Boat electrofishing is a common fisheries survey method is often used to obtain an index of abundance known as catch-per-unit-effort (CPUE). However, the “effort” part of CPUE is poorly defined. Early sampling guidelines suggested recording effort in both time (e.g. seconds fished) and space (shoreline distance), checking both measures for bias, and then using the least-biased metric (Reynolds 1983). Later works have gone so far as to say that time-based measures are inherently biased due to the potential for gear saturation (Bayley and Austen 2002). Despite these cautions, time-based measures of effort remain widely used.
To study the potential for bias due to effort metric we conducted surveys where three separate definitions of “effort” were measured simultaneously. For each survey we recorded time fished, shoreline distance fished, and an innovative “area fished” measure derived from a custom-built GPS tracker. Our results indicated that the time-based measurement had to potential to be biased at high catch densities whereas both spatial metrics were uninfluenced by gear saturation. More information can be found in the published manuscript.
Reynolds, J. 1983. Electrofishing. Pages 147–163 Fisheries Techniques.
Bayley, P. B., and D. J. Austen. 2002. Capture efficiency of a boat electrofisher. Transactions of the American Fisheries Society 131(3):435–451.