Annie Brook Pools

River condition at the Annie Brook Pools site (site code: MB15ANNI1, site reference: 6104073) on Annie Brook 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 Annie Brook Pools 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

Other data:
There are currently no monitored gauging stations on Annie Brook.

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 type was similar between the years, although obviously less abundant under the drier 2022 conditions. The site has poor to moderate structural aquatic habitat complexity, including sparse woody debris of similar sizes. Larger sized woody debris (10–49 cm) was more available in 2017 with the higher water levels inundating these areas of habitat. Woody debris provides aquatic species shelter from terrestrial predators as well as protection from fast flows.

Habitat was also provided by a small proportion of overhanging roots and banks, and by vegetation draped in the water. Draping vegetation provides habitat and food for small fish and macroinvertebrates in addition to its critical role of vegetation in bank stability and shade.

Triglochin, a submerged aquatic macrophyte, also covered a small portion of the assessment site during the spring assessment. Macrophytes provide additional habitat as well as food resources for aquatic fauna, including for species that forage directly on the plant material as well as the associated periphyton and free-swimming invertebrates.

The riverbed consisted of pebble, gravel, sand and silt. In 2017, there was a sparse to moderate cover of organic material (algae and detritus), compared to a dense cover of mostly detritus and leaves in 2022. This is mostly related to the remaining habitat in 2022 being a small river pool, which are deposition sites. The pool was also turbid which restricts algae growth (less light penetration). Organic material provides food for grazers and macroinvertebrates.

Fish and crayfish diversity were similar between the two sampling events. Four native freshwater fish (nightfish, western minnow, western pygmy perch, and freshwater cobbler) and one non-native freshwater fish (eastern gambusia) were present at each sampling occasion. Freshwater crustaceans (smooth marron and gilgie) were present in October 2017 but not detected in March 2022.

In 2017, the native western pygmy perch comprised half of all fish collected, and only a small number of the exotic eastern gambusia were detected (less than five per cent). However, in 2022 eastern gambusia dominated the catch, comprising 63 per cent of all fish.

This cannot be considered a trend as the change in fish community may simply be related to the different sampling periods. That said, eastern gambusia tend to thrive in disturbed or degraded systems because of their relatively high tolerance of habitat and/or water quality changes, and in 2022 dissolved oxygen concentrations were below the minimum guideline value of 4 mg/L (lower range of expected optimal conditions for local freshwater fish species based on Beatty et al. 2013). Low oxygen concentrations (below 4 mg/L) are not uncommon through the latter part of the dry season in many South West rivers, and native fish are able to tolerate these conditions for short periods of time. However, their ability to withstand these situations and compete with invasive species like the eastern gambusia is reliant on their physical condition, and this is a function of ecosystem health (e.g. availability of food, habitat and otherwise good water quality).

Encouragingly, nightfish and western pygmy perch were found in high abundance in 2022 (93 and 83 individuals, respectively). This highlights the importance of refuge areas for native fish during the dry season, with this small pool supporting a relatively large population of native species.

Neither smooth marron nor gilgie were observed during the March 2022 assessment (three and 10 observed, respectively, in 2017). This may be a function of sampling effort (i.e. the species are present but were not detected) and/or the limited aquatic habitat at the site not supporting freshwater crayfish populations (which includes lack of protection from predation by water rats and birds). Future assessments should consider assessing other habitats in the area to assess the status of these species in the system. Note: marron require permanent, good quality water and habitat, which may explain the general absence at this site. Gilgie create burrows for shelter and will retreat to these during the dry season to avoid desiccation; as such, it would not be surprising to see gilgie emerge when water levels increase at 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.

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

• Motorbike frog (Litoria moorei)
• Diving beetle (Family Dytiscidae)
• Water scorpion (Family Nepoidea).

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

References and further 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.

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

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