Sabina River 1

River condition at the Sabina River site (site code: VR60SABI1, site reference: 6104080) on the Sabina 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 Sabina River site was most recently assessed in March 2022. All known assessments are listed below:

• 2022 – summer (March 16–17): 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 Sabina River. However, the Sabina Diversion – Wonnerup East Road gauging station (site reference: 610025) is about 6.5 km upstream of the assessment site on Sabina River main drain. This gauging station is owned by the Department of Water and Environmental Regulation (the department) and has been in operation since July 2000.

Search the site code or site reference in the department’s 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 not comparable between the two river health assessments as this section of the Sabina River was dry in March 2022 compared to the spring assessment in October 2017.

In 2017 the site had moderate structural aquatic habitat complexity, including sparse woody debris in two to three different sizes (<5–49 cm). Woody debris provides aquatic species shelter from aquatic and terrestrial predators as well as protection from fast flows.

During the spring assessment, habitat from vegetation (mostly grass) draped in the water covered more than half of the assessment site (bank length). Draping vegetation provides habitat for small fish and macroinvertebrates and aids in providing bank stability. Though grass draped in the water can provide shelter, it provides limited shelter compared to rushes, sedges, and shrubs, particularly when water levels rise and fall with flows. Additional habitat was provided by a small percentage of overhanging roots draped in the water.

The riverbed consisted of bedrock, boulders, cobble, pebble, gravel, sand, silt, and clay throughout the channel. The substrate had a moderate cover of organic material including algae, detritus, and leaves, which provides food for grazers and macroinvertebrates.

The species captured at the Sabina River site during each of the sampling periods are provided in Table 2. 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.

Three species of fish were found at this site in March 2022, compared to five species of freshwater fish and two species of freshwater crustaceans in 2017. These were one native freshwater fish (western minnow), one native freshwater-estuarine species (blue-spot goby) and one non-native fish species (eastern gambusia).

Eastern gambusia (juveniles and adults) dominated the catch in March 2022, whereas blue-spot goby were the dominant species in October 2017. Eastern gambusia only comprised a small percentage (less than ten per cent) of the catch in October 2017. Native fish have been shown to successfully coexist and outcompete eastern gambusia in natural environments (i.e. good water quality and preferred aquatic habitat). Eastern gambusia tend to thrive in disturbed or degraded systems given high tolerance to poor water quality including low dissolved oxygen concentrations.

The native nightfish, western pygmy perch, gilgie and freshwater shrimp were recorded in October 2017 but not in 2022. Their absence can be attributed to the naturally drier conditions at this time of year; however, further assessment is needed to ensure they continue to be supported under the altered flow conditions.

During dry periods, native freshwater fish species migrate to permanent summer refuge pools, and the native gilgie can burrow into the water table to avoid desiccation. A pool was found about 2.5 km downstream of the assessment site on the Sabina River which appeared to be a refuge area for freshwater fish during the dry period. The native nightfish, blue-spot goby, south-western snaked-neck turtle, and freshwater glass shrimp, as well as the non-native eastern gambusia, were found in this pool. More information on this site (Sabina River 3) can be found here.

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:

• A froglet (thought to be a bleating froglet, Crinia pseudoinsignifera) was recorded. This froglet species is endemic to Western Australia.
• Motorbike frog.

Froglet at Sabina River, March 2022

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

References and further reading:

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

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