Connectivity between rivers and their adjacent wetlands and floodplains is an important feature of healthy, functioning freshwater ecosystems. Globally, this connectivity is often lost or compromised, leading to the loss of health and function in riverine systems. To help restore the health of Australia’s Murray-Darling Basin, the NSW Reconnecting River Country Program (RRCP) is considering the relaxation of flow limit constraints in the Murray and Murrumbidgee rivers, to allow water for environmental to be periodically delivered at higher levels to improve connectivity of rivers with wetlands and low-lying floodplains and thereby support a range of and potential environmental benefits.
We quantified these benefits using a stochastic population model developed for Golden Perch (Macquaria ambigua). The project considered four differing flow management scenarios: current operational limits and four scenarios with relaxed constraints and therefore increased flows. The model’s spatial extent spanned the southern connected Murray-Darling basin including the Murray, Edward, Darling and Murrumbidgee Rivers, represented as 8 connected populations where discreet population responses were analysed over 124 years utilising modelled flow and temperature data inputs. The model considered the best available knowledge of the ecology and biology of Golden Perch.
Modelling predicted significant benefits to Golden Perch populations under all relaxed constraints options (average increase of 20% in population size), with the highest benefits predicted under the highest level of relaxed flow constraints (30% increase in population size). The modelling also provided important insights into the population dynamics of this species, where some populations are sinks while others drive the dynamics of the whole metapopulation, highlighting the importance of source populations.
Our approach represents a significant step forward in the spatial and temporal extent of population modelling on Australian fish species. This project also demonstrates the predictive utility of population modelling as a tool to answer management questions.