Hyperstability in Electrofishing Catch Rates of Common Carp and Bigmouth Buffalo

Abstract

Electrofishing catch per unit effort (CPUE) can be an effective index of relative abundance when CPUE is proportional to population density. However, the relationship between fish catch rates and density can be variable and not proportional because catchability may not be constant under a range of environmental conditions. Hyperstability occurs when catch rates change faster than population density, whereas hyperdepletion occurs when catch rates change slower than population density. We used capture-mark-recapture methods to estimate density of Common Carp Cyprinus carpio and Bigmouth Buffalo Ictiobus cyprinellus across 24 lake-years. Next, we developed log-linear mixed-effects models to assess the relationship between catch rates and density to predict electrofishing CPUE based on density and environmental covariates. Common Carp and Bigmouth Buffalo electrofishing CPUE exhibited hyperstability; CPUE initially increased faster at low density but reached an asymptote as density continued to increase. Common Carp catch rates increased with water temperature and were negatively associated with season; highest catch rates occurred in the warmest temperatures of spring, whereas the lowest catch rates occurred in the coldest temperatures of fall. Bigmouth Buffalo electrofishing CPUE was negatively related to water temperature but had a quadratic relationship with season; catch rates were highest in the spring and fall when water temperatures were coldest. Secchi depth, shoreline length, and maximum depth did not influence our model predictions in either species. Electrofishing had little power to detect simulated changes in Bigmouth Buffalo density regardless of sampling effort, whereas power to detect changes in Common Carp density increase with population changes and sampling effort. At low population densities for both species, electrofishing CPUE is expected to increase or decrease faster than density and can obscure conclusions about population trajectories but may still be useful for monitoring population fluctuations if hyperstability is accounted for by a correction factor.

Intra‐Annual Variability of Common Carp and Bigmouth Buffalo Electrofishing Data in Shallow Lakes

“…Incorporating environmental covariates with CPUE data may improve the utility of CPUE as an index of abundance, especially for instances in which catch rates are not linearly related to abundance (Simonson et al. 2022). Size structures of both Carp and Buffalo were largest during fall, but the true population size structures were unknown.…”

“…Although Buffalo electrofishing can be productive under certain conditions, future efforts to sample Buffalo should consider alternative gear types to consistently and effectively sample populations and capture large numbers of fish. Incorporating environmental covariates with CPUE data may improve the utility of CPUE as an index of abundance, especially for instances in which catch rates are not linearly related to abundance (Simonson et al 2022). Size structures of both Carp and Buffalo were largest during fall, but the true population size structures were unknown.…”

“…Seasonal movements, including spawning aggregations and behavioral responses to environmental conditions such as temperature, can lead to heterogeneous temporal distributions of fish that may result in variable capture vulnerabilities as well as inconsistent size structure data (Jones and Stuart 2009;Bajer et al 2015;Herbst et al 2015). Although development of standardized sampling protocols is a basic and important component of population monitoring, little work has assessed sampling variation for Carp or Buffalo (but see Clark et al 1991;Pope and Willis 1996;Jordan 2000;Bajer and Sorensen 2012;Simonson et al 2022). Consequently, seasonal effects on catch rate, size structure, and sampling precision and effort for these species are generally unknown.…”

“…1991; Pope and Willis 1996; Jordan 2000; Bajer and Sorensen 2012; Simonson et al. 2022). Consequently, seasonal effects on catch rate, size structure, and sampling precision and effort for these species are generally unknown.…”

Precision and Bias of Three Bigmouth Buffalo Aging Structures

“…Similarly, catostomids (including Bigmouth Buffalo) in the upper Mississippi River basin comprised 35% of the total commercial harvest, resulting in an average of US$1.2 million per year between 2001and 2005(GLMRIS 2012. Commercial fishers also harvest Bigmouth Buffalo in shallow natural lakes throughout the Midwest, with harvests of nearly 400 kg Á ha À1 Á year À1 in some instances (Starostka and Applegate 1970;GLMRIS 2012;Lackmann et al 2021;Simonson et al 2022). Despite the species commercial importance, biologists have little data regarding Bigmouth Buffalo population dynamics and the potential effects of commercial harvest on populations.…”