Short-term intervention monitoring of a fish community response to an environmental flow in the mid and lower Macquarie River: 2014-15 watering year

About the document

Between 5 October and 12 December 2014 around 28,500 ML of Commonwealth and NSW environmental water was released from Burrendong Dam to flow down the Macquarie River to provide access to suitable fish habitat, promote fish movement and provide cues for spawning, recruitment and migration of native fish. These environmental flows provided water to the inner floodplain vegetation of the Macquarie Marshes and supported native fish in the Macquarie River.

Monitoring has shown that the environmental outcomes of this watering included increased hydrological connectivity of the Macquarie catchment, the spawning of eight species of native fish and the successful recruitment of native fish including the iconic Murray cod, eel-tailed catfish, Australian smelt, un-specked hardyhead and Murray–Darling rainbowfish.

The environmental outcomes of these flows were enhanced by the work of the NSW Government in addressing the impacts on fish caused by cold water pollution from the Burrendong Dam. In 2014, a cold water pollution curtain was installed at the Dam. This curtain, along with environmental flows, achieved one of the 2014‑15 Basin Annual Environmental Watering Priorities -Improve native fish habitat within the Macquarie River below Burrendong Dam by restoring a more natural flow regime and managing cold water pollution.

The Commonwealth Environmental Water Office contracted the NSW Department of Primary Industries Fisheries to undertake a short-term monitoring project to assess the response of native fish in the Macquarie River to these environmental flows.

The key observations of this monitoring included:

• The environmental flows increased the hydrological connectivity, and in combination with appropriate water temperatures (as a result of the timing of the flow and the cold water pollution mitigation curtain at Burrendong Dam), supported recruitment of Murray cod¹ and the eel-tailed catfish² which are listed as key species in the Basin Wide Environmental Watering Strategy.
• Sampling captured 18 species of fish (12 natives, four exotic and two native decapods).
•  Nine species of fish spawned (eight natives and one exotic) – Australian smelt, carp cudgeon, Murray cod, un-speckled hardyhead, flathead gudgeon, eel-tailed catfish, Murray-darling rainbow fish, bony bream and common carp. Some of this spawning is likely to be a response to the increase in water temperature.
• Peaks in recruitment of Murray cod, eel-tailed catfish, Australian smelt, un-specked hardyhead and Murray–Darling rainbowfish occurred during the environmental water release. The increased flow may have increased food availability and facilitated successful recruitment.
• As expected, sampling did not show any spawning or recruitment of golden or silver perch as these species require higher flows to spawn.
• The monitoring provided additional information on spawning thresholds for bony bream which will inform future environmental water delivery.
• Flows from the Barwon River in July 2014 may have allowed bony bream to move from the Barwon River to the Macquarie River.
• The benefits for fish in the Macquarie River from the cold water curtain and environmental flows should continue to be seen over time.

This fish monitoring provides valuable information on how fish respond to flows in the Macquarie and will help inform future environmental watering and management decisions in the Macquarie catchment.

¹ Listed as Vulnerable under the Environment Protection and Biodiversity Conservation Act 1999

² Listed as Endangered under the NSW Fisheries Management Act 1994