How Does Spatial Variability, Rewards, and Tag-Loss Impact Tag-Recapture Estimates of Exploitation Rate?

Accurate estimates of exploitation rate are essential to the management of exploited fisheries. Further, few have specifically demonstrated how and by what degree assumptions and estimates impact tag-recapture estimates of exploitation rate.  Here we simulated a suite of candidate study designs for high- and variable-reward tagging studies, exploring a range of sample sizes, exploitation rates, tag-related mortality rates, tag-loss rates, proportions of double-tagged fish, and spatial variations in fish density, tag releases, and fishing effort.  We calculated the uncertainty, biases, and reward costs of these candidate study designs to determine the most cost-effective approach to accurately estimate exploitation rate for red snapper in Alabama waters. Our simulations demonstrated that using all high-reward tags was more cost-effective than using variable-reward tags and that distributing tags uniformly over the study area when the true spatial distribution of the population and fishing pressure varied over that area can drastically bias exploitation rate estimates.  These results suggest that prior knowledge of the population’s true spatial distribution over the study area is needed to ensure accurate estimates. We suggest this approach be used for future tag-recapture studies to ensure the most cost-effective approach is used to produce reliable and accurate estimates of exploitation rate.