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 methods for estimation over large areas utilizes aerial counts of anglers. In this paper, we describe effort estimation methodology used for a creel survey conducted by the Pennsylvania Fish and Boat Commission in the lower Juniata River and lower and middle Susquehanna River during 2007. Daytime angler effort estimates were calculated using an augmented aerial survey, which includes both aerial counts and data collected by creel agents on the ground. Interview angler effort data obtained via a modified roving ground survey were used to produce estimates of daily effort distributions, which were then used to expand instantaneous aerial counts to daily effort estimates. We present two ratios that 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 that are inadvertently excluded from the aerial counts. Variance estimation and effort results are then discussed.