The giant cuttlefish Sepia apama, which annually migrate to northern Spencer Gulf, South Australia, has recently undergone substantial declines in abundance and attracted significant media and public attention. Whilst it is accepted that the Marine Stewardship Council (MSC)-accredited SGPF, which has been operating and reducing its effort for almost 50 years, has not been the cause of the decline, several consecutive years of diminishing numbers and a particularly low population estimate in 2013 requires all efforts to be made to minimise the incidental catch of this species. The SGPF has been pro-active in taking steps to minimise interactions during this species’ annual migration. One such measure is the commitment to investigate the development of a bycatch reduction device (BRD). During its development, it would be prudent to also ensure that the BRD also reduces the bycatch of blue swimmer crabs Portunus armatus, because these require additional handling and, owing to their exoskeletons, physically damage the soft-bodied prawns and cuttlefish.

A recent pilot study (2013/052) identified the parameters within which a successful BRD should exist. This work involved testing two Nordmøre-grids over a few deployments, yet yielded promising results (i.e. both designs reduced the numbers and weights of cuttlefish, crabs and total bycatch, and one of the designs maintained prawn catches). Through rigorous testing of refined versions of these Nordmøre-grids across larger spatial and temporal scales, the proposed study aims to produce an optimal design for potential implementation in the fishery.

1) There is need to incorporate environmental data in understanding larval dispersal and stock-recruitment relationships for two major crustacean fisheries, prawns and blue crabs, in SG.
2) There is a need to identify regions critical for spawning and settlement success for prawns and blue crabs.
3) There is a need to develop optimal harvesting strategies for prawns during the pre-Christmas fishing period, to maximise catch and minimise the impact on future recruitment to the fishery.
4) There is a need to understand the effect natural variations in physical environmental parameters (including winds and tides) have on larval ecology and recruitment success for prawns and blue crabs in SG.
5) There is a need to develop tools to inform on the threat for major fishery resources from climate change by understanding impacts of temperature change on stock-recruitment relationships for these fisheries.

This project addresses a need for information on the effects of human-induced disturbance on important coastal habitats. Aims of the public and of the fishing industry have congruence in seeking to maintain healthy aquatic ecosystems. Ecological sustainable development is a frequently expressed aim of modern fisheries management but management objectives relating to the ecological consequences of commercial fishing are rarely underpinned by defensible quantitative information. It is therefore difficult, if not impossible, to determine if fisheries are being prosecuted in an ecological, sustainable manner. So little is known of processes structuring sub tidal ecosystems that is difficult to formulate coherent and meaningful policies governing activities in Australian aquatic habitats. More importantly, it is difficult to identify environmental performance indicators to assess the status of individual fisheries. In reality, the interactions of harvesting on marine species and co-occurring boita are poorly understood. This is particularly the case for inshore fisheries in which harvesting occurs within the euphotic zone and the potential for significant alteration in the food chain, mediated by fishing, is real. There is a clear need to identify human-induced processes that may damage coastal ecosystems and that may affect the viability of nearshore fisheries.

Fisheries in Gulf St Vincent claim that the productivity of fisheries is being affected by changes to the habitat.

This project is one of a suite of research programs aimed at evaluating the ecological consequences of fishing. Other research programs on prawn fishing discards and of the consequences of abalone fishing are proposed for South Australian ecosystems and address similar needs. The linkages and common focus on coastal ecosystems will reinforce the outcome and the utility of the proposed research. A key outcome will be the identification of quantitative yardsticks of performance in relation to reasonable standards of ecological sustainable fishing practices. This outcome is needed to reinforce management plans with the quantifiable performance indicators relating to ecological sustainable development that are presently lacking for Australian fisheries.