Capel River - Capel River 1

River condition at the Capel River 1 site (site code: CR50CAPE1, site reference: 6100287 ‒ previously reported as site code: CAPE-01, site reference: 6100090) on Capel 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 Capel River 1 site was most recently assessed in March 2022. All known assessments are listed in Table 1 below:

It should be noted that considerable effort is underway to improve health in the system and wider catchment under the Revitalising Geographe Waterways program, run by the multi-agency Vasse Taskforce.

Other data:
The Capel River - Huttons Gauging Station (site reference: 610061) is located at the Capel River 1 site. The gauging station is owned by the Department of Water and Environmental Regulation (the department) and has been in operation since 2012.

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.

The site had moderate to good structural aquatic habitat complexity, including dense woody debris of various sizes throughout the site. Woody debris provides aquatic species shelter from fast flows as well as protection from aquatic and terrestrial predators.

Additional habitat was provided by a small number of overhanging roots draped in the water and overhanging banks. Less than half of the assessment site had vegetation (mostly grass) draped in the water. The lack of vegetation draped in the water is reflective of a reduced ground and shrub layer within the riparian zone. Vegetation draped in the water can provide habitat for small fish and macroinvertebrates and can aid in providing bank stability. Though grass draped in the water can provide shelter, this shelter is limited compared to that of rushes, sedges and shrubs, particularly when water levels rise and fall with flows.

The riverbed consisted mostly of gravel, sand and silt throughout the channel, and boulders and cobble at the riffle under the bridge. The substrate had a moderate cover of organic material including algae, detritus, epiphytes and leaves, which provides food for grazers and macroinvertebrates.

The species captured at the Capel River 1 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.

Fish and crayfish assemblages have varied between the five sampling events.

Western minnow, freshwater cobbler, gilgie and smooth marron have been present at each sampling occasion.

In 2009 and 2020, freshwater cobbler were the most dominant species in the catch. Cobbler are the largest native freshwater fish species in the South West and prefer deeper water with complex habitat (large woody debris and undercut banks). Though a range of size classes were present at each of the sampling events, the catch was mostly made up of larger sized fish (no juveniles were present during the 2020 and 2022 sampling events). This species is known to undertake localised migrations, moving upstream during the wetter months to access spawning and nursery grounds, which can explain variations in catches at different times.

The exotic redfin perch was the most abundant species during the 2016 and 2019 assessments. All individuals (73) collected in 2019 were juveniles (less than 10 cm), and all individuals (44) in 2016 were slightly larger, measuring 10‒20 cm in length. Redfin perch grow to about 40 cm in local waters and are considered one of the most significant predators of native fish and crayfish species. It should be noted that redfin perch were not recorded in 2020 and numbers were low in 2022.

The pouched lamprey was recorded at the 2009 sampling event with 11 ammocetes (larvae) caught in traps and nets. An adult lamprey was also observed in 2016 upstream at the Yates Bridge site. The pouched lamprey is a Priority 3 species (poorly known) under the Biodiversity Conservation Act 2016 (WA). Priority 3 refers to possibly threatened species with insufficient data to assess threatening processes that could affect them. This species is not expected to be under imminent threat based on available data. In the early stage of their life cycle, lamprey burrow in sand in upper reaches of river systems. They migrate to the ocean where they may remain and feed for several years. Eventually lamprey will migrate back up river systems to spawn and die. Outside of the short migration periods, lamprey are unlikely to enter traps. The absence of lamprey from most SWIRC assessments is not a significant concern as this species typically migrates in a brief period around peak winter flow (which is largely outside of the usual assessment periods) and only in high-flow years.

In 2020, sampling was conducted by Murdoch University on the behalf of the department to investigate fish assemblages within the wider Whicher Allocation Plan Area (between Capel and Blackwood Rivers). This work was undertaken in the wet season in response to the absence and low numbers of some species at several sites monitored through the routine Healthy Rivers program assessments. One of the concerns for the Capel River 1 site was that western pygmy perch have not been present (known to occur elsewhere in the system, including in low abundance at a site upstream) and that nightfish have only been recorded in low numbers, with a lack of juveniles. A single nightfish, which was within the larger size category (110 mm), was recorded at the assessment site in 2016. Both these species are common and highly catchable (i.e. if they are present, they are expected to be detected). The 2020 and 2022 sampling events failed to find either of these species. As other native species still occur and appear to be healthy, this is likely more a function of predation pressure from redfin perch combined with habitat availability (in-stream structure such as the lack of vegetation draped in water and connectivity) than water quality. Further assessments at more sites in the reach are recommended to better understand species distribution and needs.

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 Carter’s freshwater mussel (Westralunio carteri) was also found. This species is listed as vulnerable under the Biodiversity Conservation Act 2016.

Carter’s freshwater mussels were observed in the water and on the bank at the Capel River 1 assessment site in February 2019 and March 2022. This species plays an important role in freshwater ecosystems as they are able to maintain water quality by removing sediments and pollutants through filtration (Beatty et al. 2017).

Carter’s freshwater mussel at Capel River 1, 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).

Beatty, SJ and Morgan DL (2020) Status of aquatic fauna in systems on the Whicher Scarp: Summary report. Harry Butler Institute. Centre for Sustainable Aquatic Ecosystems. Prepared for the Department of Water and Environmental Regulation.

Storer, T, White, G, Galvin, L, O’Neill K, van Looij, E & Kitsios, A 2011, The Framework for the Assessment of River and Wetland Health (FARWH) for flowing rivers of south-west Western Australia: project summary and results, Final report, Water Science Technical Series, report no. 39, Department of Water, Western Australia.

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

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