Survey finds greater range of water bugs in restored sections of Harvey River

A group wearing waders is visible in the background, standing in knee high water in the Harvey River. A Murdoch University researcher is holding a board with a ruler centred on it up to the camera, and a small fish is lying on the ruler.

Aquatic wildlife monitoring underway in the Harvey River.

Three years of monitoring has recorded a steady increase in the richness and diversity of aquatic macroinvertebrates – also known as water bugs – in restored sections of the channelised lower Harvey River.

Twenty-seven large log structures were installed into the river in 2021, to mimic fallen trees and create pockets of cooler water that enable aquatic life to survive during summer months.

Greening Australia commissioned Murdoch University’s Harry Butler Institute to undertake baseline monitoring and then regular follow-up surveys of the log installation to understand the impact on aquatic wildlife.

“Over the monitoring period (autumn 2021-2023), the richness and diversity of macroinvertebrates increased significantly at the restoration sites compared to the control sites, from 22 species originally to 39 this year. This shows the restored sections are moving things in the right direction,” said Ross Wylie, Senior Program Officer at Greening Australia.

Murdoch University researchers in waders stand in the river channel, among the installed log structures. A net used in aquatic monitoring is visible in the waterway.

Monitoring at the sites where logs were installed found a significant increase in the richness and diversity of macroinvertebrates.

Macroinvertebrates, or water bugs, are animals without backbones that are large enough to see with the naked eye, such as shrimp, snails, and juvenile stages of insects such as dragonflies and damselflies.

The type and number of macroinvertebrates found in a waterway is considered a good indicator of river health.

“Water bugs form that all-important foundation of the food chain for many aquatic wildlife, so seeing this increased richness and diversity at the restoration sites indicates an improvement in conditions and could be a pre-cursor to seeing other aquatic species return in coming years,” said Ross.

The logs installed into the Harvey River are part of a collaborative project between Greening Australia, Harvey River Restoration Taskforce, Department of Water and Environmental Regulation, Water Corporation, scientists, the local community, landholders and Traditional Owners, which aims to recreate a more natural, more climate-resilient watercourse that re-establishes native habitat and brings back aquatic wildlife.

Drone images of this log installation in June 2021 (top photo: just one month after installation) and in November 2022 (bottom photo) show how the log structures are altering the river flow and deeper, cooler refuges are beginning to develop. Photos credit Greening Australia.

Since 2020, more than 15,000 seedlings have also been planted along the riverbanks, to provide longer-term shading effects for the watercourse as they grow.

While the trend for macroinvertebrate species is positive, the final monitoring report showed there hasn’t been a significant change to native fish populations in the restored areas over the study period – this is likely due to variable flows in the channel during the sampling period, and long periods of high water temperatures in summer, which are thought to negatively impact native fish.

“This further emphasises the need to provide cool refuges in waterways to support our native fish populations, particularly in a changing climate. Now that macroinvertebrate populations are increasing, we expect native fish numbers will begin trending in a positive direction as the plants we installed along the streambanks grow taller and help shade the water, and as the in-stream log habitats continue to promote the development of deeper pools in the riverbed,” explained Ross.

Long periods of high water temperatures are thought to negatively impact native fish – making it even more important to provide deeper, cooler refuges in waterways. Photo: Jesse Collins.

The Alcoa Foundation, who funded the project led by Greening Australia, has recently awarded $300,000 to Murdoch University’s Harry Butler Institute for a further three years of monitoring of the restored sections along the lower reaches of the Harvey River.

Ecological monitoring at the restoration and control sites will occur in autumn 2024, 2025 and 2026, providing considerable further insights into how flow and water temperature combine to influence native fish abundance, and whether the restoration that has occurred can moderate those effects.
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