Variable Catchability and Statistical Power in Standard Largemouth Bass Surveys

Variable catchability can decrease power to detect changes in abundance with fisheries survey data.  Resource agencies adopt standardized sampling protocol to reduce sampling variability, although these methods are rarely validated.  We estimated electrofishing catchability of Largemouth Bass in two small Ohio reservoirs with mark-recapture techniques over a series of sampling events following Ohio Division of Wildlife (DOW) standard protocol.  We then simulated statistical power to detect a 50% decline in abundance under variable and constant catchability when comparing two single years and two five-year blocks.  Statistical power was similar between variable and constant catchability scenarios.  When comparing two single years statistical power was low (≤ 0.65), but was high (≥ 0.80) when comparing five-year blocks, highlighting the importance of long-term monitoring.  These results suggest that catchability does not vary enough to affect statistical power in small Ohio reservoirs when data are collected using the DOW protocol, validating spring electrofishing as a standard assessment method.   These results also help manage our expectations of electrofishing relative abundance data; multi-year analyses of long-term datasets may be more appropriate than testing for changes in abundance from one year to the next.