The urgent need for reliable quantitative data on the habitats which are used extensively by commercial and recreational fish species during one or more stages in their life cycles has been highlighted by Cappo et al. (1998) in their report to FRDC (95/055). That report identified a deficiency in a knowledge of the following:

1. Characteristics and locations of important fisheries habitats at scales useful for research and management.
2. Life history information for fish species, related to the types of habitats occupied throughout their life cycles, and data on the densities and/or biomass of those other biotic components of fish habitats, which provide food and/or protection for fish, such as invertebrates and aquatic vegetation.
3. Habitat dynamics and ecosystem processes, including food webs, habitat use and fisheries production in soft sediment substrata, such as beaches.
4. Fisheries-habitat links, including the influences of hydrodynamic and other processes on the recruitment of commercial and recreational fish species.

The above gaps in our knowledge were also highlighted by the FRDC in its “Research Priorities for Fisheries Ecosystem Protection”, when they listed two of its strategic R&D areas as “defining major habitats in the coastal exclusive economic zone” and “the roles of habitats in maintaining healthy fisheries production, ecosystem integrity and biodiversity”.

There is a particularly urgent need to fill the above gaps because the coastal and estuarine waters of Australia are becoming increasingly exposed to the effects of numerous coastal developments, e.g. the construction of harbours, marinas and groynes, and to the destruction of habitat through other forms of activity, e.g. dredging for sand and extreme forms of eutrophication. Information on which habitats are most important to commercial and recreational fish species in these waters are required by managers so that they can introduce appropriate plans for managing and conserving those habitats.

From the information in B2, there is, for the following reasons, clearly a need to develop a recreational inland fishery in south-western Australia utilising the euryhaline black bream.
1. To provide, for local residents and tourists in rural areas, access to an outstanding angling and food fish species that occurs naturally in Western Australia and which is both hardy and adapted to living in a wide range of salinities and temperatures.
2. To increase for rural areas, which, during recent years have suffered economic decline through land degradation and salinisation, the potential for tourism.
3. To reduce the fishing pressure on natural populations of black bream, the abundance of which in some estuaries has declined precipitously during the last 20 years, presumably through overfishing (FRDC 93/082).
4. To determine whether the very different growth rates recorded for geographically isolated natural populations of black bream are due to genetic differences or differences in the environments in which they live. Such data are important for ascertaining whether it is necessary to select carefully the populations used as broodstock.
5. To explore the possibility that inland water bodies could be used for producing black bream economically on a limited commercial scale.
6. To provide an angling species in inland saline water bodies of south-western Australia which occurs naturally in the region.

The two current FRDC supported projects investigating the WA dhufish conducted at the Fremantle Maritime Center and the School of Biological Sciences at Murdoch University have identified various fish health issues for the species. In some cases these fish health issues will have implications for wild stocks of the WA dhufish and in others they may compromise the ability to commercialise the culture of the species.

Whilst health problems identified so far have been controlled to some extent in the hatchery, the ability to control these in a commercial grow-out operation will be very difficult unless a thorough understanding of the life history of the infesting organisms and the relationship to their host is known. Similarly, improved knowledge of the causal mechanisms of exophthalmia syndrome are required to permit prevention and treatment measures.

Staff at the Fremantle Maritime Centre, the Fisheries Department of WA, or the School of Biological Sciences at Murdoch University do not have the resources to quantify disease causal agents and preventative measures for the WA dhufish.

A recent report of the National Task Force on Imported Fish and Fish products (the Fish Task Force report) noted that there is a serious shortage of aquatic animal health specialists in Australia. The report identified a need to provide a continuum of expertise in this field to support developing aquaculture industries. A recent response to this issue from the Office of the Australian Chief Veterinary Officer (OCVO) emphasises that there is a considerable need for more veterinary training in fish health. This includes the development of standard diagnostic techniques for diseases of aquatic animals and the development of contingency plans for the management of aquatic disease and pest outbreaks. The proposed project addresses these issues.

There is a critical need to develop a management policy for the blue swimmer crab fishery in Western Australia, that is based on sound biological data collected for this species in this state. Since the environments in which blue swimmer crabs are caught in Western Australia are unique, it is essential that detailed biological data of this species are collected specifically for these waters. The type of biological data that are required include information on the habitat requirements, size and age composition, growth and reproductive biology of this crustacean species. Reliable data on some of these aspects (size and age composition and reproductive biology) are essentially confined to those obtained for the Peel Harvey Estuary and to those derived from catches obtained in Cockburn Sound, using a trawl net with a large mesh (Potter et al., 1983; Penn, 1977; FRDC project 95/042). From a comparison of data in these latter studies, it would appear that crabs grow to a larger size or live longer in marine waters than in estuaries. There is thus an urgent need to obtain more precise information on the biology of blue swimmer crabs in the different habitats in the marine habitats in south-western Australia.

There are no biological data for blue swimmer crabs in Shark Bay, where the fishery is developing and has great potential. Shark Bay is located at a far more northern latitude than the Peel-Harvey Estuary and Cockburn Sound, and is characterised by far warmer water temperatures. Furthermore, there are essentially no estuaries near Shark Bay, which means that this type of area which is often used as a nursery ground is not available to this portunid in the region of Shark Bay. The presence of far warmer temperatures in Shark Bay, which will presumably influence the activity, feeding, growth and reproductive biology of this species (see e.g. Hill, 1980; Sukumaran & Neelakantan, 1996), together with the type of environment found in that region, mean that it would be very dangerous to extrapolate from the results of studies further south in temperate Western Australia, or indeed from elsewhere in Australia.

It should be noted that the biological data produced by this proposal will complement a separate study of the dynamics of the fishery (both commercial and recreational) and exploitation of the series of stocks which contribute to the catch of blue swimmer crabs in Western Australia. This project proposal by the Fisheries Department Research Division, will be submitted to the FRDC in December 1997 for the 1998/99 round of grant proposals.

References

Hill, B.J., 1980. Effects of temperature on feeding and activity in the crab Scylla serrata. Marine Biology 59: 189-192.

Penn, J.W., 1977. Trawl caught fish and crustaceans from Cockburn Sound. Rep. Dep. Fish. Wildl. West. Aust. 20: 1 24

Potter, I.C., P.J. Chrystal & N.R. Loneragan, 1983. The biology of the blue manna crab
Portunus pelagicus in an Australian estuary. Mar. Biol. 78: 75 85.

Sukumaran, K. K. & B. Neelakantan, 1996. Relative growth and sexual maturity in the marine crabs, Portunus (Portunus) sanguinolentus (Herbst) and Portunus (Portunus) pelagicus (Linnaeus) along the southwest coast of India. Indian J. Fish. 43: 215-223.