Walpole River - Plain Road Upstream

River condition at the Plain Road Upstream site (site code: DR17WALP1, site reference: 6064005) on the Walpole River has been assessed as part of the Healthy Rivers Program (Healthy Rivers), 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 around 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)

This is the first assessment of this site using the SWIRC methods. At this time no previous assessments of river ecology had been reported.

Assessments are listed below:

• 2020 – summer (16–17 March): Healthy Rivers

Other data: The Plain Road Upstream site is upstream of the Walpole Weir and gauging station. The gauging station is owned by Water Corporation and is known as the Plain Road Bridge gauging station (this gauging station is currently not monitored; site reference: 606003).

Search on the site code or site reference in the Department of Water and Environmental Regulation’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.

Seven native species and one non-native species were recorded at this site in the March 2020 assessment. This includes five native fish (little pygmy perch, western pygmy perch, western mud minnow, western minnow and nightfish), two native freshwater crustaceans (smooth marron and koonac) and one non-native species (gambusia).

Two species of high conservation value occur in this subcatchment. Both of which were found at this site during the March 2020 assessment. These include:

• Little pygmy perch – listed as endangered under the Biodiversity Conservation Act 2016
• Western mud minnow – listed as vulnerable under the Biodiversity Conservation Act 2016

This is the first time little pygmy perch have been recorded in this system. It was only discovered in 2008 (formally described in 2013) and is only found in restricted areas in the southern-most part of Western Australia including the Denmark, Mitchell, Hay, Kent and Walpole Rivers and Lake Smith. Little pygmy perch were found in high abundance and across a range of size classes (including juveniles), suggesting they are recruiting successfully.

The pouched lamprey (both ammocetes and adults)  were found in the Morgan and Beatty (2003) study but not detected in this assessment. The  pouched lamprey is a Priority 3 species (Poorly-known) under the Biodiversity Conservation Act 2016 (Western Australia). Priority 3 refers to possibly threatened species where data is insufficient to assess threatening processes that could affect them, also noting that 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 a number of 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.

Note: collection of fauna from inland aquatic ecosystems across Western Australia requires a license from the Department of Primary Industries and Regional Development (DPIRD) and also the Department of Biodiversity, Conservation and Attractions (DBCA). All species collected must be reported to these agencies as part of license conditions.

One south-western snake-necked turtle was recorded at this assessment site.

For more info on this and other aquatic species, please see the River Science fauna page here.

References and further reading:
Beatty S and Morgan D 2003, ‘Freshwater Fishes of the Walpole River and the impact of the weir to fish and lamprey migrations’ Fisheries Western Australia