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.
The Bigmouth Buffalo Ictiobus cyprinellus is a long‐lived catostomid with ecological and commercial harvest value. Management of Bigmouth Buffalo relies on accurate age data for population dynamic assessments (recruitment, growth, and mortality), but between‐reader precision of nonlethal aging structures compared to otoliths has not been assessed. We analyzed age bias and between‐reader precision of ages estimated from pectoral and dorsal fin rays relative to lapillus otoliths for Bigmouth Buffalo (n = 115) captured from shallow natural lakes in Iowa. Maximum agreed age was 21 years for otoliths, 15 years for pectoral fin rays, and 14 years for dorsal fin rays. Ages estimated from pectoral fin rays were the most precise (CV = 12.6%; average percent error [APE] = 8.9%), followed by dorsal fin rays (CV = 16.1%; APE = 11.4%) and otoliths (CV = 21.5%; APE = 16.5%). Pectoral fin rays also had higher exact agreement between readers (37%) and higher agreement within 1 year (77%) compared to dorsal fin rays (35% exact; 69% within 1 year) and lapillus otoliths (17% exact; 61% within 1 year). Both dorsal fin rays and pectoral fin rays underestimated age relative to otoliths, which resulted in younger population age structures and larger mean length‐at‐age estimates. Our results suggest that biologists can use dorsal and pectoral fin rays as viable nonlethal structures for younger fish (up to 10 years for dorsal fin rays; up to 13 years for pectoral fin rays), whereas otoliths can be difficult to age but are necessary to accurately determine age for older individuals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.