August is ‘Platypus Month’ – and it’s the best time of the year to spot them in the wild. Photo: Richard Taylor, Waterwatch.
The ACT’s waterways are becoming increasingly cleaner, leading to growing populations of their apex predators, according to local volunteer group ‘Waterwatch’.
The platypus and rakali (or water rat) sit at the top of the food chain in the local waterway ecosystem, mainly feeding on waterbugs. But if rivers become too choked with sediment, water bugs can’t survive and bring predator numbers down with them.
It’s happened in Cooma Creek.
“We’ve seen decreases particularly in the Cooma Creek and Scottsdale Reserve sites on the Murrumbidgee after the 2020 bushfires, when a lot of sediment was moving through the river and filling up a lot of the habitat spots,” Waterwatch facilitator Daniel Harris-Pascal says.
“We’re finally seeing the impact of that lessen as we move in time away from the fire.”
Waterwatch runs Platypus Month every August, inviting Canberrans to get out and spot as many platypuses as they can in the wild.
Since 2013, with funding from the ACT Government and Icon Water, it has surveyed eight sites in the ACT and surrounding region to ascertain how both this species and the water rat are doing.
Last August, about 700 people took part in the survey, either reporting sightings through the ‘Platty and Ratty Portal’ on the Waterwatch website or taking part in group ventures at dawn and dusk.
A total of 29 individual platypus and 19 water rats were detected across eight survey sites – healthy numbers for both species.
“Broadly, we see about 25 platypuses in the surveys and about 20 rakali – we have seen rakali numbers increase somewhat, and for the most part, it looks like platypus populations are stable,” Mr Harris-Pascal says.
“Obviously, in a drought year, there are fewer platypus around and surviving, and then in wetter or more abundant years, they’re back. But the main limitation for platypus, probably in our region, is habitat availability. So, it’s just about having space and then the water bugs in the water to support those populations.”
A female platypus will lay between one and three eggs at a time, and by late summer, there’ll be a “flurry of sightings” as the young not only leave the nest but are pushed out of the area by the dominant male.
“They’re definitely territorial. In our region, one platypus’s whole range could be about 7 km.”
Combined with rakali, which are largely scavengers, Mr Harris-Pascal says the recent numbers come down to “a lot of work in the ACT to improve waterways”.
“It’s one of many types of reading that we do because platypus and rakali are top-order predators, and so by checking their numbers, we can kind of – by proxy – get an understanding of the health of the underlying ecosystem.”
As Waterwatch kicks off its 12th round of surveys this August, the organisation is again calling for volunteers to help.
Queanbeyan River is always a hotspot due to its water quality, fed by the Tinderry and Googong catchments, rather than other rivers that pass through urban areas.
“Obviously, with the Murrumbidgee, there’s not quite enough flow in the river and it also moves through Cooma and Tuggeranong, and all of that, so Queanbeyan’s got this Goldilocks thing where it’s an urban river, but the catchment for the river is not,” Mr Harris-Pascal says.
“We’re keen to see that persist, particularly as Googong and those areas grow.”
Waterwatch would also like to see more sightings in three key areas, including Ginninderra Creek below Lake Ginninderra, the Gudgenby River in Namadgi National Park, and the Yass River and its tributaries.
“No confirmed sightings of platypus have been received in this section of the Ginninderra Creek since the lake was built in the 1980s,” the Waterwatch website says.
Scouring waterways for the elusive platypus. Photo: Waterwatch.
It’s a similar story for the Yass River, with only a handful of “anecdotal sightings”.
The Gudgenby River catchment was historically home to platypus, but sightings have dried to zero since the 2020 bushfires, which devastated the area.
“The main river and its tributaries in the top half of the catchment (within Namadgi National Park), such as Bogong Creek, Rendezvous Creek and Dry Creek, would be of interest. Also, the lower section of the Orroral River (top section is still off limits due to fire damage) has limited historical data and sightings here would be welcomed.”
For more information on how to take part in Platypus Month, visit Waterwatch.