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Technical annual report 2000-01



Technical annual report 2000-01


Dept. of Regional Development, Primary Industry, Fisheries and Resources technical annual report; Department of Regional Development, Primary Industry, Fisheries and Resources technical and annual report; Reports; PublicationNT; Technical bulletin (Northern Territory. Dept. of Primary Industry and Fisheries) ; no. 295




Made available via the Publications (Legal Deposit) Act 2004 (NT).






Agriculture -- Northern Territory -- Periodicals; Fisheries -- Northern Territory -- Periodicals

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Dept. of Primary Industry and Fisheries

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Technical bulletin (Northern Territory. Dept. of Primary Industry and Fisheries) ; no. 295



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Department of Primary Industry and Fisheries 276 A comprehensive National Survey of Recreational and Indigenous Fishers (NSRIF) is being undertaken during 2000/01 Indigenous Fishing Mud crabs are believed to be a significant food source for coastal indigenous Australians. Section 53 of the Fisheries Act guarantees indigenous people the right to utilise the fish and aquatic resources in a traditional manner. Indigenous people are entitled to use recreational fishing gear to crab, but spearing or hand harvesting is often utilised. No information has been gathered on this sector, but the NSRIF 2000 survey will provide some details on catches taken by indigenous fishers. Fishing Tour Operators (FTO's) FTOs are licensed to conduct guided and charter fishing tours. Only recreational fishing gear can be used and the catch may not be sold, traded or bartered. The same pot and possession limits apply as for the recreational sector. FTO licences are issued free of charge, are not transferable and currently there is no limit on the number of licences issued. Of the 150 licensed FTOs, none reported targeting of mud crab as their primary fishing activity in 1999, although operators will fish for mud crab for their clients on request in conjunction with other fishing activities. In 1999 reported catch was in the vicinity of one tonne with around 20 % of this figure released. Aquaculture Successful production of juvenile crabs from larvae is the focus of current research at the Darwin Aquaculture Centre and survival rates are approaching what may be considered economically viable. Considerable work is still required on the commercial nursery production of mud crabs, the growout of large crabs and adult nutrition. However, it is anticipated that commercialisation of research results is possible and this project has now received additional support from the Fisheries Research and Development Corporation. Research The NT Mud Crab Research Program commenced in 1990. Over the past ten years a great deal of information has been collected on the growth, recruitment, migration and mortality of the mud crab. A sound understanding, of the biology of the target species and its interactions within the ecosystem, as well as the dynamics of all sectors of the fishery, are fundamental requirements in managing a fishery in a sustainable manner. In 1996 Professor Carl Walters, a world-renowned stock assessment scientist, was consulted to lead an initial assessment of the mud crab fishery. Analysis methods used included general analysis of trends in the commercial catch and effort data combined with estimation of fishing mortality using swept area analysis and a relatively new habitat/density method. Seasonal patterns of recruitment and a fishery dynamics model were also used to confer estimates of fishing mortality. The workshop results estimated exploitation rate for this fishery was around 70 percent of the adult population. High exploitation rates are indicative of crab fisheries worldwide where species exhibit short life spans, early maturity and high fecundity. Dr Walters' analyses were based on the response of the fishery to the estimated heavy exploitation in conjunction with species biological characteristics and current fishing practices. Another important finding was the confirmation that analysis of catch and effort data did not provide sufficient detail for realistic stock size estimation for this fishery. He strongly advocated the development of a fishery independent method of assessing this fishery. In following recommendations of the 1996 assessment, a National workshop was held in Darwin in 1999 to re-assess current research. A major outcome of this workshop was the development of a five-year national strategy for mud crab research, recommending a number of strategies including the development of new methods to estimate stock size Research in 2000 DPIF has been developing and testing techniques for the past three years using depletion and mark recapture methods. This work is about to be extended across the Territory and northern Queensland with the granting by the Fisheries Research and Development Corporation of $659,000 funding for a three-year