1) The ecosystem effects of fishing need to be understood in order to work towards an EBM model for the Spencer Gulf. The South Australian government’s Marine Manager’s Forum has identified Spencer Gulf as the first area in SA for the development of a marine management plan. Better information on impacts of fishing will reduce the reliance of managers on the precautionary principle in developing management plans.
2) The important results from FRDC project 98/225: Prawn fishery by-catch and discards: fates and consequences for a marine ecosystem, are an understanding of the major components of the food chain in the trawled areas of the Gulf and the identification of the major scavenger groups on discarded by-catch. There is a need to obtain data on population impacts in order to develop trophic dynamic models.
3) A prerequisite for energy-flow models is population data outlining life history parameters, growth, migration and immigration and standing stock of, in principle, all the major species.
4) Previous research by this investigator shows that the quantitatively important scavengers on discarded by-catch in the Spencer Gulf prawn fishery are Degens leatherjackets, sealice (non-parasitic highly aggressive isopods and amphiopods), blue crabs, large stingrays and Port Jackson sharks. The effects of discarded by-catch on the population structure of these species need to be understood with the aim of developing an ecosystem model.
5) The impact of fishing on marine ecosystems (target and by-catch) on sharks, skates and rays is a world-wide problem (Stevens et al. 2000). 50% of the global catch is taken as by-catch. The catch of non-target species can have an impact at the population and ecosystem levels, particularly the removal of top predators. Elasmobranchs are at the top of the food chain in the Spencer Gulf and are important by-catch in the prawn fishery. The ecosystem level effects of fishing on the populations of these species are unknown. Discarded by-catch is susceptible to mortality. This mortality, including sub-lethal effects and post discard mortality, needs to be measured in order to predict ecosystem effects.
6) To adopt the principle of ecological sustainability in the prawn fishery, change negative public perceptions of environmental impacts, and improve fishing practices.
7) To enhance the research capacity in environmental research with emphasis on biological resource utilisation.
(Stevens, J.D., Bonfil, R., Dulvy, N.K. & P.A. Walker 2000. The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES J. Mar. Sci. 57: 476-494.)