Prawn resources underpin some of the most economically important fisheries in Australia and form the basis of very important recreational fisheries. Ecologically sustainable development of fisheries resources partly depends on catching species at optimal sizes and there is considerable concern that the gears being used in NSW’s commercial and recreational prawn fisheries catch them at sizes smaller than that which optimises biological yield.

Prawn fisheries in NSW (and the world) have attracted enormous attention in the past few decades over their by-catch of non-targeted species – especially juvenile fish. In NSW, this led to the development, implementation and legislation of various gear-based solutions like the Nordmore Grid and square mesh panels (see attached publication list). A major by-catch issue remaining for NSW’s prawn fisheries concerns the by-catch and discard of unsaleable sizes of school and king prawns. Currently, large numbers of small prawns are discarded well after capture (sometimes even after cooking) through the process of “riddling” which involves passing the prawn catch over a sieve to separate large and small individuals. This is considered a major waste of a resource – especially since it is known that, for fast-growing prawns, undersize individuals could be expected to reach a desirable size in a relatively short time. Unfortunately, virtually no research has been done on the selectivity of school and king prawns in any of the gears used to catch them (i.e. prawn trawls, haul nets, set pocket nets and snigging nets in commercial fisheries; and dragnets and scoop nets in recreational fisheries). All are thought to catch large numbers of very small school and king prawns that are discarded well after capture. If excluded from nets underwater, these prawns should, in a relatively short period of time, provide substantially improved catches of the more desirable and valuable sizes of prawns.

In 1998, Broadhurst, Larsen, Kennelly and McShane developed a codend made entirely of small square mesh to reduce the discards of small western king prawns in Gulf St Vincent, South Australia. The current application is for funds to develop full square-meshed codends and other methods to decrease the discard of small prawns throughout the many commercial and recreational prawn fisheries of NSW.

Currently there are about 180 licensed silver perch growers in all states; however, only about a third of these are producing fish commercially. Although a small number of farms achieve high production rates, most farms are inefficient and not producing anywhere near their potential. Survival, growth and production rates are much lower, and FCR's higher than achievable with good husbandry and management. Fish are being lost from disease and poor water quality, and growth rates are perceived by some farmers to be "slow".

Consultation with industry has identified that research into winter diseases and health management is a high R&D priority.

Diseases, in particular those caused by infectious agents, are recognised as an important threat to the viability of finfish aquaculture. In 1996/97 a pilot monitoring program aimed at identifying diseases causing significant production losses in silver perch was conducted on a coastal zone farm in north-eastern NSW. Results suggested that growth rates were reduced by ecto-parasitic infestations and by adverse water quality conditions. More recently, in 1998 and 1999, there have been reports of serious disease problems that have caused significant losses on some silver perch farms. These have included regular outbreaks of fungal diseases during winter, particularly in the cooler, inland areas of eastern Australia. It appears that some, or most of these outbreaks are not just the result of poor husbandry. The fungal disease, winter saprolegniosis is a serious problem in the large channel catfish industry in the USA, and relatively new winter fungal diseases have been reported in freshwater fishes in other parts of the world. There is strong evidence of a similar, but currently undescribed winter fungal disease in silver perch. Clearly there is a need to describe the major diseases, including important emerging diseases, on silver perch farms and identify their causes. Cost-effective control and prevention measures can then be developed.

More broadly, as the industry matures, silver perch farmers are becoming increasingly aware of the importance of systematic, cost-effective measures aimed at reducing disease-related losses to acceptable levels. However, no such validated programs are currently available to the industry. To fill this vacuum, it is essential that "Health Management Programs" i.e. generic disease control and prevention programs, are developed, validated and extended to farmers. These programs can be modified to suit the needs of individual farms and integrated with routine management activities. On individual farms, the programs will comprise (a) broadly targeted measures based on established principles and aimed at general disease prevention, early detection and control, with (b) specifically targeted measures aimed at reducing losses caused by important diseases (e.g. winter diseases) occurring in the farm's geographic area.

The production capacity of silver perch (10 tonnes/ha/year), the established culture techniques, the large number of inefficient farms, and the ready availability of sites provide the basis for a dramatic increase in production of silver perch over the next 5 to 10 years. However, research to address the current disease problems is required to maximise the value of previous research and to enable the industry to realise its full potential.

With the decline in several other sea urchin fisheries around the world, there now exists a good opportunity to develop a large and valuable fishery for purple and red sea urchins in NSW. In addition, there is also interest in the further development of the purple urchin fishery near Mallacoota in eastern Victoria, and the white urchin fishery in Port Phillip Bay. This interest is evidenced in both NSW and Victoria by substantial capital investment in factories to process sea urchins and their roe. If these urchin fisheries could be further developed within an appropriate management framework, it could also lead to significant benefits for the abalone fishery, particularly in NSW, because of the interaction between the two species.

Because of the limited development of this fishery to date, it provides an ideal opportunity to assess stocks of sea urchins prior to any major depletion by fishing. Sampling techniques have already been developed for sea urchins in barren habitats, and could easily be transferred to habitats where commercial fishing will be concentrated. Such assessments may be particularly important considering the evidence from other urchin fisheries, where large virgin stocks have been rapidly depleted with only low rates of recovery from the recruitment of juveniles.

Preliminary information from NSW suggests a large proportion of the sea urchin population does not contain high quality roe. Unless high quality roe can be reliably collected, the costs of processing sea urchins may restrict development of the fishery. Two main techniques have been used in other fisheries to improve the supply of food to sea urchins on reefs, and hence the quality of roe that can be harvested. If these techniques could be adapted for sea urchins in NSW, significant improvements in yield and value would be possible. Further, as the simple, large scale removals are already being used in the industry, there is also a need to detect their impacts on other species.

It has become apparent to commercial divers within the NSW abalone fishery that previously productive areas of reef are now supporting high densities of sea urchins, and correspondingly low densities of abalone. This change has contributed, together with pressure from the commercial and recreational fishery, illegal poaching, disease and pollution, to a decline in the sustainable yield from the population. The current development of the sea urchin fishery in NSW provides the opportunity to re-establish populations of abalone on once productive areas of reef over a large spatial scale. Natural recolonisation of areas of reef will be limited because of the restricted dispersal of larvae from their parents.

A variety of techniques are already being used to help re-establish populations of abalone on depleted areas of reef in NSW. These include the clearance of sea urchins to allow natural recovery, together with the transplantation of broodstock to help increase the speed of recovery. All these techniques are very labour-intensive. The deployment of seed produced from wild abalone provides a significantly more powerful technique to rapidly enhance populations of abalone on depleted reefs over a large-scale. Protocols for the conditioning, spawning and rearing of blacklip abalone are already well established and provide the framework for the year-round production of seed. Techniques for the large-scale deployment of seed have been developed in other states, but recent advancements in our knowledge of settlement substrates suggest further improvements can be made. Similarly, deployment techniques will need to be adapted for the unique conditions on reefs in NSW, and particularly the presence of the sea urchin, Centrostephanus.

With the development of techniques to allow the successful, large-scale release of abalone seed to coastal reefs in NSW, there are likely to be significant benefits to the associated fisheries. In particular, the potential exists for increases in the sustainable yield of the fishery of up to several hundred tonnes per year, or several million dollars.