Some time ago, we published an article about the fishways at the Koondrook and Cohuna weirs that were constructed in late 2021. More recently, we pondered on the development of performance standards for fishways and what a good fishway looks like. Although still in development, the researchers at Arthur Rylah Institute (ARI) have been collecting data at both the Koondrook and Cohuna fishways to conduct a performance assessment. This data is vital for informing contemporary management and the construction of future fish-friendly infrastructure.

The North Central Catchment Management Authority’s (NCCMA) Native Fish Recovery Plan – Gunbower and Lower Loddon, is a large-scale plan to improve instream flows, habitat, and connectivity. Improving fish passage is a core part of the North Central Catchment Management Authority’s Native Fish Recovery Plan, with the development of each fishway being an action item of the Plan.

A key part of restoring connectivity and passage for native fish was the construction of fishways at the remaining barriers of Koondrook and Cohuna weirs. Through careful design and planning, 140km of Gunbower Creek was reconnected with the Murray River. Native fish which previously pooled at the weirs, are now able to bypass the barriers and access more of the river channel. Post construction, ecological and hydraulic evaluation were required to ensure that the fishways were working to design.

ARI was contracted by the NCCMA in 2021 to undertake a performance assessment (ecological and hydraulic) of the Koondrook and Cohuna fishways and to provide input on the wet commissioning process (trial/testing stage). They conducted fishway trapping, boat electrofishing, and water level and velocity assessments to gather the data required to assess both structures and to help with the wet commissioning. ARI found both fishways are passing fish, but also identified some refinements that could be undertaken. Areas outlined for potential improvement related to:

• modifying fishway attraction flow
• addressing low light levels under the bridge
• reducing build-up of debris and aquatic vegetation

In 2021, the initial trapping results at Koondrook found that both small-bodied and juvenile large bodied native fish were passing through the fishway. These results looked very promising, with Bony bream, Murray-Darling Rainbowfish, Australian smelt, Carp gudgeon and Unspecked hardyhead all utilising the newly installed Koondrook fishway.

However, the recent 2023 studies from both the Koondrook and Cohuna fishways found that large numbers of juvenile carp were passing through, with limited numbers of native fish. To address this issue, adaptive management strategies were utilised informed by the monitoring conducted by ARI. This ultimately led to the fishways being closed. The closure prevented the large accumulations of juvenile Carp from moving into the Gunbower Creek where they would breed, potentially affecting the overall health of the system. Additional sampling at both fishways is recommended following the dissipation of the juvenile Carp, as any additional refinements to the fishway operation will be relevant to native fish.

This work shows the value of ongoing monitoring to allow for adaptive management. In monitoring the fishways in operation, the overall effectiveness of the fishways can be improved to support native fish populations. For more information about fishways and fish movement visit ARI’s website!

Resources

Main Source: ARI Quarterly Update Autumn 2023

NCCMA Native Fish Recovery Plan – Gunbower and Lower Loddon

Koondrook fishways proving to be popular for our native fish

Developing performance standards for fishways

Featured image: Fishway at Cohuna Weir.

Credit: Pam Clunie, ARI

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