Fish are good indicators of the ecological health of river systems. They are readily identifiable, and occupy a wide range of habitats longitudinally, from alpine to estuarine waterways, and laterally, from river channels to floodplain wetlands. Fish species occupy multiple trophic levels, ranging from algaevores/detritivores to apex predators. Many species are long-lived and their populations can integrate ‘river health’ effects over multi-decadal timescales. Many species of native fish show dispersal or movement behaviours and, for some, these behaviours are probably critical to long-term population health.
Some of the key threats to fish dispersal are flow related — directly to either the quantity or quality of the flow, or indirectly via effects of the infrastructure built to regulate flows for human use. Research on the performance and significance of fish dispersal behaviours is critical to evaluate whether river operations (flows and infrastructure) are performing in such a way as to promote healthy fish populations.
The Sea to Hume fishway construction program was a $77M program that spanned ten years — the biggest fish passage rehabilitation program ever undertaken in Australia. As such, it formed an essential component of the Murray–Darling Basin Authority Native Fish Strategy, a large, long-term river restoration project that was enthusiastically supported by The Commonwealth and State Governments of South Australia, Victoria, NSW and Queensland; and was extremely popular with community stakeholders in all jurisdictions.
The Sea to Hume program included the installation of automated Passive Integrated Transponder (PIT) technology to monitor the movements of migratory fish both during and beyond the construction program. This monitoring infrastructure is an essential tool to report on, and potentially fine-tune, the effectiveness of the program in meeting its original ecological objectives — i.e. that of rehabilitation of fish-passage and native fish communities throughout the Murray–Darling Basin.
To be truly effective, the program requires a population of tagged fish being present within the river. Naturally occurring population processes dictate that the tagged fish population slowly turns-over through time. Over 40 000 tagged fish were liberated into the Murray River over the past decade, mainly by the ‘Tri-state Murray River Fishway Assessment Program’ (MRFAP). However, due to natural attrition, and major blackwater events, it is expected that this number of tagged fish would now be severely depleted.
There is a pressing need to increase tagged fish numbers to ensure that the automated-system can optimally record fish movements. Murray–Darling Basin Authority analysis has shown that tagging by lock-staff will be much more cost-effective than Tri-state Murray River Fishway Assessment Program (MRFAP) after including training costs (MDBA 2016, ‘Pilot Program Proposal — Fish Tagging at River Murray fishway sites’). Staff at the Centre for Freshwater Ecosystems La Trobe Mildura are highly experienced in fish tagging and fish handling techniques, and are well-placed geographically (Mildura) to cost-effectively train lock-staff with necessary skills.
The objectives of this research theme are to:
- Develop a program for training lock staff to enable tagging of fish at up to three sites initially at Lock 10, Lock 7 (or 8 or 9) and Lock 15.
- Develop appropriate methodologies for the ecological-interpretation and analysis of the existing and developing fish-movement dataset.
- Generate and answer key ecological questions relating to fish movement, fishways and river rehabilitation in the southern connected system.
- Provide ongoing insight into appropriate ways to manage flows and fishways to achieve the overarching rehabilitation objectives of the Sea to Hume and Native Fish Strategy programs to the benefit of all Murray–Darling Basin States.
- Develop a plan for the broader roll-out of fish tagging by lock staff at other sites along the Murray River.
Develop a program for training lock staff to enable tagging of fish at up to three sites initially at Lock 10, Lock 7 (or 8 or 9) and Lock 15.
The Centre for Freshwater Ecosystems will lead a collaborative process with the Murray–Dar ling Basin Authority, Authur Rylah Institute (ARI), Fisheries NSW, the South Australian Research and Development Institute Aquatic Sciences (SARDI), Charles Sturt University (CSU) and the State constructing authorities to:
- develop appropriate methodologies for the ecological-interpretation and analysis of the existing and developing fish-movement dataset
- generate and answer key ecological questions relating to fish movement, fishways and river rehabilitation in the southern connected system
- provide ongoing insight into appropriate ways to manage flows and fishways to achieve the overarching rehabilitation objectives of the Sea to Hume and Native Fish Strategy programs to the benefit of all Murray–Darling Basin States
- develop a plan for broader roll-out of fish tagging by lock staff at other sites along the Murray River.
- Protect and restore water-dependent ecosystems
By building the capacity to tag fish through the training of Lock staff thereby increasing the number of tagged fish in the system, and analysis of existing data on fish-passage, this project will provide water resource managers with knowledge on how to effectively manage flows to promote the movement of fish along the length of the Murray River and create lateral connectivity.