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 loss and compromise of habitat is a problem that affects all Australian commercial and recreational fisheries (Zann et al. 1996). A recent review (funded by FRDC) of fisheries habitat research in Australia (Cappo et al. 1998) found that more action is needed to rehabilitate degraded habitats, of which coastal wetlands are particularly important. Cappo et al. 1998 also found that understanding of impacts on fish stocks was hampered by lack of knowledge regarding natural variation in populations and habitats.

Priorities for further habitat research have been emphasised by Cappo et al. (1998) and are reflected in FRDC’s Ecosystems Protection Program. This project has particular implications for protecting and enhancing fisheries habitats in the following specific areas:
1. Defining and monitoring the utilisation of a major habitat type in the coastal zone and assessing the role of that habitat in fisheries production;
2. As a trial for a self-sustaining management strategy that will actively encourage fisheries habitat rehabilitation, regardless of the site/fishery involved; and
3. By providing a direct benefit to fisheries habitats and therefore the associated fish stocks in the local region.

There is currently specific concern in the Southern Shark Fishery regarding the status of school shark stocks, with catches falling steadily from 2026 tonnes in 1986 to 749 tonnes in 1997 (Walker 1998, Punt and Walker 1998). However, there is a differential between the status of school shark stocks and those of gummy shark, which are considered to be sound. Thus there is a clear need to introduce measures which assist in rebuilding school shark stocks without adversely affecting sustainable catches of gummy sharks. There is also an identified need to protect school shark pre-recruits, which appear to be increasingly hard to find.

School sharks give birth during November and December in protected bays and channels on low-energy coastlines in Victoria and Tasmania (Olsen 1954; Stevens and West 1997). Although newborn sharks are found outside these areas, school shark nursery areas are regarded as 'critical habitat' for this species. This nursery habitat type has suffered significant loss throughout southern Australia, initially as a result of farming practices and subsequently from coastal development. Hence, in addition to concerns about the effects of fishing on the breeding stock, there is concern that loss of school shark nursery habitat may be causing further stock reduction or inhibiting management attempts at rebuilding the stock. Thus, there is a critical need to protect, restore and/or enhance nursery habitats for juvenile school shark as part of a strategy to improve recruitment to the fishery and contribute to restoring stocks.

Many of the important nursery areas for school shark (and other fish species) have been altered through human activities. For example, the 'State of the Marine Environment Report for Australia' indicates that several of the most important school shark nursery areas have lost large areas of seagrass. In Victoria, Western Port Bay has lost 17,800 hectares (and 85% of the seagrass biomass) and, in Tasmania, the Pittwater Estuary has lost 1201 hectares and Norfolk Bay has lost 2148 hectares.

Action to arrest the trend in degradation of school shark 'critical habitat' and to rehabilitate lost habitat is essential if school shark is to be a resource that can be used sustainably. The shark fishing industry initiative to inundate Black Swamp with seawater is the first attempt at rehabilitation of a school shark nursery area. This initiative will also provide additional habitat and potential nursery area for other commercial (MacDonald 1997) and recreational (Hall and MacDonald 1986) species abundant in Corner Inlet (Gunthorpe, in prep). Some of these other species which have high commercial value or are sought after by recreational fishers include snapper, gummy shark, southern garfish, greenback flounder, flathead and King George whiting.

Corner Inlet is an excellent location for trialling restoration of coastal wetlands and estuarine fish habitats, given:
- it was formerly acknowledged as an important juvenile school shark nursery habitat;
- the drained coastal wetlands of Corner Inlet formerly provided nursery areas and adult habitat for many other fish species utilised by commercial and recreational fishers;
- extensive areas of such habitat have been lost in the inlet through the construction of sea walls, resulting in mangrove, seagrass and saltmarsh communities being converted to pasture;
- there is significant potential for restoration of additional areas of the inlet outside the specific area involved in the trial;
- the project has generated widespread local support and enthusiasm from a variety of stakeholders, including offshore and inshore fishermen, landholders, local council and the community; and,
- nationally there may be hundreds of drained coastal wetlands that could be restored and managed through a similar approach should the trial prove successful. This wider potential application is demonstrated by the breadth of support for this project from fisheries managers in other states.

Gunthorpe, L. (in prep). Corner Inlet fish habitats – 1998 (Compiled by Fish Habitat Assessment Group) (Fisheries Victoria: Melbourne).

Hall, D. N., and MacDonald, C. M. (1986). A survey of recreational fishing in Corner Inlet and Nooramunga, South Gippsland. Marine Fisheries Report No. 8. (Fisheries and Wildlife Service: Melbourne).

Olsen, A. M. (1954). The biology, migration, and growth rate of the school shark, Galeorhinus australis (Macleay) (Carcharhinidae) in south-eastern Australian waters. Australian Journal of Marine and Freshwater Research 5, 353-410.

MacDonald, C. M. (1997). Corner Inlet - Nooramunga fin fisheries 1994. Fisheries Assessment Report Series . Report No. 3. 50 pp. (Department of Natural Resources and Environment: Melbourne).

Punt, A. E., and Walker, T. I. (1998). Stock assessment and risk analysis for the school shark Galeorhinus galeus (Linnaeus) off southern Australia. Marine and Freshwater Research 49 (in press).

Stevens, J. D., and West, G. J. (1997). 'Investigation of school and gummy shark nursery areas in south eastern Australia.' 77 pp. (CSIRO Marine Research: Hobart.)

Walker, T. I. (1998). Can shark resources be harvested sustainably? A question revisited with a review of shark fisheries. Marine and Freshwater Research 49 (7).

Zann et al. (1996). The State of The Marine Environment, Report for Australia, GBRMPA.

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.