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The Research

Environmental Benefits - Portunus pelagicus as a biomonitor of cadmium

Cadmium is an inorganic toxicant of great environmental and occupational concern which was classified as a human carcinogen in 1993. A number of previous studies have randomly selected biota for analysis of metals in a given system and attempted to interpret the results to reflect the contaminated nature of the area. Studies such as those conducted through this project highlight the need to conduct controlled bioaccumulation trials prior to the conduct of such monitoring programs. This work has shown that P. pelagicus has the potential to be utilised as a biomonitor of cadmium pollution in the surrounding environment given the assessed bioaccumulative ability and the ecology of the species.

Social Benefits - Recreational Fishery - Blue Swimmer Crabs

Recreational fishing is substantial but is not well quantified in New South Wales. Fishing occurs in much the same locations as the commercial fishery, although it is mainly targeted at the shallower inshore areas. Capture methods include pots, tangle nets (witches hats, dilly nets), rakes, dab nets, baited hoop nets and drop nets. For recreational fishing, there are fishing gear retrictions in New South Wales. Recreational fishers are only allowed up to 5 Witches' Hats and one rigid trap per person. Recreational fishers are only allowed to take a maximum of 20 crabs per person per day.

Economic Benefits

The Blue Swimmer Crab is widely known as a commercial and recreational fishing species. Significant catches of this animal make it one of the preferred seafood species in the country; indeed its distribution enhances this reputation as it can be found almost all around the country, except for stretches of the southern coastline and Tasmania. The Blue Swimmer Crab is a decapod crustacean in the same Order as lobsters and prawns. The Blue Swimmer and the Mud Crab are the favoured table species. One of the objectives of this research is to assess the viability of producing Soft-Shelled Crabs as a popular seafood cuisine.

Commercial Fishery - Blue Swimmer Crabs

Moreton Bay, Hervey Bay and other inshore areas of southern Queensland account for approximately half of the commercial catch of Blue Swimmer Crabs in Australia. Other important commercial grounds are along the New South Wales coast and include Wallis Lakes and the lower Hunter River. West Coast, Spencer Gulf and Gulf St Vincent in South Australia, and the Peel Harvey Inlet and Cockburn Sound near Fremantle and the Swan-Avon River near Perth in Western Australia are all important commercial grounds. Streaky Bay in South Australia periodically supports a small fishery.

Fishing takes place on/off shore sand banks, in channels and deeper water up to 25m deep. Catches are highest from January to March (Summer). Blue Swimmer Crabs are caught in cylindrical wire traps or pots and folding traps, preferably baited with mullet. Hoop nets, drop nets and sunken crab gill nets are also used. Rakes and dab nets are used in very shallow water.

Blue Swimmer Crabs form a significant proportion of the by catch many prawn trawlers land in Queensland. It has been estimated that between one third and one half as many crabs are caught in the targeted pot fishery. Blue Swimmer Crabs are caught incidentally with rock lobsters and in finfish fisheries. Due to the seasonal nature of the fishery, Blue Swimmer Crab fishers usunally engage in other fishing activities as well, such as catching the Spanner/crab (Ranina ranina).

Commercial markets of the Blue Swimmer Crabs

Most of the crabs marketed within Australia is as whole cooked crab or crab meat. There is a small export market for Blue Swimmer Crabs: this is mainly to Japan. The average 1991-92 price per kg at the Sydney Fish Markets was A$4.86 (green) and A$5.54 (cooked).(Kailola et al 1993).

Soft-shelled Crab Production

Potential methods for the production of soft-shelled crabs were trialled using Portunus pelagicus. It was found that crabs held physically separated in a single aquaria, with both eyestalks ablated, resulted in the highest percentage of crabs moulting per unit time, (mean of 48% as opposed to 20% for controls). Crabs held as individuals, and completely isolated from others, again with both eyestalks ablated, resulted in the fastest mean days to moult when compared to crabs held in groups with double eyestalk ablation (19.0 days +/- 2.4). The injection of moulting hormone, 30 degrees Celsius temperatures, single eyestalk ablation and male only treatments were found to have little effect on the initiation of moulting in this species. A method for the treatment and holding of P. pelagicus for the production of soft-shelled crabs is proposed.

removing crab from a tangled net

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