Stock assessment of the EKP fishery, and the subsequent advice to management and industry, could be improved by addressing a number of issues.

The recruitment dynamics of EKPs in the northern (i.e., North Reef to the Swain Reefs) parts of the fishery need to be clarified. Fishers report that the size of the prawns from these areas when they recruit to the fishing grounds is resulting in sub-optimal sizes/ages at first capture, and therefore localised growth overfishing.

There is a need to assess alternative harvest strategies of the EKP fishery, via computer simulations, particularly seasonal and monthly or lunar-based closures to identify scenarios that improve the value of the catch, decrease costs and reduce the risk of overfishing, prior to implementing new management measures.

The project is highly relevant to FRDC priorities and directly addresses the FRDC R&D 2005-2010 Plan, namely Program 1 Natural Resources Sustainability, Challenge 1 – Natural Resource Sustainability “Maintain and improve the management and use of aquatic natural resources to ensure their sustainability”.

The proposal directly addresses the QFIRAC 2007 R&D priorities for Trawl Fisheries which specifically refer to “Undertaking management strategy evaluations for the Eastern King Prawn fishery, particularly the potential for seasonal closures…”.

It also addresses the Queensland TrawlMAC “high” research priorities in relation to improving our understanding of the stock-recruitment relationships and undertaking management strategy evaluations.

In summary, there is a strong need for this project, which addresses the high research priorities identified by FRDC, QFIRAC and the Queensland TrawlMAC. It is focused on Queensland’s most valuable fished stock, eastern king prawns.

The estuaries of Australia’s tropical rivers support commercial fisheries for finfish and shellfish valued at over $220 million per annum. There are also significant tourism-related and local recreational and indigenous fisheries for icon species such as barramundi. Development of water resources in Australia’s Tropical Rivers region is being considered for the Flinders, Mitchell, McArthur, Roper, Daly and Victoria catchments. Greater knowledge of the freshwater requirements of tropical aquatic ecosystems, including estuaries is crucial, so that the communities of catchments where water resource development occurs can be assured that the downstream effects of such development are considered and managed based on the best available knowledge.
Most research into the role of freshwater flows in aquatic ecosystems that support fish and fisheries has occurred in freshwater reaches of southern Australian rivers, except for that in the Fitzroy River Queensland, (a large dry tropical river). Conceptual models of the role of freshwater in estuaries of the Gulf of Carpentaria (GoC) and the effects on estuarine-dependent fisheries (i.e., LWA project QP155) is based on available knowledge gained from research in the Fitzroy River. However, these conceptual models lack confirmation of the underlying mechanisms, mostly as a consequence of a lack of process understanding as it occurs in GoC estuaries.

Greater knowledge of the role of freshwater flow in estuarine-dependent fisheries production in the GoC will allow for informed sustainable development of tropical water resources, with minimal impacts on fisheries resources.

1. Need to evaluate current management measures

There is a need to evaluate the current management measures applied to the scallop fishery, particularly the range of minimum legal sizes, the effects of the southern closure and the rotational closures. Precisely what are these measures achieving and are they effective? Can the value of the resource be increased with alternative management measures, within the constraints of acceptable risks of overfishing? One of QFIRAC's priorities is to look at the scallop fishery and in particular the value of protected areas, sources of mortality and stock structure.

2. Need to determine discard mortality and growth by region

Some processors are requesting DPI&F abandon the rotational spawning stock closures and lower the minimum legal size of scallops with the intention of increasing the amount of scallops fishers can retain and market. To consider any of these changes in management that could possibly lead to overfishing it is imperative that we have precise estimates of key stock assessment parameters including gear selectivity, and discard mortality.

3. Need to measure fine-scale trawl intensity

The frequency with which discarded scallops are recaptured over time and space may impact on estimates of discard mortality. Using the VMS trawl track database the frequency with which an area is trawled will be determined to guide subsequent discard mortality experiments.

1) Legal obligation.

In Australia, sea snakes are a protected species group under Schedule 1 of the National Parks and Wildlife Regulations 1994, but despite their protected status, tens of thousands of snakes are caught incidentally in the Queensland trawl fishery each year. In the Northern Prawn Fishery (NPF) it has been estimated that between 81,000 and 120,000 were caught annually in the early 1990s (see Wassenberg et al. 1994 and Ward 1996). Wassenberg et al. (2001) reported that 48.5% of sea snakes caught from research and commercial prawn trawling die as a result of being trawled. The Queensland Government and the Queensland commercial trawl fishers are legally obliged to address the problem and minimise sea snake – trawl interactions.

2) Recommendations by the Department of Environment and Heritage (DEH)

The impact of prawn trawling on the sustainability of sea snake populations on the Queensland east coast is a major concern to DEH. In their review of the strategic assessment of the Queensland east coast trawl fishery, DEH recommended to the Queensland Government that research into the impact of trawling on sea snakes be promoted, and that all reasonable steps should be undertaken to reduce interactions between protected species and the Queensland trawl fishery.

In summary there is a strong legal case in support of research that reduces the impacts of trawling on sea snake populations. In addition, addressing the DEH recommendations will help to ensure that that the Queensland east coast trawl fishery remains on the list of fisheries that are accredited for export, thus securing the continuation of the export of seafood produced from the fishery.

References

Ward TM (1996) Sea snake by-catch of prawn trawlers on the northern Australian continental shelf. Marine and Freshwater Research 47, 631-635.

Wassenberg TJ, Milton DA, Burridge CY (2001) Survival rates of sea snakes caught by demersal trawlers in northern and eastern Australia. Biological Conservation 100, 271-280.

Wassenberg TJ, Salini JP, Heatwole H, Kerr JD (1994) Incidental capture of sea-snakes (Hydrophiidae) by prawn trawlers in the Gulf of Carpentaria, Australia. Australian Journal of Marine and Freshwater Research 45, 429-443.