Station Gully

River condition at the Station Gully site (site code: MB16STAT1, site reference: 6104081) on Station Gully 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 Station Gully site was first assessed under Healthy Rivers in October 2017 and most recently in December 2024. The site was not assessed in March 2022 as part of routine assessments across the Busselton Coast region as the site was dry. All known assessments are listed in Table 1 below:

Other data:
There are currently no monitored gauging stations on Station Gully.

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 consistent between the two assessments.

The site had poor to moderate structural aquatic habitat complexity, largely related to historical clearing/grazing of the riparian zone.

In-stream habitat included a moderate abundance of woody debris in a variety of sizes. This provided some shelter for small and large-bodied fish from fast flows as well as protection from aquatic and terrestrial predators.

A small percentage of the site had habitat provided by aquatic macrophytes (submerged and floating) and riparian vegetation (such as rushes) draped in the water.  In addition to structural habitat for small fish and macroinvertebrates, the aquatic and submerged vegetation provided a source of food, with fauna able to feed directly on the vegetation or on the periphyton (bacteria and algae) that grow on the surface of roots and leaves.

The reduced riparian zone also impacted bank stability, evident through a high severity of erosion and sand sedimentation throughout the site, as well as providing little capture or processing of organic material and nutrients in runoff from the catchment.

The stream substrate had a sparse cover of organic material including algae, detritus and leaves, which provides food for aquatic fauna.

Water quality measured over the 24-hr collection period (4–5 December 2024) was within optimal conditions for southwest species, with the exception of the diurnal temperature range (over a 24-hour cycle). Refer to footnotes below for guideline values.

Dissolved oxygen was above the lower limit of 4 mg/L and had a diurnal range of 2 mg/L.

The mean water temperature was 19.6°C which is optimal, however the diurnal range of 8°C exceeded the recommended range of 4°C. The diurnal variability of water temperature could be due to a few factors including a reduced riparian zone and variability in water depths throughout the site. Shallow water is more susceptible to changes in ambient temperatures as thermal regulation is more difficult.

Figure 1 shows the relationship between dissolved oxygen and temperature at the assessment site over the 24-hour sampling period.

Footnote:

¹ A lower limit of 4 mg/L is taken from the SWIRC where it is used as a guideline limit for condition scoring. This level aligns with Beatty et al. (2013) where south-west native fish species were shown to typically reside in sites with levels above 4 mg/L.

² An upper limit for temperature is nominally set at 25°C based on the range recorded in sites where south-west native fish species are typically found to occur (Beatty et al. 2013).

The mean salinity was within the fresh salinity category during both assessments.

Nutrients (total nitrogen, 0.45 mg/L and total phosphorus, 0.018 mg/L) are considered to be indicative of low disturbance based on the SWIRC categories. The SWIRC categories are based on analysis of departure from natural local conditions across a range of sites across south-west WA within difference land use settings.

Station Gully lies within the Annie Brook catchment. The primary land use within the catchment is beef grazing, with pockets of horticulture, viticulture, timber plantations, rural residential (predominantly in the mid and lower catchment) and State Forest (Yelverton National Park) in the upper catchment. Please visit the Annie Brook – Revitalising Geographe Waterways website for more information on water quality and nutrients for this catchment.

The species captured at the Station Gully 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.

Six species of fish and one crayfish were found at this site in December 2024. These were:

• three native freshwater fish: nightfish, western pygmy perch and western minnow
• two native freshwater crayfish: gilgie and smooth marron
• one non-native fish: eastern gambusia.

Western minnow was the dominant fish species in December 2024, whereas western pygmy perch was the dominant fish species in October 2017. In October 2017 some of the western pygmy perch were showing signs of nuptial (breeding) colours but there was no evidence of recruitment. There was evidence of recruitment in the December 2024 assessment as more than half of the observed western pygmy perch were juveniles (between 0–20mm).

Eastern gambusia have been found in low abundance during both assessments. Native fish have been shown to successfully coexist and outcompete eastern gambusia in natural environments (i.e. good water quality and preferred aquatic habitat).

Gilgies comprised a third of the catch during both of the assessments, with a range of size classes present including juveniles. The ability for gilgie to burrow to maintain contact with the water table during dry periods explains their dominance at the site, with the site drying in 2022.

Smooth marron were observed at the site for the first time in December 2024, with this species generally only found in areas of permanent surface water. The presence of smooth marron, which are not expected to move rapidly to avoid drying, suggests a permanent-water dry-season refuge exists very close to the site.

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.

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

References and recommended reading

Beatty S, Morgan D, Keleher J, Lymbery A, Close P, Speldewinde P, Storer T & Kitsios A 2013, Adapting to climate change: A risk assessment and decision-making framework for managing groundwater dependent ecosystems with declining water levels. Supporting document 4: Environmental variables in the habitats of southwestern Australian freshwater fishes: An approach for setting threshold indicator value, National Climate Change Adaptation Research Facility, Gold Coast.

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.

Revitalising Geographe Waterways – RGW (https://rgw.dwer.wa.gov.au)

Vasse Taskforce – RGW (https://rgw.dwer.wa.gov.au/about-vasse-taskforce/)