Lower Vasse 2

River condition at the Lower Vasse 2 site (site code: VR64VASS2, site reference: 6104083) on the Vasse River has been assessed as part of the Healthy Rivers program using standard methods from the South West Index of River Condition (SWIRC). The SWIRC incorporates field and desktop data from the site and from the broader catchment. Field data collected include the following indicators, assessed over about a 100 m length of stream:

• Aquatic biota: fish and crayfish community information (abundance of native and exotic species across size classes, general reproductive and physical condition)
• Water quality: dissolved oxygen, temperature, specific conductivity, and pH (logged in situ over 24 hours), as well as laboratory samples for colour, alkalinity, turbidity and nutrients
• Aquatic habitat: e.g. water depth, substrate type, presence of woody debris and detritus, type and cover of macrophytes and draping vegetation
• Physical form: channel morphology, bank slope and shape, bioconnectivity (barriers to migration of aquatic species), erosion and sedimentation
• Fringing zone: width and length of vegetation cover within the river corridor and lands immediately adjacent, structural intactness of riparian and streamside vegetation
• Hydrology: measures of flow (velocity) at representative locations (compared against data from stream gauging stations within the system)
• Local land use: descriptions of local land use types and activities (compared against land use mapping information for the catchment)

The Vasse River 2 site was most recently assessed in March 2022. All known assessments are listed below:

• 2022 – summer (March 14–15): Healthy Rivers
• 2017 – spring (October 9–10): Healthy Rivers

For a subset of the assessments above, water quality loggers were deployed for extended periods (see below). This enabled assessment of water quality responses to changes in climate, streamflow, and factors such as the intactness of vegetation within the river corridor. Amongst other things, this allows detection of sub-optimal water quality conditions which can be missed during the standard 24-hour assessment.

• 2017‒18 summer (October to February)

Other data:
There are currently no monitored gauging stations on the Vasse River. However, the Vasse River – Outlet Diversion Drain gauging station (site reference: 610045), about 3.3 km upstream of the assessment site, was in operation from 2014 through to 2020. The gauging station is owned by Water Corporation.

Search the site code or site reference in the Department of Water and Environmental Regulation’s (the department) Water Information Reporting (WIR) system to find data for this site and nearby sampling points (flows, surface water quality, groundwater monitoring, department’s meteorological data). See also the Bureau of Meteorology website for additional meteorological data for the area.

Note: two fyke nets deployed upstream of the Busselton Bypass Bridge were stolen during the March 2022 assessment. The data provided is based on a single fyke net deployed downstream of the bridge; therefore, results may not be wholly representative of the site.

Five species of fish and crustacean were found in March 2022. These were one native freshwater fish (western pygmy perch), two native freshwater-estuarine species (blue-spot goby and sea mullet), one native freshwater crustacean (south-west glass shrimp) and one non-native fish species (eastern gambusia).

Eastern gambusia and the south-western snake-necked turtle (listed below in ‘Other aquatic fauna’) dominated the catch. These species are both highly tolerant to poor water quality, suggesting this section of the river is under stress. Dissolved oxygen concentrations and pH was elevated during the 24-hour site assessment, which is as expected given the observed algal bloom. Nutrient concentrations (total phosphorus and total nitrogen) also exceeded ANZECC/ARMCANZ 2000 guidelines, which explains the increased algal productivity and reflects the known eutrophication issue for the catchment.

More information on water quality and current management plans for the Lower Vasse River can be found via Revitalising Geographe Waterways.

The black-stripe minnow has been found in coastal wetland habitats within the wider subcatchment (Morgan & Beatty 2006). This species is not expected at this specific site as they do not typically occur within riverine habitats.

Non-native goldfish are known to exist in the subcatchment (refer to reference section) but were not observed in October 2017 and March 2022. Whilst it is unlikely they have disappeared from the system (being highly tolerant), this is a good indication that they are not present in significant numbers. Goldfish population control studies have taken place by Murdoch University in the Vasse River since 2003. Published papers can be found in the ‘References and further reading’ section below. Goldfish can be a significant threat to the Vasse River as they:

• potentially encourage the growth of cyanobacteria as cells become activated as they pass through the digestive tract (Kolmakov and Gladyshev 2003; Morgan & Beatty 2007)
• increase turbidity and resuspend nutrients available for algal uptake because of vigorous benthic foraging methods
• compete for food and habitat with native fish, as well as predate on their eggs (Morgan & Beatty 2007).

Note: collection of fauna from inland aquatic ecosystems across Western Australia requires a licence from the Department of Primary Industries and Regional Development (DPIRD) and the Department of Biodiversity, Conservation and Attractions (DBCA). All species collected must be reported to these agencies as part of licence conditions.

Although not directly targeted as part of the Healthy Rivers assessment, the following species were recorded:

• Carter’s freshwater mussel (Westralunio carteri) – listed as vulnerable under the Biodiversity Conservation Act 2016
• south-western snake-necked turtle (Chelodina oblonga) – about 35 individuals recorded.

Given high turbidity (low visibility) and potentially toxic algal bloom, a quantitative mussel assessment was not carried out; however, a single Carter’s freshwater mussel was observed on the bank (alive) downstream of the bridge. This species plays an important role in freshwater ecosystems as they can improve water quality by removing sediments and pollutants through filtration (Beatty et al. 2017). More information on Carter’s freshwater mussels in the lower Vasse River can be found in the references provided.

Carter’s freshwater mussel at Lower Vasse 2, March 2022

References and further reading:

Beatty SJ, Ma L, Morgan DL and Lymbery A (2017). Baseline assessment of Carter’s Freshwater Mussel, Westralunio carteri at proposed bridge construction sites on the Lower Vasse River. Centre for Fish and Fisheries Research Group and Fish Health Unit (Murdoch University).

Morgan DL & Beatty SJ (2007). Feral Goldfish (Carassius auratus) in Western Australia: a case study from the Vasse River. Journal of the Royal Society of Western Australia. 90: 151–156.

Morgan DL & Beatty SJ (2006). Overview of the feral Goldfish Control Programme in the Vase River, Western Australia: 2004–2006. Centre for Fish and Fisheries Research Group and Fish Health Unit (Murdoch University) report to Geocatch.

Paice R & Beatty SJ (2021) Survey of Carter’s Freshwater Mussel in the Lower Vasse River to inform future sediment removal. Centre for Sustainable Aquatic Ecosystems Harry Butler Institute (Murdoch University) & Ottelia Ecology.

Revitalising Geographe Waterways – RGW (dwer.wa.gov.au)

Vasse Taskforce – RGW (dwer.wa.gov.au)