A more precise stock assessment is needed for the Shark Bay Snapper Fishery in view of the wide confidence limits around the previous assessment in the mid 1980s. Assessment is needed now because of the increased level of recreational effort on the stock and the implication in the new management plan that the commercial TAC must be reduced to enable recreational catches to be included in an overall TAC. The material is available for a precise stock assessment but resources are required for working up the data and performing the stock assessment.
Knowledge of the degree of variability in annual recruitment is required to assess the feasibility of a cost effective constant TAC management policy for the future.
Market preferences for fish of particular sizes, and the minimum legal length, can result in significant discarding. The mortality of these discarded fish and effects on the stocks need to be factored into TAC calculations.
A minimal cost method needs to be devised for routine future monitoring of the fishery.
Final report
The investment in this project has resulted in a substantially more extensive set of age composition data than would have otherwise been possible. This in turn has underpinned stock assessment modeling that has provided the basis for determining that the commercial fishery for snapper in Shark Bay needed a substantial decrease the total allowable catch. The modeling was able to determine that the stock was at a low size following a period of low recruitment during the late 1990s. The suspected low recruitment, evident once the age date were collated, and anticipated negative effects on the stock were both quantitatively described; this mathematical treatment has been a critical input to the series of management meetings for the fishery. The significant outcome for this project was that there was no potential to increase yields in the fishery. The fishery is considered to be sustainable since the reductions in catch were instigated. The effort and catch levels typical of the 1990s were curtailed to allow the stock to recover – this ongoing maintenance of the fishery at a level that will allow the stock to increase in size, rather than implementing a complete closure associated with a more seriously depleted stock of snapper, is directly attributable to the research undertaken in this project. The occurrence of infrequent but drastic recruitment failure, as demonstrated in this project, dictates that ongoing monitoring of age-composition will be required to manage this fishery.
Keywords: pink snapper, recruitment, age-structured model, cohort analysis, risk assessment.
