Enhancing fishery assessments for an Australian abalone fishery using commercial weight-grade data

Abstract

Effective management of commercial fisheries is dependent on the reliability of fishery assessments that, in turn, are determined by the quantity and quality of the available data. Data on the length-structure of the catch provide important information on exploited stocks, but representative sub-sampling is difficult to achieve, especially where numerous licence holders fish over large areas. This study evaluates the potential for routinely collected, commercial, weight-grade data to overcome this challenge and enhance assessment of the Western Zone blacklip ( Haliotis rubra) and greenlip ( Haliotis laevigata) abalone fisheries in South Australia. Current weight-grade data for blacklip abalone are inaccurate. However, the accuracy, rigour and consistency of the data for greenlip abalone confirm they are sufficiently reliable for aiding fishery assessments on this species. The greenlip abalone data were highly representative of the catch and the fishery and have been obtained in a consistent manner for >20 years. Changes in the composition of the grades in the catch provide a meaningful measure of change in the harvested stock. Similarly, measures of mean weight and number harvested, derived from the weight-grade data, are valuable as additional indices of stock status. These attributes substantially enhance the credibility of these data for use in assessing changes in stock status through time, and suggest these data should be used to supplement current assessments of this species. The value of the weight-grade data would increase substantially if the resolution was improved by using automated weighing and grading systems. The analysis of weight-grade data, routinely collected from numerous fisheries, is likely to benefit their assessment.