Properties of Catch Rates Used in Analysis of Angler Surveys

Abstract

Abstract On-site angler surveys commonly yield data on fish catch, fishing effort, and their variances for a sample of anglers. The ratio of catch to effort, or catch rate, often is multiplied by an independent estimate of total effort to calculate total catch (with its confidence interval) throughout the fishery. The most frequently used measures of catch rate are the ratio-of-means estimator (mean catch per angler divided by mean effort per angler) and the mean-of-ratios estimator (mean angler's catch rate). Bias and misleading confidence intervals are associated with use of ratio estimators, and the best catch rate measure for estimating total catch has been uncertain. We used statistical theory and simulation modeling to demonstrate that the most appropriate estimator (least bias, truest confidence interval) depends on the method of sampling. The ratio-of-means catch rate is better when anglers are sampled with equal probability at the completion of their trips (as in access point surveys). The mean-o...