Fish diversity and abundance before and after a wildfire: A case study from an Australian river

Fires have a range of physical and chemical effects on aquatic systems which impact species in different ways. Empirical studies on wildfire in aquatic systems are relatively scarce but provide crucial information to guide managers. We studied how wildfires in 2019–2020 influenced fish in the Mannus Creek, which is a tributary of the Upper Murray River Catchment, New South Wales, south-eastern Australia. We sampled fish in unburnt, partially burnt, and completely burnt reaches 1 year before fire and 1 year after fire using a before–after control–impact study design and continued to monitor burnt sites after a further 18 months. Our aim was to document responses to, and potential recovery from, wildfires by all fish species, but particularly the endangered Macquarie perch (Macquaria australasica). Richness and abundance decreased in the completely burnt reach 1 year post fire, while no discernible changes were found at partially burnt and unburnt reaches. Macquarie perch were completely absent from the burnt reach, and the prevalence of other fish species such as alien redfin perch (Perca fluviatilis) decreased. Consistent results were observed after 2.5 years, indicating that a return to pre-fire fish abundance and community composition had not occurred at the conclusion of the study. By taking advantage of a rare opportunity to study fish assemblages before and after a fire using a before–after control–impact study design, our results can be used to inform management decisions for fish in this system. Additionally, this study contributes to advancing our understanding of fish responses to, and recovery from, wildfires in freshwater ecosystems.