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 spawning dynamics and early life history are largely unknown for BSC and GMC in NSW, as are spawning areas, sources and sinks, important juvenile nurseries, and the effect of environmental variability on both spawning and recruitment. While this has led to some limitations to management and uncertainty in the past, NSW have recently launched two major management initiatives for the species for which this information is essential: 1) management of commercial BSC and GMC harvest through share-linked catch quota; and 2) fisheries enhancement for BSC and GMC.

In 2017, the Commercial Fisheries Adjustment Program has seen the NSW Government subsidise the investments of many fishing businesses to access catch quota for BSC and GMC. Quota allocation depends on scientifically-based assessment of Total Allowable Catch (TAC). At present the only source of information on which to base TAC is historic catch and effort, but these are highly variable and the mechanistic factors underlying this variation are unclear. The recent NSW Marine Stocking Fishery Management Strategy outlines the development of release programs for both BSC and GMC. Effective implementation of this strategy relies on a thorough knowledge of the requirements of young crabs and the factors affecting their recruitment such that recruitment limitation can be identified and releases targeted to address it (see Taylor, 2017). Through a review of existing work on these species in other states, and consultation with managers and industry, we have identified targeted research questions that will directly enhance the capacity of NSW DPI-Fisheries to design and implement effective harvest management, fishery enhancement and restoration programs for BSC and GMC. The need for this information is especially evident in the attached letters of support from commercial and recreational stakeholders, and the contribution of $250K cash from the NSW Recreational Fishing Saltwater Trust.