electrofishing pass. About 20% of the uncaptured fish did not move, and 95% traveled less than 18 m. We concluded that for these streams, the bias in abundance estimates from disregarding movement would be relatively minor.

Received January 18, 2011; accepted June 11, 2012

ACKNOWLEDGMENTS

We thank Robert Clark and Tracy Elam for assistance in the field and data preparation. Funding was provided by the U.S. Bureau of Land Management (BLM) Missoula field office and Northwestern Energy (NWE). We thank Jo Christensen (BLM) and Sam Milodragovich (NWE) for logistical support.