Correcting bias introduced by aerial counts in angler effort estimation

A critical part of most any roving angler survey is angler effort estimation. Various methods have been proposed and implemented to calculate this important parameter, and one of the most effective for estimation over large areas utilizes aerial counts of anglers. In this paper, we describe effort estimation methodology used for the lower Juniata River and the lower and middle Susquehanna River Creel Survey conducted in 2007 by the Pennsylvania Fish and Boat Commission. Daytime angler effort estimates were calculated using an augmented aerial survey, which included both aerial counts and data collected by creel agents on the ground. Interview angler effort data, obtained via a modified roving ground survey, was used to produce estimates of daily effort distributions, which were the basis for expanding instantaneous aerial counts to daily effort estimates. We present two ratios which ameliorate biases introduced by the aerial survey. An angler-to-people ratio, calculated from the ground data, accounts for shore persons who are not anglers, and a ground-truthing ratio corrects for people and boats inadvertently omitted from the aerial counts. Variance estimation and effort results from the survey are discussed as well.