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.