Collie River - Downstream Rose Road Gauging Station

River condition at the Downstream Rose Road Gauging Station site (site code: CR131COLL2, site reference: 6124038) on the Collie 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 Downstream Rose Road Gauging Station site was most recently assessed in March 2023. All known assessments are listed below in Table 1:

Other data:
The Downstream Rose Road Gauging Station site is about 200 m downstream of the Rose Rd Gauging Station (site reference: 612043) on the Collie River. The gauging station is owned by the Department of Water and Environmental Regulation (the department) and has been in operation since 1996.

Search on 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.

The site had a moderate complexity of aquatic habitat (compared to what would be expected naturally), characterised by a moderate cover of wood in two to three different size categories. Smaller sticks/twigs were absent though larger pieces of wood remained. Woody debris, particularly large logs, provides aquatic species shelter from aquatic and terrestrial predators (physical and psychological), and refuge in fast flows, as well as substrate for growth of periphyton (algae and invertebrates), which are also an important part of the food web.

Only a small proportion of the banks had vegetation that draped in the water, which is reflective of a reduced riparian zone. There was a high proportion of overhanging and draping tree roots and overhanging banks, which reflects the degraded fringing zone (erosion) but also provides some aquatic habitat.

The riverbed consisted of bedrock, gravel, sand, silt, and clay. This provides habitat for invertebrates which are critical for ecosystem processes (such as nutrient cycling) and form an integral part of the diet of many native fish and crayfish species. About half of the site was covered in organic material including epiphytes, algae, detritus and leaves. Organic material provides further food for grazers and macroinvertebrates.

Water quality measured over the 24-hour collection period (29–30 March 2023) was within moderate to optimal conditions for South West rivers based on the known tolerances of fish and crayfish.

Dissolved oxygen remained above the lower limit of 4 mg/L used in the SWIRC and had a diurnal range of 2.8 mg/L. Concentrations below 4 mg/L can be directly stressful to fish and crayfish and can affect basic ecological processes (such as nutrient cycling).

The mean water temperature was 19.2°C with a diurnal range of 2.9°C. This is within optimal ranges expected for South West streams (SWIRC guidelines), based on the recommended upper range for temperature of 25°C and within a diurnal range of 4°C. Figure 1 shows the relationship between dissolved oxygen and temperature at the assessment site over the 24-hour sampling period.

FIGURE 1: DISSOLVED OXYGEN AND WATER TEMPERATURE RELATIONSHIP AT THE DOWNSTREAM ROSE ROAD GAUGING STATION SITE, MARCH 2023

Dissolved oxygen saturation concentrations were slightly elevated over typical conditions, which indicated increased algal activity. This was supported by field observations of algae covering the physical substrate including the riverbed, and a low density of algae in the water column.

The mean salinity at this assessment site was 1450 mg/L. This is within the marginal brackish salinity category and is elevated based on natural expectations for this system. Many of the south-west native freshwater fish species appear to be able to tolerate these levels, being found in waters ranging between 500 to 2500 mg/L (Mayer et al 2005); however, smaller invertebrates and aquatic plants and algae would be under stress.

The species captured at the Downstream Rose Road Gauging Station 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.

Ten species of fish and crustaceans were found at this site in the March 2023 assessment. These were four native freshwater fish (nightfish, western pygmy perch, western minnow, and freshwater cobbler), two native estuarine-freshwater fish species (south-western goby and sea mullet), three native freshwater crustaceans (smooth marron, gilgie and south-west glass shrimp) and one non-native freshwater fish (eastern gambusia).

Freshwater cobbler, the largest native freshwater fish species in the South West, was the dominant fish species at the site. This species prefers deeper water with large woody debris and undercut banks. The population incorporated a range of size classes with juveniles (0‒100 mm) comprising about one-third of the catch and some individuals exceeding the typical maximum adult length of about 400 mm (total length). The longest cobbler captured was 630 mm which to our knowledge is the largest ever reported in natural river systems. This demonstrates that this section of the Collie River provides suitable habitat to support recruitment of freshwater cobbler.

Whilst the site had a diverse range of small-bodied freshwater fish and crayfish, abundances were low. This was also consistent across the previous sampling events. Low abundance, but high richness, is often related to quantity of habitat. This result could be attributed to the previously identified degradation of the riparian zone, which includes both a reduced ground layer (rushes and sedges) and absence of shrubs (such as tea tree). An intact riparian zone provides an important source of structure for in-stream habitat (from draping and dropped vegetation) and provides shading and bank stability. Bank erosion at the site and further upstream has also resulted in sedimentation. Deposited sediments fill in the spaces around logs and larger substrates, further diminishing habitat availability

Blue-spot goby were absent from the March 2023 assessment but had been present in the previous assessments. This is not a concern as the blue-spot goby is an estuarine-freshwater fish species and is known to move between the two environments.

The exotic eastern gambusia was also present, but in low abundances. Native fish have been shown to successfully compete with gambusia when the natural environment is in good condition, whereas gambusia gain a competitive advantage in disturbed systems given higher tolerances for water quality and habitat changes.

Two species of crayfish were recorded at this site. It is not uncommon for more than one species of crayfish to coexist in the same environment. Smooth marron typically relies on permanent waters, whereas gilgies can tolerate seasonal drying by digging burrows to the water table to avoid desiccation.

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.

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 AT THE DOWNSTREAM ROSE ROAD GAUGING STATION SITE, MARCH 2023

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).

Mayer XM, Ruprecht JK and Bari MA 2005, Stream salinity status and trends in south-west Western Australia, Department of Environment, Salinity and Land Use Impact Series, Report No. SLUI 38.