Multi-decadal trends in large-bodied fish populations in the New South Wales Murray-Darling Basin, Australia

Context. Native fish populations in Australia's Murray-Darling Basin (MDB) have experienced severe declines since European settlement. Information on their status is needed to guide management and recovery. Aims. To quantify trends in MDB fish populations in New South Wales (NSW) from 1994 to 2022. Methods. Relative abundance, biomass, and size structure were examined using generalised additive mixed models at NSW MDB and river catchment (valley) scales for five native species (Murray cod, Maccullochella peelii; golden perch, Macquaria ambigua; silver perch, Bidyanus bidyanus; Macquarie perch, Macquaria australasica; freshwater catfish, Tandanus tandanus) and one alien species (common carp, Cyprinus carpio). Key results. There was strong inter-annual variation in relative abundance, biomass and population structure for all species. At the Basin scale, relative abundance of Murray cod, golden perch and common carp increased across the time series, with no clear trends for silver perch, Macquarie perch or freshwater catfish. Patterns in relative abundance, biomass, and population structure were variable among valleys for most species. Conclusions and implications. Although native fish populations in the MDB remain degraded and face escalating threats, recent increases in the abundance of some native species are an encouraging sign that integrated restoration efforts can improve the outlook for native fish.