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

Abstract

AbstractCommon Carp Cyprinus carpio and Bigmouth Buffalo Ictiobus cyprinellus are widespread across the Midwest, where they can achieve high population densities in shallow lakes. Despite their contrasting statuses as invasive and native fishes, these species are commonly managed together due to their capacity to have deleterious effects on water quality. However, intra‐annual sampling variability is poorly understood for both species, making it difficult to track population changes. We compared boat electrofishing CPUE and proportional size distribution (PSD) of Common Carp and Bigmouth Buffalo during May–October 2018–2020 in seven shallow northwestern Iowa lakes. We also estimated sampling effort necessary to reach targets of fish captured (100) and precision (relative standard error < 25%) and to detect 25% and 50% differences in CPUE between samples. Common Carp CPUE peaked in June (29 fish/h), declined across the summer, and was lowest in October (9 fish/h). Bigmouth Buffalo CPUE exhibited bimodal peaks in May (16 fish/h) and October (12 fish/h), with low catches during August (2 fish/h). Common Carp size structure was largest during October (PSD of preferred‐size fish [PSD‐P] = 92) and smallest in July (PSD‐P = 58). Bigmouth Buffalo size structure was smaller in June (PSD‐P = 20) than in all other months (PSD‐P = 34). Our targets for number of fish captured and precision were typically reached within twenty‐five 15‐min electrofishing transects for Common Carp during periods of high catch rates but were not reached after 100 transects for Bigmouth Buffalo in most cases. Our results suggest that timing of sampling is important for reliably and efficiently assessing Common Carp and Bigmouth Buffalo populations. We recommend the sampling of Common Carp with electrofishing during June and the sampling of Bigmouth Buffalo during May in Midwestern shallow lakes to maximize catch rates while minimizing the influence of seasonal sampling variability.