The Upper Murrumbidgee River holds the largest population of the endangered Macquarie Perch (Maccas) in NSW, and one of the largest in Australia (Lintermans 2023). The population has a 95 km long ‘recruitment reach’ where regular monitoring demonstrates annual recruitment. Approximately 30 km upstream of the top of the recruitment reach is Tantangara Dam, which diverts 90–99% of annual natural (pre-impoundment) flows to the adjacent Eucumbene catchment as part of the Snowy Hydroelectric Scheme. Genetic analysis of finclips collected in 2020-2023 revealed extremely low effective population size, declining genetic diversity, high inbreeding, and low between-site connectivity within the reach. At the most upstream sampling site effective population size (Ne) was <5-10 individuals, and genetic diversity was low. Genetic diversity was highest at the most downstream monitoring site with Ne >120 (Pavlova et al. 2024). To improve genetic diversity and reconnect Macca subpopulations within the reach, a program of ‘within river’ translocations (shuffling) has commenced with a pilot project in 2025 moving 52 fish, followed by a refined approach in 2026 which moved another 91 individuals. To avoid impacts on donor sites, only juvenile and subadult fish have been moved to date with the program anticipated to run for another 2 years. A review of the environmental flow releases has recommended that annual flow releases be increased to 30 % of ‘natural’ but the pathway for this to occur is expected to be slow and fraught.
Lintermans, M. (2023). Macquarie perch recruitment monitoring in the upper Murrumbidgee and Mongarlowe rivers: March 2023 results, and five-year project review (2019-2023). Consultancy report to South East Local Land Services. Fish Fondler Pty Ltd
Pavlova et al. (2024). Immediate genetic augmentation and enhanced habitat connectivity are required to secure the future of an iconic endangered freshwater fish population. Evolutionary Applications, 17(10), p.e70019.