Since 2018 there has been a sequence of major fish kills in the lower Darling (Baaka) River system that have decimated native fish populations in the local area. While the proximate causes of the fish kills have been extensively studied in a series of inquiries and published research, to date there has been a lack of research focused on quantifying longer-term trajectories of populations in this region and or quantitative assessments of population change under likely future scenarios of climate and river management.
To more adequately inform future management plans, estimates of native fish population recovery and potential extinction risks, are required. This includes examining the combined effects of climate change on flow permanence, declining habitat availability, local catastrophic fish kills due to poor water quality, and barrier passage for fish populations. Here we develop a spatially explicit dynamic fish population model to assess the population viability of four freshwater fish species (Murray cod, Golden perch, Bony bream and Common carp) of the Darling (Baaka) River under hydrological conditions observed in the past ~40 years. By analysing the persistence characteristics of riverine waterholes during cease to flow events and simulating future hydrological conditions we found key drivers of population viability across the Darling (Baaka) River.
Our results show that two large bodied long-lived species, Golden perch and Murray cod, are at risk of local extinction under multiple future scenarios. These model predictions are reinforced by analyses of population age-structure, which shows that average rates of population growth within the system are well below replacement. Future management recommendations for population management in the system include, flow delivery that aims to reduce cease to flow duration and waterhole turn over and implementing upstream fish passage solutions are important steps to have populations that persist in the Darling Baaka River.