The NSW Department of Primary Industries continues to work with the NSW commercial fishing industry to investigate structural changes to the management of commercial fisheries which will lead to improvements in efficiency and profitability. One issue that requires consideration in these deliberations is the highly variable inshore-offshore production that is linked with rainfall in coastal NSW. Such changes are exacerbated during periods of drought or flood and result in significant shifts in the behaviour of fishers. It is expected that such variations in rainfall will continue, and are likely to become more extreme, under projected climate change scenarios.

This project will examine the NSW commercial catch records and ascertain if there are patterns of endorsement holdings that are the basis of more robust fishing businesses during periods of drought or flood. We expect that many fishers will understand these patterns based upon extensive practical experience, but an empirical confirmation of such patterns will lend additional weight to any associated decisions by government and industry.

This project will also shed light upon an important facet of risk management in fisheries. The textbook economic argument that increased specialisation results in increased efficiency must be contrasted with potential lost opportunities for fisheries production in a highly variable environment. The adage "don't put all your eggs in one basket" is likely to be highly applicable for inshore and coastal fisheries in NSW. Increased specialisation will likely be associated with costs as well as benefits.

The NSW oyster industry has suffered severe economic losses during the past 20 years as the result of major outbreaks of gastroenteritis and other oyster-borne diseases. Further outbreaks will cripple the industry from immediate losses and resulting litigation.

There is an urgent need to re-examine the conditions for depuration of NSW oysters harvested in very different geographic and environmental conditions with particular reference to water temperature, salinity and turbidity during depuration. It is important to determine what limitations exist in the current technology and how they might affect purification efficiency and commercial acceptance by oyster farmers. In light of such information, there will be a need to modify the Code of Practice for Oyster Depuration. Equally important is the need to educate and train oyster farmers in proper quality assurance of oyster quality and safety, which will include optimal application of purification technology.

Current safety of oysters is assessed by the presence of E. coli as indicators of bacterial pathogens, yet the majority of oyster-borne disease is of viral origin, principally NV and more recently, HAV. Unfortunately, direct testing for human viruses in oysters is time consuming and very expensive, and will remain so for the foreseeable future. From the perspective of implementing a quality assurance program that will effectively protect public health, it is essential to have more accurate and more reliable indicator tests for the presence of human viruses in oysters. Consequently, there is a clear need to examine the relationship between the presence of bacterial indicators (E. coli), coliphages and human infectious viruses in oysters before, during and after purification. Such a study will not only clarify the behaviour of viruses during purification but could lead to a rapid coliphage assay as a more accurate indicator of human virus presence in oysters.

This research proposal developed from discussions with NSW and Queensland oyster growers who consider estuarine acidification is a cause of declining oyster health and productivity. A recently completed study of estuarine acidification and its role in fish kills, habitat degradation and outbreaks of EUS in estuarine fish, showed that the occurrence and duration of acidification events may be a potential threat to sessile organisms such as oysters (Sammut et al., 1996; 1996b; Callinan et al., 1996;1996b). The former study indicates that such associations between acidified water and poor oyster health are plausible. The proposed study is needed to test for putative associations between acidified water and oyster health and productivity problems. It will also generate other data that will be used to identify risk factors for QX disease. If an association between QX disease outbreaks and exposure to acidified water is confirmed, or other water quality variables are identified as causative factors, then appropriate water quality management can be developed. At present, attempts to manage acid sulfate soil drainage in NSW fail to recognise the water quality needs of oyster producers. Data from this study can be used to design acid sulfate soil management strategies to avoid secondary impacts on oyster health and maximise productivity.