Kills in the Darling: assessing the impact of the 2018-20 mass fish kills on the fish communities of the Lower Darling-Baaka River, a large lowland river of south-eastern Australia

Understanding the impacts of extreme events is essential to effective fisheries management. During the summer of 2018-19 millions of native fish died in Lower Darling-Baaka River adjacent to Menindee, New South Wales, Australia. Hypoxia during a period of protracted low flow, triggered by climatic events, was responsible for the fish kills. From June 2019 to March 2020, further broader-scale fish kills occurred throughout similar to 600 km of the Darling-Baaka River as disconnected refuge pools contracted and water quality deteriorated. This study examined the status of the remnant fish populations, compared the fish assemblage of the Menindee fish death reach with an unaffected reach and monitored change of the fish community over 18 months after the initial fish kills. Significantly lower abundances of Murray cod (Maccullochella peelii), bony herring (Nematalosa erebi), carp gudgeon (Hypseleotris spp.) and freshwater prawn (Macrobrachium australiense) were captured within the Menindee fish death reach compared with the unaffected reach. Varied responses were observed in species abundances within the affected reach in the 18 months after the initial fish kills, attributed to the various life-history traits and reproductive strategies. The results presented highlight a fish community in continued stress. Continued monitoring will guide and track the effectiveness of recovery management interventions in the region.