Mud crabs (Scylla serrata) are a highly prized natural resource, with the volume and value of the 2004 (national) commercial harvest exceeded 1500 tonnes and $20 million, respectively. The recreational and indigenous take of this species is also significant, with estimates for the 12 month period starting May 2000 in the order of one million crabs.

There have been widespread fluctuations in mud crab landings in recent years. For example, the commercial harvest in the NT increased from ~600 tonnes in 1997 to 1100 tonnes in 2001, then dropped to 300 tonnes in 2005. This variability is probably due to a combination of fishing activity and the environment, but the extent to which each factor influences the mud crab catch is unknown. Identification of the drivers of recruitment and stock abundance would enable resource managers to implement harvest strategies based on predicted yields.

The ability to predict mud crab yield depends on the collection of appropriate biological and environmental data, one of which being the magnitude of recruitment. This requirement corresponds to Phase 3 of the National Strategy for Research on Mud Crabs, which recommends the 'development of a fishery independent index of stock abundance based on a juvenile pre-recruit index'. It also ranks as a high priority for the Northern Territory Strategic Plan for Fisheries Research and Development 2007-2011.

To ensure that future mud crab recruitment models are widely accepted and robust, it is essential that research and management agencies across northern Australia first agree on the best approach to implement Phase 3 of the National Strategy. This will be achieved through a national mud crab research network and workshop.

Diagnostic competence in the identification of Vibrio species is of growing concern with the expansion and diversification of aquaculture in Australia. The urgent need to improve diagnostic capacity has been identified as an essential goal in the SCFA Research Priorities for Australian Fisheries & Aquaculture. Under AQUAPLAN improved diagnostic capacity in aquatic animal diseases was also identified as a major national goal under Projects 3.1 Surveillance & Monitoring, 4.2.9 Diagnostic Resources, 6.2.3 Development of New Diagnostic Tests. The National Workshop on Aquatic Animal Health: Technical Issues (FHMC 1999) identified improved diagnostic capacity for Vibrio species as a matter of priority. More recently, Aquatic Animal Industry Stakeholders nominated the identification of Vibrios as a priority need for funding under the Federal Government Budget Initiative, 'Building A National Approach To Animal And Plant Health' (AQUAPLAN, Business Group (FHMC Sub-Committee, Steering Committee of the FRDC Aquatic Animal Health Sub-Program).

Of major concern is the drive to establish health surveillance programs for aquatic animals. A surveillance program already exists for salmonids in Tasmania and similar programs for abalone in Tasmania, Victoria, South Australia and Western Australia have been identified as a priority need by the FRDC Abalone sub-programme. Similarly, a health surveillance program has been proposed for rock lobster. A major weakness however of these schemes is the lack of diagnostic capacity in veterinary laboratories servicing these health programs (Anon 1999). Given that Vibrio species form over 60% of the bacterial flora associated with these major aquaculture species the usefulness of these proposed surveillance schemes is severely limited.

Competence in identification of Vibrio species is an essential pre-requisite in any surveillance program. It provides the basis to assess the significance of findings, is a means of monitoring populations for the emergence of specific pathogens and underpins successful disease management strategies through the selection of appropriate antibiotics, probiotics or vaccines.

The difficulties identifying Vibrio species were highlighted through a National Fish Disease Bacteriology Workshop (FRDC 00/149). All participating laboratories confirmed the low success rate identifying Vibrio species isolated from aquatic animals and found most identification systems either inefficient, cumbersome or unreliable. Participants endorsed strongly the need to improve diagnostic capacity for Vibrio species.

References
Anon (1999) Gap Analysis of Research for Australian Fisheries and Aquaculture. Report for the Research Committee, Standing Committee for Fisheries and Aquaculture
FHMC (1999) Report of the Workshop on Aquatic Animal Health: Technical Issues. 7-9 December 1998, Attwood, Victoria

This project provides the opportunity to develop a new mud crab aquaculture industry for tropical and sub- tropical Australia. It will provide the crablets needed by pioneering farmers to run the first grow-out trials.

Industry has identified the need to commercialise this technology, as can be seen by the involvement of Seafarm and McRobert Aquaculture Systems participation in this project.

Seafarm is determined to secure a reliable supply of crablets for its Queensland operation, following the initial success of the first crop of crablets recently grown and harvested from its ponds. The company has stated its intention to diversify into mud crabs, in addition to its core prawn farming business.

