Spotlight on river health: River health assessments get underway as part of Restoring the Serpentine River project

The effects of future management actions will then be monitored by comparing the numbers and different species of native fish and freshwater crayfish, and the condition of vegetation along the foreshore.

This year, the Mandurah Mail has shone a spotlight on the health of the rivers in the Peel region, which continues to decline.

Previous assessments from the 1990s have revealed, of more than 4000 kilometres of waterways throughout the Swan Coastal Plain, only about 1 per cent is in "near pristine condition".

In an effort to uncover why local waterways are not in the condition they should be, the Mandurah Mail will be interviewing environmental experts to gauge the health of local rivers and report on the research being conducted and initiatives in place to help restore them.

After speaking with leaders from the Peel-Harvey Catchment Council (PHCC), who sounded grave concerns about the condition of Mandurah's waterways, the series continues with another significant initiative to help restore the health of the Serpentine River.

Over the past year, the PHCC has partnered with Urbaqua Land and Water Solutions to complete and deliver the Serpentine River Action Plan, aimed at providing insights for future on-ground restoration projects to improve the overall ecosystem and function of the river.

As part of the Action Plan, a team of scientists from Murdoch University have carried out river health assessments at five sites along the Serpentine River to attain a snapshot of the current condition in-stream.

The health assessments are being undertaken as part of the Connecting Corridors and Communities - Restoring the Serpentine River project, to investigate the condition of the lower and middle sections of the river, the bank and foreshore.

Following the River Action Plan's recommended restoration works, future assessments will then be conducted to indicate whether the health of the river is improving, declining or being maintained.

The aim of the River Health Assessments are to provide a report about the current ecological condition to inform the future management of the catchment.

They include both in-stream assessments, made by measuring the number of native fish, freshwater crayfish and macroinvertebrate communities, as well as introduced or exotic species such as goldfish, and vegetation assessments along the foreshore.

Over time, and if repeated with consistency, these assessments can help measure the effectiveness of rehabilitation and management actions on those fish, crayfish and macroinvertebrate communities.

The first River Health Assessments on the Serpentine River, using the South West Index of River Condition (SWIRC) protocols, were undertaken by the PHCC and Department of Water and Environmental Regulation at three sites in 2017.

This was then expanded to include five more sites as part of the River Action Plan, to gain a greater understanding of the current ecological condition of the Serpentine River.

The first assessment of the five sites was undertaken in spring this year, with the second sampling due to occur in autumn 2020 to allow for seasonal changes in aquatic communities as the river becomes more stressed due to reduced flow.

The entire length of the Serpentine River, including the five sites were assessments took place, have significant cultural values.

Local Bindjareb Noongar elders and leaders were consulted in choosing assessment sites and joined in with the field work passing on their intergenerational knowledge and education about the region river.

The completed river health assessments will help to strengthen the Serpentine River Action Plan, which will recommend further locations for additional assessment sites.

To sample the movements and abundance of fish and crayfish, the team used dual-wing fyke nets set approximately 100 metres apart, with fish and crayfish box-style traps set at various positions in between.

Set overnight with one fyke net facing upstream and one downstream at each site, a combination of replicate seine netting and backpack electrofishing was also used to determine densities.

Macroinvertebrates were sampled by sweeping long nets for two minutes in two different locations within the site.

Macroinvertebrate samples were immediately preserved in ethanol before being examined under a dissecting microscope in the laboratory.

Habitat and water quality data was also collected and photographs taken of each location to observe water and vegetation changes.

In addition to the required measurements, additional sampling was undertaken to collect information on the abundance of Carter's freshwater mussels - which were once abundant in the Serpentine River but are now listed as a threatened species in the vulnerable category under the Australian Government's Environmental Protection and Biodiversity Conservation Act.

The only freshwater mussel found in south western Australia, the geographical extent of this species has dropped by 49 per cent in less than 50 years.

Carter's freshwater mussels are important ecosystem engineers, filtering the water to create better environments and conditions for other aquatic life, including freshwater crayfish making them useful as long-term indicators of ecosystem health.

The sampling of mussels will allow comparison with previous assessments of the species to determine its density and population viability.

A technical report will be produced at the end of the assessments, detailing the fish, crayfish and macroinvertebrate populations at each site.

It will also include standardised scores for each of the indicators to summarise the condition of each site and, where relevant, compare this data with the previous surveys conducted in 2017.

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Murdoch University's Dr Stephen Beatty and his team trained PHCC officers, with volunteers carrying out the assessments.

His scientific work extends from the Centre for Sustainable Aquatic Ecosystems to the Harry Butler Institute and he is the research leader for Catchments to Coast.

Dr Beatty said his team at Murdoch were "thrilled" to work with the PHCC and contribute to the River Health Assessments.

"Despite the major modifications since European settlement, our spring surveys revealed it continues to house intact populations of a range of native fish, crayfish and also the South-west Snake Necked Turtle - all of which are only found in the South-West," he said.

"This means restoration efforts will undoubtedly have major, measurable ecological benefits to the Serpentine.

"More importantly, shared learning is the key to building a cohesive plan to restore the Serpentine and other rivers in south west Australia.

"Listening and learning about some of the cultural significance of the river from Uncle Harry, Mark and Tanya on the river was an absolute privilege and definitely the highlight of the week for the research team."

PHCC chair Caroline Knight applauded the team for all their hard work putting the River Health Assessments together as part of the Restoring the Serpentine River project.

"The River Action Plan gives us a good picture of the current condition of the Serpentine River, as well as providing us with a clear road map of priority actions to begin the restoration of the river," she said.

"Assessing the health of the river by investigating what is living below the surface gives us a 'fish-eye view' of the river and provides a good baseline against which we can measure how successful our restoration works have and will be."

In the next installment of the Spotlight on River Health series, we will check back in with the aquaculture project at John Tonkin College to see how students have learnt to grow black bream for release into the Murray River.