Our 92-hectare Watchalunga Nature Reserve, nestled in the Lower Finniss region of South Australia, provides diverse habitats for a myriad of native animals, including freshwater fish. The Lower Finniss, a vital region for freshwater fish, serves as an extensive wetland habitat and hydrological connector between the upstream habitat and the Lower Lakes and Murray Mouth.
Since 2018, we've been conducting targeted annual fish surveys to monitor the fish community's status and provide a temporal and spatial comparison of fish abundance within Watchalunga Nature Reserve. The recent 2024 spring survey, conducted by Nature Glenelg Trust for our Science and Knowledge team with the support of Nature Foundation volunteers, revealed some intriguing and promising results following the 2022/2023 floods.
Following identification, observation and measurement, the survey team returned native fish to the water at the point of capture; alien fish were removed and euthanised. All fish sampled appeared in good health with no obvious deformities, disease, or parasite infestations apparent. In addition to fish records, environmental descriptors, such as the extent of habitat cover, flow and pool condition, and water quality parameters, were also recorded to aid the interpretation of results and assist with a broader condition assessment.
The survey recorded 1077 fish across 15 species, with 92% of the catch being native species. We were pleased to observe a rise in native fish species, with 10 of the 15 species sampled being native fish, two more than in 2023 and one more than in 2022 and 2021. Overall, the total fish catch in 2024 was the highest since fish monitoring commenced in 2018.
The native and diadromous species Common Galaxia (Galaxius maculatus) was the most abundant species caught during the survey, accounting for 41.6% of the total catch. The native freshwater generalist Flathead Gudgeon (Philypnodon grandiceps) was the second most abundant species, representing 36.4% of the total catch. These species were recorded in significantly higher quantities in both cases than in the previous years' surveys. The estuarine Lagoon Goby (Tasmanogobius lasti) was also detected for the first time, though in meagre numbers.
The five alien species combined contributed to 8.3% of the total catch, a significant decrease compared to 2023, when it dominated 74.8% of the total catch. The Common Carp (Cyprinus carpio) was the most abundant alien species caught, followed by the newly detected Oriental Weatherloach (Misgurnus anguillicaudatus). Redfin Perch (Perca fluviatilis) was also recorded, though in lower numbers than previous years.
The increased abundance of native fish is likely due to increased connection across the river and wetlands system following the 2022/2023 floods, along with the 2022 and 2023 electrofishing exercises, which have greatly decreased the abundance of the alien fish community.
We are eager to continue regular electrofishing and undertake other activities to restore aquatic habitat, support the resident fish community, and encourage the recolonisation of key threatened freshwater fishes. We are seeking funding to assist with these efforts.
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Photo by Sylvia Zukowski, Nature Glenelg Trust.