Ecological modelling of the impacts of water development in the Gulf of Carpentaria with particular reference to impacts on the Northern Prawn Fishery

Abstract

Our Gulf of Carpentaria MICE (Model of Intermediate Complexity for Ecosystem Assessments) links river flows with estuarine and marine systems and is the first integrated framework for quantifying the impacts of water resource development (WRD) across a range of ecological assets, catchment systems, scales and parameter settings. While there is scope to build on and refine this framework, we are nonetheless able to provide some considerations and recommendations with respect to water resource development implementation:
Key findings
- Changes from baseline flows due to WRDs had variable impacts on all species and catchment regions, with impacts ranging from minor through to extreme impacts under some scenarios.
- Our risk assessment classified the highest water allocation and multi-catchment WRD (WRD1) as the highest risk development, with moderate to intolerable risks predicted for all species and groups except for seagrass, and both in terms of population-level risk and fishery risk, followed by WRD2 and WRD4 (lower water allocation or single catchment WRD), both of which also predicted high risks to some populations and fisheries. WRD3 was assessed less risky because it assumes no development on the Flinders and Gilbert River catchments.
- Largetooth sawfish were predicted to show the greatest sensitivity to WRDs (due to their low productivity life-history characteristics) with risks ranked as intolerable across a broad range of alternative water extraction or impoundment scenarios.
- For common banana prawns, the Flinders River catchment emerged as the most sensitive to WRDs, consistent with previous findings from estuarine productivity studies (Burford and Faggotter 2021).
- We quantified the probability of alternative WRDs increasing the baseline economic risks to the common banana prawn sub-fishery of the Northern Prawn Fishery by computing the relative probability of occurrence of major risks (defined as risk of a bad or “unacceptable” year), severe risk (two successive bad years) and intolerable risk (fishery operations becoming unviable due to three or more consecutive bad years). We found that the risk of a bad year may more than double under some WRD scenarios.
- The Gilbert River catchment emerged as the riskiest scenario overall for barramundi abundance and catches.
- For mud crabs, the Flinders and Gilbert River catchments emerged as most vulnerable to WRDs with risks often as high as the severe risk category.
- The MICE predicted major to severe risks to mangrove habitats under some WRD scenarios, but the mangrove sub- model is more uncertain than the other groups as suitable data for validation were not available. The MICE predicted negligible risks to seagrass, although we did not account for potential increases in nutrient levels and turbidity that may be associated with WRDs.