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.

Giant Australian cuttlefish, the largest cuttlefish species in the world, is widely distributed across southern Australian waters. Through most of its range it breeds on inshore rocky reefs, but it is renowned for forming the single largest known breeding aggregation of any cuttlefish species in the world. Each winter thousands of cuttlefish aggregate at Point Lowly in Upper Spencer Gulf (USG) to spawn. Estimates of abundance and biomass of spawning cuttlefish have indicated that population density at the aggregation site has declined through time with the most dramatic decreases occurring in 2011 and 2012. The magnitude of this decline has raised concerns about the sustainability of cuttlefish and highlighted the paucity of information relating to the fine-scale population structure and dispersal of this species within USG, as most studies have concentrated on the adult component of the population. The dispersal of hatchlings away from the spawning site and residence as sub-adults is currently unknown. Recent research investigating the broader-scale population structure suggested that the USG population was genetically isolated from the rest of the State, and may constitute a separate species (Gillanders and Donnellan, ARC Linkage project). This degree of isolation imparts a greater conservation focus on the species and highlights the importance of identifying the ecological/environmental factors that are driving the observed population decline and whether certain life-history stages are more vulnerable than others.

Declines in world prawn prices and rising fuel costs are contributing to a shift in fishing practices in the NPF and an increase in targetting of valuable byprduct groups such as bugs and squid. Little research has been done on byproduct in the NPF or in other tropical prawn trawl fisheries. The 2002 catch of byproduct was almost 250 t (AFMA) and comprised of four main groups (squid, cuttlefish, bugs and scallops) of at least eight species. However, the catch of squid alone has been over 400 t in some years (AFMA). The impacts of trawl catch on these groups have never been assessed. This situation is common among many Australian fisheries, where despite the value of byproduct being substantial, they lack sufficient data to undertake specific assessments or even to evaluate options for their management. Thus, there is a need for methods to help identify management options for groups that are data poor like byproduct species in the NPF. New approaches developed in this project will be of value to other Australian trawl fisheries especially the Torres Strait Trawl, East Coast Trawl and Western Australian prawn trawl fisheries. Operational advice from this project would contribute to at least two possible management strategies: the first would be to control fishing on byproduct through species-specific stock assessments. The second would be to control effort on byproduct through spatial and temporal closures, by identifying the key areas and seasons when these byproduct groups are most vulnerable. The most efficient approach to assess the relative merits of alternative management options is to adapt existing trawl impact assessment scenario models to account for non-target catch in their strategy evaluations.

Coastal areas of Australia, especially those close to urban areas, are under increasing pressure from industrial and tourism developments, and the associated infrastructure to support them. These shallow-water coastal and estuarine areas will also continue to be the focus of attention by the recreational and commercial fishing sectors. An understanding of the impacts of damage to key intertidal habitats will allow managers to minimise the adverse impacts and developmental degradation on Australia's fisheries resources.

There is currently no detailed information available on the specific effects of loss or damage to intertidal estuarine habitats on the animal assemblages that utilise these habitats, despite the recognised importance of the habitats and the benthic invertebrates to fisheries resources. Studies which have examined the effects of damage to subtidal habitats have shown important links to fisheries utilising these habitats (e.g. Sainsbury et al., 1993). Similar studies should be a priority for critical intertidal estuarine habitats. Although this project focuses on damage to intertidal habitats caused by bait-harvesting, the results of this work will be applicable to other sources of damage to these habitats, providing an important database establishing causal relationships between effects on the physical structure of the habitat and impacts on the associated animals.