Project number: 2015-012
Project Status:
Current
Budget expenditure: $286,000.00
Principal Investigator: Alison J. King
Organisation: Charles Darwin University (CDU)
Project start/end date: 30 Jun 2015 - 29 Jun 2017
Contact:
FRDC

Need

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.

Objectives

1. Undertake ageing and biochronological measurement of barramundi otoliths and mud crab ossicles, and collate NT catch and environmental data (e.g. river discharge).
2. Develop rigorous, regionally specific empirical models to quantify the relationships between fisheries productivity and various metrics of freshwater inflow using advanced statistical techniques.
3. Provide research findings to industry and government for a scientifically defensible and robust basis for decisions on the future use of water in northern Australia in relation to fisheries resources.

Final report

Authors: David Crook John Morrongiello Alison King Brendan Adair Mark Grubert Thor Saunders Michael Douglas Brien Roberts
Final Report • 2021-02-01

Summary

The research presented in this report was led by Charles Darwin University and conducted in collaboration with the University of Melbourne and the Fisheries Division of the Northern Territory (NT) Department of Primary Industries and Resources (DPIR). A novel statistical modelling framework based on age and growth data from otolith analyses was used to examine relationships between recruitment and growth of Barramundi and a range of climatic and river hydrology variables in four rivers in the NT. We found strong evidence that the magnitude of Barramundi recruitment was linked to the strength of the Australian Monsoon Index. This relationship offers potential to predict future fisheries yields three years in advance based on observed meteorological phenomena. We used river-specific hydrology analyses to predict the effects of water abstraction on Barramundi recruitment and growth. Scenario analyses predicted strong negative effects of water abstraction (>30% in several scenarios) on Barramundi recruitment, with the predicted effects variable among river systems. Results of the analyses were communicated to DPIR and the NT Department of Environment and Natural Resources (DENR) via a series of presentations to promote their use in future fisheries management and water resource planning.
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.

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