Evaluation of Standard Sampling Techniques for Estimating Abundance and Size Structure of Fishes in Standing Waters

Six lakes and impoundments in Iowa, USA were sampled using multiple gears (i.e., fyke-nets, gill nets, beach seine, trawl, electrofishing) to determine the influence of sampling methodology and season on catch-per-unit-effort (CPUE), proportional size distribution (PSD), and the number of samples required to obtain 125 stock-length individuals for 12 species of recreational and ecological importance.  The species evaluated represented a range of gear selectivity from species sampled with multiple gears to species predominately sampled with a single method (e.g., largemouth bass Micropterus salmoides).  Mean CPUE generally peaked in the spring and fall due to the effectiveness of the gears used and fish habitat use.  Mean PSD was consistent among seasons for black bullhead Ameiurus melas and yellow bullhead Ameiurus natalis, but decreased from spring to fall for white bass Morone chrysops, bluegill Lepomis macrochirus, and black crappie Pomoxis nigromaculatus.  The mean number of samples required to obtain 125 stock-length individuals was minimized with fall gill nets for five of the 12 species evaluated (e.g., walleye Sander vitreus, yellow perch Perca flavescens, channel catfish Ictalurus punctatus).  Our results provide relative comparisons between several recommended standard sampling methods and illustrate the effects of seasonal variation on estimates of population characteristics.