Allocating Sampling Effort to Equalize Precision of Electrofishing Catch per Unit Effort

Abstract

Abstract.-We used a spatially explicit simulation model to examine the effects of lake shoreline length and lakewide fish density on electrofishing catch-per-unit-effort (CPUE) estimates of fish density. We also tested model predictions regarding the influence of shoreline length and fish density on precision of CPUE estimates by analyzing electrofishing data from Ohio reservoirs for juvenile gizzard shad Dorosoma cepedianum, which is a schooling fish, and largemouth bass Micropterus salmoides, a more solitary fish. Our goals were to estimate the impact of these factors on variability associated with population estimates derived from CPUE and to determine how these factors influence the minimum number of transects required to sample populations with a reliable degree of precision. Neither ''minimum transect number'' (number of transects sampled per lake in which all of 10 replicate simulations provided density estimates within Ϯ10% of the mean) nor ''minimum variance'' (variance among estimates given 20 transects/estimate) were affected by the size of lake being sampled. However, minimum transect number decreased with lakewide fish density, and minimum variance increased with fish density, particularly when fish were patchily distributed. Our results show that it is reasonable to choose one effort level (i.e., a constant number of transects per lake) for a variety of systems. This constant level of effort can achieve acceptable precision in systems differing in lake shoreline length, fish density, and fish patchiness, except in those systems having extremely low overall fish densities. In this case, more transects may be required.

Optimizing a Standardized Electrofishing Sampling Protocol for Warmwater Resident Sportfish in the Tallapoosa River, Alabama, USA

“…More samples were required to estimate CPE of Alabama bass at higher densities; whereas, the opposite was true for redbreast sunfish and redeye bass. Normally, as density increases, CV and required sample size tends to decrease (Miranda et al, 1996;Kershner and Marschall, 1998). Species-specific patterns in distribution and habitat use have been commonly documented (e.g.…”

“…The goal of these programs is to monitor population changes over time, usually in terms of abundance, size structure, body condition, or age and growth (Hardin and Connor, 1992;Vokoun et al, 2001;Zale et al, 2012). Successful standardized sampling programs obtain accurate and precise estimates of population parameters with the least amount of effort (Miranda et al, 1996;Kershner and Marschall, 1998;Brown et al, 2012). However, a wide range of factors influences capture efficiency and selectivity of electrofishing, including water conductivity, flow, temperature, and clarity (McInerny and Cross, 2000;Homan and Barwick, 2011;Reynolds and Kolz, 2012).…”

“…An often overlooked, but important, consideration for electrofishing surveys is the duration of individual samples required to maximize sampling efficiencies (Miranda et al, 1996;Kershner and Marschall, 1998;Lapointe et al, 2006). Because of habitat preferences and the fact that nearshore habitats vary spatially, fish are not evenly distributed along shorelines of aquatic systems (Irwin et al, 1997;Sammons and Bettoli, 1999;Bayley and Austen, 2002).…”