Scientists have been out in the field surveying fish across the region’s floodplains.
For the first time, scientists have been able to investigate the movement patterns of juvenile Golden Perch from spawning in the Darling River, through to dispersal and growth in Victorian floodplains. Many of these floodplains offer an excellent nursery habitat for young fish before entering the main river channel.
The project commenced in 2021, funded by Mallee CMA and undertaken by the Arthur Rylah Institute (ARI), ecological monitoring of these juvenile fish commenced, which provides important data for Mallee CMA about the ecosystem’s health and supports the planning of future projects. The recent floods offered the opportunity to capture data during very wet conditions and compare baseline data to dry years. Fish monitoring has been conducted across a vast area from Vinifera Forest, near Swan Hill, to Lindsay Island, near the South Australian border.
Fish surveys recorded 10 native and five introduced species. Excitingly, in late 2021, natural recruitment of Golden Perch was detected in the river, creek, and wetland habitats in the downstream Murray River floodplains. These fish spawned in the Darling River, as confirmed by an analysis of the fish ear bones (called otoliths).
In August 2022, as part of this important survey work, 50 Golden Perch were acoustically tagged, including 25 fish less than a year old. Acoustic loggers were installed throughout Lindsay and Wallpolla Islands to assist with tracking these fish. In addition, 117 large-bodied native fish were also tagged with internal and external tags in autumn this year.
Early results indicate most fish have remained in the same areas, which is surprising considering the extensive flooding of many areas. However, three small fish (approximately 12 months old) moved 70 kilometres upstream, from Crankhandle Lagoon at Lindsay Island into the Murray River and as far upstream as Wentworth.
Interestingly, two Spangled Perch were also recorded at Wallpolla Island in autumn 2023. This species is usually only found in the northern Murray-Darling Basin, but can be found further south, particularly following large flood events.
The findings of this survey work provide important insights into the dispersal and movement of the early life stages of Golden Perch, as well as other fish population dynamics. Monitoring will continue over the next few years and provide invaluable data on the fish populations in the Murray River floodplains.
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This article appeared in The Buloke Times, 27 June 2023.
