Harvest strategy evaluation for the eastern stock of gemfish (Rexea solandri)

Abstract

The eastern stock of gemfish in south-eastern Australia is currently assessed to be overfished and to be depleted below the performance criterion established by the Australian Fisheries Management Authority (AFMA). Assessments of the stock indicate that there was a substantial decline in abundance during the late 1970s and early 1980s and that the year classes spawned at the end of the 1980s were much weaker than expected from the (estimated) stock-recruitment relationship. The performances of a variety of alternative management procedures are contrasted. The factors considered in the operating models include uncertainty about historical catches, the comparability of recent survey estimates, the form of the stock-recruitment relationship, whether variations in recruitment about the stock-recruitment relationship are auto-correlated, and the quantity and quality of the data available for assessment purposes. The management procedures differ in terms of their data needs (survey data only, survey and age-composition data) and their target levels. The results indicate that, even though yields from the fishery are likely to be low, the benefits of conducting annual surveys exceed the costs. The value of collecting age-composition data is less clear. Management procedures based on Virtual Population Analysis achieve more variable catches and are less likely to satisfy AFMA performance criteria than management procedures based on a Schaefer production model, but they achieve higher levels of 'guaranteed' catch for the industry. (C) 1999 International Council for the Exploration of the Sea.