Developing a robust new empirically based harvest strategy for gummy shark
The Gummy Shark (GS – Mustelus antarcticus) fishery has lands an annual catch worth approximately $13 million and comprises 15-20% of the value of the South East Shark and Scalefish Fishery (SESSF). The fishery has a long history of stable catches, which successive analyses attribute to recruitment...
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| Format: | Report |
| Language: | English |
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Biospherics Pty Ltd
2011
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| Online Access: | https://researchportal.murdoch.edu.au/esploro/outputs/report/Developing-a-robust-new-empirically-based/991005543524207891 https://researchportal.murdoch.edu.au/view/delivery/61MUN_INST/12136079570007891/13137102420007891 |
| Summary: | The Gummy Shark (GS – Mustelus antarcticus) fishery has lands an annual catch worth approximately $13 million and comprises 15-20% of the value of the South East Shark and Scalefish Fishery (SESSF). The fishery has a long history of stable catches, which successive analyses attribute to recruitment remaining stable since the inception of the targeted fishery in the early 1970s, and there has been little investment in research on the fisheries ecology of Gummy Shark. However, the fishery displays a number of unusual, and poorly understood dynamics, which to some extent are incompatible with standard stock assessment assumptions. An outcome of this project is that it is now clearly understood by Shark Resource Assessment Group (SharkRAG) members that the while Gummy Shark assessment reliably estimates the stable long term trend in recruitment, estimates of adult biomass are poorly informed by data and relatively unreliable. This shared feature of successive GS assessments was of less importance prior to the adoption of the Commonwealth Harvest Strategy Policy and the de facto decision that GS Total Allowable Catches (TAC) would be based on estimates of adult biomass. Since that decision the reliability of estimate of adult GS biomass has become a matter of some importance. The documents prepared and presented through this project to SharkRAG and the South East Management Advisory Committee (SEMAC) and the discussion these documents have supported in those forums, have enabled a shared understanding to be developed of the poor basis estimated adult GS trends provide for setting TACs. The GS assessment model contains virtually no data on adult biomass and consequently model estimates of current adult biomass are largely unconstrained by data. It emerges that the form of Density Dependence Mechanism (DDM) assumed for the assessment model largely determines the estimated trend in adult biomass and current levels, and a wide range of plausible DDMs exist which we have no informed ability to distinguish between. Despite ... |
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