Refining and Applying a Maximum-Count Aerial-Access Survey Design to Estimate the Harvest Taken from New Zealand's Largest Recreational Fishery

Abstract

We used a maximum-count aerial-access survey design to estimate the 12-month recreational harvest of snapper Chrysophrys (Pagrus) auratus (also known as squirefish) taken by New Zealand's largest recreational fishery. To provide a count of all boats fishing on a given day, the spatial extent of the 3,800-km² Hauraki Gulf embayment was surveyed from the air on a random stratified selection of survey days at the approximate time of maximum effort. Anglers were also censused at a subset of the available access points on the same day. The ratio of the aerial count to the number of interviewed parties who claimed to have fished at the time of the overflight was used to expand the observations of landed catch and to estimate the total catch taken by all fishers returning to all access points. Pairing an aerial count with a creel-survey-derived profile of effort on each survey day provides two advantages. First, only one flight is required to estimate the overall level of effort on each day, which is beneficial given the costs of operating aircraft. Second, the relationship between these two data sources can be used to estimate the level of effort and harvest on all survey days, including those days when flights are cancelled due to low clouds or other nonrandom events. This approach is currently the preferred harvest estimation approach in New Zealand, and it has since been used to assess the snapper harvest from management areas with coastlines in excess of 2,000 km long.

Received February 7, 2011; accepted July 28, 2011

ACKNOWLEDGMENTS

We acknowledge and thank Martin Cryer, who first introduced us to the aerial-access approach and provided support and advice at many times. We are also very grateful to Ken Pollock, who reviewed an early draft of this paper and directed us to previous studies that had used or discussed the maximum-count method, and for many useful insights he provided. Thanks are also due to David Middleton, who pointed out that there was a far more parsimonious version of the analytical approach than we had previously considered, and to Chris Francis for his advice on how to implement a correction for finite population sampling in our bootstrapping procedure. We are grateful to Darren Parsons for many useful comments on an early draft of this paper and to two anonymous reviewers who provided comments that considerably improved this paper. The data used in this paper were collected as part of the New Zealand Ministry of Fisheries’ contracts REC200202, REC200401, REC200501, and REC200502.