In Western Australia, and now elsewhere, there has been considerable interest in marron farming for over two decades. Many schemes have come and gone and the highly optimistic attitude which once prevailed has gradually been replaced by a more realistic approach to marron aquaculture. While, for example, it was once considered that appropriate site selection would allow marron to be cultured to marketable size (120 g) on a yearly basis (Morrisey 1976), it was later realised that at least at intensive pond culture densities achievement of 120 g average weight in Western Australia was not possible even on a two-year schedule (Morrisey 1984(a)).

Most serious commercial interest in marron farming has been with pond and dam culture but there is still little clear evidence to the would-be marron farmer. Proposed management and pond designs are yet to be tested as full-scale enterprises. Reasons cited for the failure of many marron farming schemes include predation by birds and other animals, cannibalism, climatic and weather variability and extremes, and, increasingly, operator inexperience. Underlying such explanations is the fundamental fact that pond and dam ecosystems are extremely complex and unpredictable. There is a growing appreciation that marron are sensitive organisms which are intolerant of environmental extremes.

In 1981-82 the cost of fuel and oil in the Northern Prawn Fishery amounted to 25% ($M23.65) of the total costs for a prawn trawler (Hundloe 1984). In the East Coast Prawn Fishery, fuel and oi 1 amounted to 24% ($M9.77) of the costs (BAE 1984). In recent years the dramatic rise In fuel prices has prompted many people to look closely at ways of reducing fuel costs. Much of this work has been directed towards improving the engineering performance of trawl gear. Van Marlen ( 1982) showed that total gear drag could be reduced by using larger meshes in the fore parts of midwater trawls. Chopin ( 1982) suggested that US shrimp trawls could have gear drag reduced by increasing the mesh size of the fore parts of the trawl. The design of more efficient otterboards (Karlsen 1982), (Lee and Mel lwane 1982), (Wray 1986) could also reduce the total gear drag as might the correct choice of angle of attack (FAO 1974), (Wray 1986).

The large variation in net designs, otterboard sizes and otterboard angles used in similar prawn fisheries in Australia has led many fishermen to question the choice of particular combinations of trawl gear.

This paper is the result of a joint submission by the Spencer Gulf and West Coast Prawn Boat Owners Association and the Australian Maritime College, Launceston, Tasmania to the Fishing Industry Research Trust Account (FIRTA). The performance of different combinations of conventional trawl gear used In the Spencer Gulf Prawn Trawl fishery Is compared with three East Coast prawn trawl gears.