Upper Vasse

River condition at the Upper Vasse site (site code: VR94VASS1, site reference: 6104084) 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 Upper Vasse site was most recently assessed in March 2022. All known assessments are listed below:

• 2022 – summer (March 14–15): Healthy Rivers
• 2017 – spring (October 11–12): 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 – March)

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 16 km downstream 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.

Aquatic habitat was comparable between the two river health assessments. The site had moderate to good structural aquatic habitat complexity, including dense woody debris in various sizes. Woody debris provides aquatic species shelter from aquatic and terrestrial predators as well as protection from fast flows.

Habitat from vegetation draped in the water covered about half of the assessment site (bank length). Draping vegetation provides habitat for small fish and macroinvertebrates and aids in providing bank stability. Additional habitat was provided by overhanging roots draped in the water, and overhanging banks. Triglochin, a submerged aquatic macrophyte, covered a greater portion of the assessment site in 2017 compared to 2022. This provides additional habitat as well as food resources for aquatic fauna.

The riverbed consisted of cobble, pebble, gravel, sand, silt and clay. Less than half of the substrate had a moderate-density cover of organic material including algae, detritus and leaves, which provides food for grazers and macroinvertebrates.

TRIGLOCHIN AND VEGETATION DRAPED IN WATER PROVIDING AQUATIC HABITAT AT THE UPPER VASSE SITE, OCTOBER 2017

The species captured at the Upper Vasse site during each of the sampling periods are provided in Table 1. The table includes a list of all species previously reported in the subcatchment, which provides an indication of species that may occur at the assessment site. As differences in habitat within a subcatchment naturally influence species distributions, and variability in methods between sampling programs can affect the species caught, this list is only indicative. Below are some of the notable findings from the assessments.

Six species of fish and crustacean were found at this site in October 2017 and March 2022. This includes three native freshwater fish (nightfish, western pygmy perch and western minnow), two native freshwater crayfish (smooth marron and gilgie) and one non-native crayfish (yabby).

Abundance of species between the two sampling events differed, with a greater number of fish found during the March 2022 assessment. This could be because of animals being concentrated in the disconnected pools and, notwithstanding, highlights the importance of this section on the Upper Vasse River as a refuge area during the summer months.

In 2022 a range of size classes including juveniles were recorded for all native fish and crustacean species. Only three individuals of the non-native yabby were found. Some of the western pygmy perch were showing nuptial (breeding) colours. These results demonstrate that this section of the Vasse River can provide suitable habitat and water quality conditions to support successful recruitment for all the native species detected.

In 2022 western pygmy perch and western minnow were the dominant fish species and were recorded in extremely high abundance (1360 and 909, respectively) whereas western pygmy perch was the dominant fish species in October 2017 with 150 individuals recorded.

Smooth marron were the dominant crayfish in March 2022, whereas gilgie were dominant in October 2017. It is not uncommon for these species to inhabit the same environment, though smooth marron are typically restricted to permanent waters whereas gilgie can also tolerate short periods of drying (being able burrow to avoid desiccation). Both species rely on woody debris for shelter and forage on the wood and periphyton (small organisms living on submerged structures).

The mud minnow (listed as vulnerable under the Biodiversity Conservation Act 2016) and salamanderfish (listed as endangered under the Act) were not found in either assessment period. These species were observed in other studies within the wider subcatchment. The salamanderfish was not expected at this specific site as this species is only found in near-coastal wetlands and does not typically occur within riverine habitats. It is not known whether mud minnow inhabits this section of the Vasse River. Mud minnow typically prefer small and gently flowing water bodies.

Note: collection of fauna from inland aquatic ecosystems across Western Australia requires a licence from the Department of Primary Industries and Regional Development and the Department of Biodiversity, Conservation and Attractions. 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 detected:

• Carter’s freshwater mussel (Westralunio carteri) – listed as vulnerable under the Biodiversity Conservation Act 2016
• water birds including Australian white ibis (Threskiornis molucca)
• black rat (Rattus rattus).
• slender water scorpion (Genus: Ranatra)
• diving beetle (Genus: Cybister).

Several dead and alive Carter’s freshwater mussels were observed on the bank upstream of the assessment site. Tracks were visible where mussels were moving from the water’s edge into the water. Mussels can survive outside of water for a short period of time by burrowing into the sediment (Lymbery 2022). Studies have shown that populations of freshwater mussels in the South West have declined over the past decade. Threats to this species include secondary salinisation and drying of habitats (Klunzinger et al. 2015). Freshwater mussels play an important role in freshwater ecosystems as they can maintain water quality by removing sediments and pollutants through filtration (Beatty et al. 2017).

Carter’s freshwater mussel upstream of the Upper Vasse site, March 2022

For more info on these and other aquatic species, please see the River Science fauna page.

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).

Klunzinger MW, Beatty SJ, Morgan DS, Pinder AM and Lymbery AJ (2015). Range decline and conservation status of Westralunio carteri Iredale, 1934 (Bivalvia: Hyriidae) from south-western Australia. Australian Journal of Zoology 63, 127-135.

Lymbery A (2022). They live for a century and clean our rivers – but freshwater mussels are dying in droves. The Conversation.

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

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