Estimation and Modeling of Electrofishing Capture Efficiency for Fishes in Wadeable Warmwater Streams

Abstract

Stream fish managers often use fish sample data to inform management decisions affecting fish populations. Fish sample data, however, can be biased by the same factors affecting fish populations. To minimize the effect of sample biases on decision making, biologists need information on the effectiveness of fish sampling methods. We evaluated single-pass backpack electrofishing and seining combined with electrofishing by following a dual-gear, mark-recapture approach in 61 blocknetted sample units within first-to third-order streams. We also estimated fish movement out of unblocked units during sampling. Capture efficiency and fish abundances were modeled for 50 fish species by use of conditional multinomial capturerecapture models. The best-approximating models indicated that capture efficiencies were generally low and differed among species groups based on family or genus. Efficiencies of single-pass electrofishing and seining combined with electrofishing were greatest for Catostomidae and lowest for Ictaluridae. Fish body length and stream habitat characteristics (mean cross-sectional area, wood density, mean current velocity, and turbidity) also were related to capture efficiency of both methods, but the effects differed among species groups. We estimated that, on average, 23% of fish left the unblocked sample units, but net movement varied among species. Our results suggest that (1) common warmwater stream fish sampling methods have low capture efficiency and (2) failure to adjust for incomplete capture may bias estimates of fish abundance. We suggest that managers minimize bias from incomplete capture by adjusting data for site-and species-specific capture efficiency and by choosing sampling gear that provide estimates with minimal bias and variance. Furthermore, if block nets are not used, we recommend that managers adjust the data based on unconditional capture efficiency.

Factors influencing riverine fish assemblages in Massachusetts

“…Fish samples were limited to those collected by use of backpack and barge electrofishing gear (pulsed direct current) during a single upstream pass. Single-pass backpack electrofishing has been determined to be an effective and reliable approach for obtaining information on fish-assemblage structure, such as species richness, when based on consistent sampling protocols (Angermeier and Smogler, 1995;Bertrand and others, 2006;Price and Peterson, 2010; but see Meador and others, 2003). Fish-sampling data were screened for electrofishing sampling efficiency to improve sample consistency and to exclude sites where sampling conditions precluded capture of a representative cross section of the fish assemblage.…”

Long-Term Monitoring Data Provide Evidence of Declining Species Richness in a River Valued for Biodiversity Conservation

“…Survey data for stream fishes typically comprise lists of species encountered at particular times and places, often with counts of individuals. However, count data typically lack explicit measures of capture efficiency, which may vary depending on habitat conditions during sampling and thus confound comparisons among counts made at different times (Yoccoz et al 2001;Price and Peterson 2010). In this study, we have used changes in observed species occurrences, rather than count data, to evaluate evidence of temporal faunal change.…”

Estimating juvenile Chinook salmon (<i>Oncorhynchus tshawytscha</i>) abundance from beach seine data collected in the Sacramento–San Joaquin Delta and San Francisco Bay, California

“…Heterogeneity in capture can vary among beach seine sampling methods, environmental conditions, and fish species and sizes (Murphy and Willis, 1996). Furthermore, failure to account for this sampling bias can introduce systematic error into the data, obfuscate important ecological relations, and negatively influence a manager's ability to make effective resource management decisions (Price and Peterson, 2010).…”

“…Gear calibration methods require comparing the number of fish captured with beach seines to the known number or an unbiased estimate of the number of fish present in the sample area (Peterson and Paukert, 2009;Price and Peterson, 2010). A primary assumption of most fish abundance estimators (for example, removal or depletion methods; Parsley and others, 1989;Pierce and others, 1990) and all gear calibration methods is that the population is geographically closed while sampling (no immigration or emigration; Peterson and Paukert, 2009).…”