The way water is allocated in the future, and how we find a balance between competing industries, is vital to the Northern Territory (NT) and National economies. In order to achieve this, the fishing industry and Government require a more predictive and quantitative understanding of the role of river flows in driving fisheries productivity.
This project provides the first rigorous analysis of specific flow components that drive the productivity of the barramundi and mud crab fishery in the NT. We will quantify these relationships, test a range of water extraction scenarios and explore their impact on downstream fish populations and fisheries. This will contribute to informed decision-making about future water allocations and contribute to Government policies and strategies, particularly around the current northern Australia development agenda. This project directly addresses NT FRAB Priority 3.
Previous analyses show that barramundi (e.g. Robins et al 2005; Tanimoto et al. 2012) and mud crab catches (Meynecke et al. 2012) are positively related to coarse hydrological metrics (e.g. total wet season flows). However, the mechanisms driving these relationships remain speculative and it is difficult to determine the effects of specific flow management regimes. For example, it is currently unknown if dry season flows affect fisheries production, or if there are thresholds of wet season flows which alter fisheries productivity. This project will use new, innovative biochronological techniques to better quantify the relationship between hydrological variables and the productivity of barramundi and mud crab fisheries in the NT.
The second component of the report describes an evaluation of the utility of gastric ossicles (calcified mouthparts) for direct age estimation in the Giant mud crab. Originally, we intended to use growth increments in gastric ossicles using the methods of Leland and Bucher (2017; FRDC 2014/011) to undertake analyses similar to those described above for Barramundi. However, we identified significant issues in the early stages of the project which raised concerns regarding the technique’s suitability for Giant mud crab and, potentially, other species of crustacean. In light of these concerns, the emphasis of this project component was shifted towards a comprehensive assessment of the use of gastric ossicles for direct ageing of Giant mud crab. Based on this assessment, we conclude that considerable further research on method validation is required before direct ageing of crustaceans is adopted in fishery research and monitoring. In the meantime, we caution against the use of this age estimation technique for crustaceans.