The Importance of Validating the Duration of Fishing Trips: Are Harvest Rates from On-Site Recreational Fishing Surveys Unbiased?

Abstract

Harvest rates are often used as indicators of fishing quality and in the estimation of total harvest in some on-site survey designs. The unbiased estimation of harvest and fishing effort is critical for calculating accurate harvest rates. On-site survey designs allow survey clerks to validate harvest data directly. This harvest validation assumes that the level of intentional deception by fishers is relatively small. Therefore, validating angler-generated estimates of trip duration is important because this can provide evidence that harvest rates and other variables derived from effort data are also unbiased. Also, one can partition effort and harvest within trips to calculate directed harvest rates for different target species or species groups, knowing that the angler-generated estimates of total trip length are not contributing systematically to any bias in the directed harvest rates. We examined the accuracy of trip duration estimates reported by trailer boat fishers in the marine waters of New South Wales, Australia. Comparing these angler-generated estimates with observed records of actual trip duration demonstrated that the angler-generated estimates were empirically unbiased both for estimates in terms of party-hours and those in terms of angler-hours. These findings have several implications for the interpretation and analysis of survey results. We therefore recommend that angler-generated estimates of trip duration be validated for different recreational fisheries; moreover, reliable reference points should be incorporated into all interview protocols because they can minimize the bias in self-reported estimates of fishing effort. The validation of trip duration and harvest rate data are vital for convincing fisheries managers and stakeholders that surveys can provide reliable information about a fishery.