EDNA PLATYPUS RESULTS FROM THE UPPER BARWON RIVER ARE IN!

In autumn this year Corangamite CMA commissioned ecologists from EnviroDNA to conduct an eDNA survey to assess the status of platypus populations in the upper Barwon River, in addition to fish and growling grass frogs.

The innovative eDNA method, which involves collecting water samples to detect genetic material from aquatic animals, is particularly well-suited to citizen science involvement; with local volunteers, Corangamite CMA and Upper Barwon Landcare Network (UBLN) staff all taking part. In collaboration with UBLN, 17 survey sites were selected, and water sampling was undertaken during April 2024 targeting the juvenile dispersal period for platypus in Victoria.

The upper Barwon waterways have been significantly modified by land clearing, invasive species, stock access, altered flow regimes, and climate change, thus the environmental impacts on the natural values of the local waterways, including on vulnerable platypus populations, are poorly understood.

The findings: platypus DNA was detected throughout the upper Barwon River, with a stretch of no platypus or low abundance between Birregurra and Winchelsea. 53 percent of the sites surveyed returned positive results. These results are consistent with results from 2019 and 2020. The proportion of sites where platypus were detected was higher than previous surveys, with detections at several sites where they had not been found previously, and conversely no platypus recorded at three previously detected sites.

No growling grass frog eDNA was found at the four sites surveyed – it’s possible that the surveys were undertaken too late in the breeding season for them to be detected. 16 fish species were recorded. Although the fish community is dominated by introduced species such as carp, mosquitofish, redfin, and trout, the native short-fin eel was the most detected species.

A highlight of the monitoring was the detection of eDNA belonging to the endangered little galaxias, Galaxiella toourtkoourt in the east and west branch of the upper Barwon River.

These results will play a vital role in guiding future rehabilitation efforts as part of the Upper Barwon Flagship project. Key recommendations are to:

• investigate flow regimes to assess their suitability to support platypus.
• implement a consistent monitoring program to confidently understand changes in local populations.
• protect and maintain existing platypus populations in the east and west Barwon River upstream of Birregurra and the Barwon River near Winchelsea to prevent further declines; and
• improve habitat quality along the middle reaches of the Barwon River through improved baseflows and rehabilitate riparian zones to facilitate expansion of connectivity of existing populations.

For more information about the survey, please contact Bec McCristal at rebecca.mccristal@ccma.vic.gov.au