McRobert Aquaculture Systems is aiming to get involved with the supply of crablets to both Australian and international markets, using its new tank system. It is also keen to ensure its new tank system is fully field tested for mud crab larval culture, so that it can be marketed on a sound,scientific basis.

Aboriginal groups across northern Australia have expressed great interest in becoming involved with mud crab aquaculture development. This project will provide for the supply of commercial quantities of mud crablets, which will support their future involvement.

Both the Northern Territory and the Queensland Government agencies are dealing with a steady stream of inquires regarding the availability of crablets and also the release of mud crab farming technology. This project will help meet that demand.

Mud crab aquaculture will be the focus of both industrial scale aquaculture (similar to prawn farming) development and of appropriate, ecologically friendly farming systems for coastal aboriginal communities.

In time mud crab aquaculture will enable the marketing of mud crabs, both for the local and export markets to become consistent, reliable and of an assured quality. It will also provide the opportunity for the development of a range of products including soft shell crab, crabs of a variety of sizes and a range of crab meat products.

Scaling up of research results to commercial hatchery and nursery systems will overcome two of the major obstacles to development of mud crab aquaculture in Australia identified in the draft mud crab industry development plan (which was an attachment to our previous application this year).

This project will support diversification of pond based marine aquaculture in tropical and sub-tropical Australia.

Any animal which is being farmed intensively will encounter a range of health challenges. Identifying disease agents and developing effective management strategies for them is critical. Control of bacteria loading in larval culture was identified in the ACIAR project as a key barrier to overcome in the commercialisation of mud crab culture. This project contains a health component, which will benefit from preliminary work undertaken by Dr John Norton at QDPI Oonoomba over the last few years.

This project is a vital first step in the development of the mud crab aquaculture industry in Australia. Future activities will involve work on digestion, nutrition and grow-out system design to fully commercialise this farming sector.

An examination of which fisheries species are sustained by seagrass plant production has been highlighted as a major research priority in the recent reviews of fisheries habitat research gaps by Cappo et al. (1997) and Butler & Jernakoff (draft report to FRDC). The recommended method in Butler & Jernakoff for tracing seagrass production to fisheries species is stable isotope analysis. Coastal and fisheries managers currently consider seagrass to be valuable, nevertheless there are many seagrass meadows under threat and still being lost. An argument can be developed, supported by current scientific evidence, that many important fisheries species are not reliant on seagrass and that their numbers actually increase upon the decline of seagrass. Estuarine and offshore fisheries species that do not appear to be dependent on seagrass might actually be so, but indirectly; they may be deriving their food from animals in a trophic web that is sustained by energy (carbon) and nutrients (e.g. nitrogen) transported from seagrass meadows. Another estuarine habitat, mangrove forest, has previously been touted as generating plant production that drives food webs elsewhere in estuaries and offshore. Recent evidence from Australia and Asia suggests this is not so; mangroves seem to sustain only species living in mangrove areas. The question whether seagrass production is the major source of primary production sustaining fisheries production needs answering. The best method for tracing where fisheries species gain their nutrition is stable isotope analysis.

The proposed research will be done in Moreton Bay and Hervey Bay. These bays are of extraordinary importance to Queensland fisheries, with Moreton Bay alone comprising up to 30% of the total Queensland catch of inshore recreational and commercial species (Tibbetts & Connolly 1998). There are also important fisheries in deeper waters adjacent to these bays. Both bays have extensive areas of seagrass, but also mangroves, saltmarsh and occasional reefs offshore. They are also suffering ongoing seagrass loss.

Coastal areas of Australia, especially those close to urban areas, are under increasing pressure from industrial and tourism developments, and the associated infrastructure to support them. These shallow-water coastal and estuarine areas will also continue to be the focus of attention by the recreational and commercial fishing sectors. An understanding of the impacts of damage to key intertidal habitats will allow managers to minimise the adverse impacts and developmental degradation on Australia's fisheries resources.

There is currently no detailed information available on the specific effects of loss or damage to intertidal estuarine habitats on the animal assemblages that utilise these habitats, despite the recognised importance of the habitats and the benthic invertebrates to fisheries resources. Studies which have examined the effects of damage to subtidal habitats have shown important links to fisheries utilising these habitats (e.g. Sainsbury et al., 1993). Similar studies should be a priority for critical intertidal estuarine habitats. Although this project focuses on damage to intertidal habitats caused by bait-harvesting, the results of this work will be applicable to other sources of damage to these habitats, providing an important database establishing causal relationships between effects on the physical structure of the habitat and impacts on the associated animals.