Platypuses recovering from bushfire effects

Bushfires have a devastating impact on all facets of life, including on biodiversity and native animals. Following the 2019–20 bushfires, however, the platypus population in north-east Victoria is stronger than expected.

To measure platypus numbers, researchers from the Australian Platypus Conservancy set nets in four locations along the Buffalo River near Myrtleford, Victoria. The study found 12 platypuses — more than the researchers expected.

According to biologist Geoff Williams, the animals most likely survived the bushfires because they were normally in the water or in their burrows underground.

Half the animals that were found by researchers were juveniles, pointing to a successful breeding summer season.

"We don't know how that compares with the pre-fire numbers, because unfortunately we didn't have any survey work prior to the fires to give us a number," Williams said.

"All the indications are it's a healthy population, and the fact that so many juveniles have been produced this breeding season means if there was any shortfall, we would be very confident the numbers will be made up very quickly by this year's juvenile cohort."

Williams says the strong platypus numbers demonstrated the hardiness of the species.

"They're often described as shy and sensitive, but in fact we think they're probably a lot more resilient than perhaps they're probably given credit for,” he said.

“This is a species that has been around for millions of years in one form or another and I think they are very flexible in terms of their response to problems that they face, in terms of drought and bushfires and floods."

Every bushfire situation is different, however, and the aftermath of different fire seasons can vary greatly. While the results from the survey are encouraging, Williams cautions against drawing too many conclusions.

"Some areas are more intensely burnt than others and if the creek in a particular river is [at a] low level, then perhaps the level of ash and sludge that gets into the water is higher in intensity,” he said.

One species that did not fare so well was the critically endangered Macquarie Perch. Researchers from the Department of Environment, Land and Planning (DELWP), with the Arthur Rylah Institute of Environmental Research, conducted surveys in the upper Buffalo River to understand how the species were impacted by the bushfires.

According to the research, while the Macquarie perch numbers were reasonably healthy immediately following the fires, the rain that followed the blaze washed ash and sediment into the river.

"It was pretty grim in a way, because it's demonstrated that the post-fire impacts — particularly the rain and sediment — have really had a significant impact on the species," said Biodiversity Recovery Coordinator, Glen Johnson.

"It's weeks and, in fact, months later that those impacts were really having the greatest effect and so when we have the high amounts of ash and sediment, the fish really just end up being in a really critical situation and can die."

DELWP undertook emergency fish salvage operations following the fires and some fish were returned to the rivers this past June once the water quality improved. In January, 12,000 fingerlings were released into the upper Buffalo.

Slightly older fish will soon be transferred into the river from Lake Dartmouth in order to increase genetic diversity.

"We're getting some good genetics from another healthy population, so we're improving that genetics stock and that improves the resilience," Johnson said.

"It means that small relic populations, as is the case with the upper Buffalo Macquarie perch population, have probably got a little bit bigger and have a greater capacity to withstand future events."