Commercial and recreational fishers are permitted to use gillnets in Tasmania. There are several classes of gillnet distinguished by mesh size - commercial gillnets include, small mesh, graball and shark nets, while recreational gillnets include mullet and graball nets. During the past 5 years around 150 commercial operators each year have reported gillnet use, for an average catch of 200 tonnes of scalefish. Recent information for the recreational sector is limited though recreational netting remains popular, with over 10,000 net licences issued in 2009. Previous surveys indicate that recreational fishers target much the same species as commercial operators.

Over the past decade there have been several management initiatives, including a prohibition on night netting for most areas and, more recently, the introduction of maximum soak times. These initiatives have been designed to improve gillnetting practices, and reduce wastage and impacts on non-target species. Despite this, there have been conspicuous declines in the abundance of several key gillnet species along with increasing community concern about the ecological impacts of gillnetting. This concern has been particularly evident in the debate surrounding the introduction of marine protected areas, with gillnetting identified as a key threat to biodiversity. Furthermore, in the 2009 Scalefish Fishery review DPIPWE identified the need to develop strategic policy in relation to no-netting areas to address issues including resource sharing, wildlife interactions and stock management.

In view of the above, there is an urgent need to better understand how recent management initiatives have influenced netting practices, and to objectively assess the risks and impacts on target and non-target species. Ultimately such an understanding will be pivotal in informing the on-going debate over the future management of gillnetting in Tasmania.

The ability to detect infected animals is an essential requirement in animal health monitoring and surveillance. A major problem of testing farmed and wild fish is the absence of simple diagnostic tests for the detection of asymptomatic carrier fish. Where tests are available, they are resource intensive and time consuming such as the heat+corticosteroid stress test for furunculosis in salmonids. This test is used for disease control measures in eastern Canada and has been instrumental in limiting spread of furunculosis to sea cage farms (Olivier 1992). Active surveillance of animal populations is considered an important approach in animal health monitoring (Stark 1996) and is of particular relevance with publication by the Office International des Epizooties of its guidelines in the International Aquatic Animal Health Code (Anon 1997) for defining disease-free status.

Demonstration of freedom from disease, both covert and overt, within a region or a country, can be an asset when selling live and uncooked product in markets overseas. As global trade develops, Australia will need to demonstrate freedom from disease not just as a marketing strategy but as an essential requirement of trade and as a means of protecting or limiting the spread of disease.

This project aims to develop a hybrid technology derived from the food industry. It will require adaptation and refinement for use with fish pathogens and development of test protocols for screening adequate numbers of fish. The use of specialised enrichment culture media with the sensitive and specific techniques of PCR should provide a useful and sensitive tool in active surveillance of fish populations and fish products. This technology will also have application in screening ornamental fish entering Australia as well as uncooked fish products.

Detection of bacterial pathogens using immunological markers or DNA are termed proxy tests since the presence of the pathogen is inferred. Proxy tests pose two major problems: firstly what is the relationship of the proxy measure to the intact target pathogen and secondly, what is the biological significance of the proxy test? Validation of proxy tests is a recognised problem that if unresolved can seriously restrict the use of such tests (Hiney 1997). The proposed project solves many of these issues of validation: the primary test requires amplification of the target pathogen by culture and hence is not a proxy test. Detection of the target pathogen after culture utilises a secondary proxy test but it can be internally validated by secondary culture as required. The test system will be evaluated against farmed populations of fish to determine the significance of findings, a pre-requisite for external validation. Correlations of this type have not been undertaken previously and the strategies proposed in this project represent a realistic attempt to convert bench tests into practical and robust diagnostic tools.

References:

Anon (1997) International Aquatic Animal Health Code. 2nd edit. Office International des Epizooties, Paris.
Hiney M. (1997) How to test a test: methods of field validation for non-culture based detection techniques. Bull. Eur. Ass. Fish Path. 17:245-250
Olivier G (1992) Furunculosis in the Atlantic provinces: an overview. Bull. Aquacul. Assoc. Canada 92-1: 4-10.
Stark K D C (1996) Animal health monitoring and surveillance in Switzerland. Aus. Vet. J. 73:96-97.