River flow is crucial in the life cycle of prawns that support the Northern Prawn Fishery (NPF), as well as iconic tropical species (e.g. mud crab, barramundi, grunter, and threadfin salmon) of importance to commercial, recreational and Indigenous fisheries, and species with high conservation (e.g. sawfish) and cultural value. Substantial interest in developing irrigated agriculture across northern Australia is reviewed in a recent FRDC report (Kenyon et al. 2018). Water extraction to support agriculture will modify natural flow regimes that support estuarine and coastal fisheries. The trade-offs associated with proposed water resource allocation are currently unknown and research is needed to support decision making related to alternative strategies for managing water resources effectively for both agriculture and marine production and biodiversity conservation. Quantifying these trade-offs entails evaluating how altered river flows might affect the fishery and ecological values. Most work to date has focused on the hydrological rather than ecological aspects (and particularly how to quantify aspects such as the minimum water requirements for ecological components) as managers otherwise need to make decisions without sufficient research and given limited timeframes. Although previous and recent projects such as NAWRA have evaluated the qualitative impacts of changes in river flows on ecological assets, there is a need to quantify impacts both for consideration by affected commercial, recreational, indigenous and other sectors, as well as to provide water resource managers with quantitative estimates such as the minimum water requirements to maintain ecosystem structure and functioning. Such analyses are also complicated by the fact that each catchment is different, and hence models and the associated recommendations need to be tailored to be specific to each catchment area, and there is currently no suitable ecosystem model at the appropriate scale and incorporating key relationships.

The work is needed to:
(i) critically review the available literature on environmental factors influencing crab fisheries;
(ii) update analytical relationships between catch and environmental factors to include the extreme climate events experienced in the past 10 years in the GoC, and for a broader range of environmental factors than previously considered;
(iii) expand jurisdictional stock modelling to a more biologically appropriate scale and support cross-jurisdictional collaboration;
(iv) test the ability of model results to inform management of the relative importance of fishing pressure compared to environmental factors;
(v) develop reference point concepts suitable for adaptive harvest strategies for crab fisheries in northern Australia.

The project will provide information at a broad spatial scale (i.e., GoC) for crab species with different life histories and potentially different responses to environmental factors. It will compare the declining catches of mud crabs with the anecdotally reported increasing catches of blue swimmer crabs in the GoC.

Recent increases in blue swimmer crab catches in the GoC needs to be investigated to clarify which species are present and to assess their vulnerability to fishing.

The adaptation of an existing crab population model will be a case study that potentially could be applied to the Queensland east coast and other crustacean species. The current work will assist in determining whether the NT GoC mud crab fishery warrants management intervention as a consequence of environmental factors. The recent closure of blue swimmer crab fisheries in WA highlights the potential of environmental factors to seriously impact a stock to the point where fishing needs to be removed (Johnston et al 2011).