Although methods exist for projecting the outcome of alternative management strategies when sufficient data exist to allow fitting of traditional fishery dynamics models, such approaches are typically not available when the paucity of data makes it impossible to fit such models. Such is the case for many of the finfish fisheries in south-western Australia, in which a considerable proportion of the catch has been taken by recreational fishers. For these fish stocks, current assessment must rely strongly on age composition data and mortality estimates from equilibrium-based models. The potential impacts of recruitment variability on these stocks, which are heavily exploited, have yet to be factored into management decisions. The Department of Fisheries, RecFishWest, WAFIC, and the WA FRAB have recognised that, for key demersal finfish species, there is an urgent need to assess the implications of variable recruitment and to respond appropriately when setting allowable levels of total catch. To sustain heavily-exploited stocks, it may be appropriate to reduce exploitation following periods of low recruitment to husband the survivors of earlier, stronger year classes, and thereby ensure that adequate spawning potential remains available until a further strong year class enters the fishery. Methods that employ the types of data available for fisheries in south-western Australia and by which the strengths of recruiting year classes might be taken into account in assessing an appropriate management response are currently not available to the Department of Fisheries’ scientists and are urgently needed. Generic tools and alternative operating models (models that represent our best understanding of the fish stock and fishery) are also required to assist in determining the adequacy and robustness of harvest strategies that are based on currently-available data and assessment methods.
Project number: 2008-006
Budget expenditure: $255,999.64
Principal Investigator: Alex Hesp
Organisation: Murdoch University
Project start/end date: 30 Jun 2008 - 29 Dec 2010
1. Develop a modelling approach capable of generating (through simulation) the types of biological and fishery data that would be likely to be produced by selected Western Australian finfish fisheries and which could thus be used in a "fishery simulator" to explore the effectiveness of alternative management strategies.
2. Develop a generic harvest strategy evaluation framework that employs a modular structure, facilitating the development and use of alternative operating models, monitoring and assessment methods, and decision rules.
3. Explore the effectiveness of alternative management responses to recruitment variability and to the current age composition of the stock.
Author: Alex Hesp