Oldest-known wild platypus gives new insights into longevity of enigmatic Australian species
A 24-year-old male platypus is released back into Monbulk Creek after being examined during a survey. (Supplied: Alice Ewing/Ecology Australia)
Gemma Snowball didn't make too much of the tag on the platypus pulled from a Melbourne creek last autumn.
Melbourne Water had been backing surveys of the city's platypus (Ornithorhynchus anatinus) populations since the 1990s so a tag was not unusual.
Stamped "01F6-03FF", all the zoologist for Ecology Australia knew was the male had been captured before.
"I didn't know the significance of the platypus age until a few days after when checking the data and talking to other biologists," she said.
"I was quite shocked and excited when I found out."
The tag dated all the way back to late 2000 when the male specimen from Monbulk Creek, one of 10 distinct Melbourne platypus populations, was estimated to be just over a year old.
He was bagged, measured and weighed a second time late last year in another platypus survey.
Ms Snowball and her colleagues calculated the duck-billed buck was about 24 years old, according to a study published in Australian Mammalogy.
That's a new record for a wild platypus.
It is three years older than another Victorian male and a female from the Shoalhaven River in New South Wales.
A previous long-term study of Melbourne platypuses found about 25 per cent of captured animals were older than nine, 36 per cent were six to eight and 40 per cent were three to five years old.
The 24-year-old male platypus tagged 01F6-03FF is measured and weighed. (Supplied: Alice Ewing/Ecology Australia)
Getting to 20 in the wild has been biologically possible if not a common phenomenon in surveys of the svelte monotreme, egg-laying mammals, found from Cooktown in North Queensland to Tasmania.
Surviving the extremes
Australian Platypus Conservancy conservation biologist and study co-author Melody Serena said finding a 24-year-old platypus was "gobsmacking".
Dr Serena came from the United States to Australia to study chuditch, a type of spotted quoll, before starting work with platypus a few decades ago.
She said 21 was about the maximum life span scientists had thought the platypus could reach in the natural world.
The age of a male platypus in the wild could depend on the density of the species. (Getty Images: Libor Vaicenbacher)
But the Monbulk Creek male had grown even older and was still healthy and appeared to be sexually active.
"The other thing about this male was he was first caught in 2000, the Millennium Drought was just coming into play to be a major problem in south-eastern Australia," Dr Serena said.
"Monbulk Creek is a small creek [about 6.2 megalitres of daily discharge] ... during the Millennium Drought there was often no flow.
"We did a lot of surveys there in 2007 that confirmed that the population was virtually not reproducing because the food supply was so poor."
But the Monbulk Creek male got through not just the drought, which lasted from 2001 to 2009, but also serious flooding.
Dr Serena said longevity in the platypus appeared to be an adaptive pattern that allowed them to continue to get through tough times.
"Because they have this capacity to live for a long period of time when conditions are right, they can survive," she said.
LoadingLess competition, fewer problems?
The new age record also potentially shows how different environmental conditions can influence the aging of wild platypus — a species listed as near threatened nationally but endangered in South Australia and vulnerable in Victoria.
Monbulk Creek is a fairly isolated population of the species, with about 12 to 29 individuals making up the group between 1997 and 2007.
There's an even sex ratio and about 1.6 platypus for every kilometre of creek.
In comparison, the Shoalhaven River has 12 platypus for every kilometre and a sex ratio favouring females at about 84 per cent of adults and sub-adults.
Male platypus in denser populations like the Shoalhaven River have been found to only live to about seven years old. (Supplied: Zoos Victoria)
Most males in the river did not get past the age of seven with only one individual reaching eight, based off long-term studies by Tom Grant, an ecologist at the UNSW.
Dr Serena said while the Shoalhaven males might breed well, there could be a trade-off because of territorial fighting, associated stress and less feeding contributing to a shorter life span.
She said the different ages recorded in various locations showed the importance of not relying on limited assumptions of age when undertaking conservation modelling.
"Longevity might depend on population density," Dr Serena said.
Just how old can a platypus live?
We're still learning about the upper limit of platypus longevity and what the species can do in captivity without predation pressures.
But a female platypus called Fleay (so named after David Fleay who was the first person to breed the species), that turned 30 in October is giving us the best idea of what is possible.
The Healesville Sanctuary resident has been breaking the record for the oldest-known platypus in the world every year since her mid-20s.
Healesville Sanctuary is home to both a 30-year-old female platypus and a 25-year-old male platypus. (Getty Images: Jason Edwards)
The zoo's platypus specialist Jessica Thomas has been working with Fleay for the past 16 years.
She said the platypus had exceeded expectations with how long she had lived.
"Fleay is certainly teaching us how old a platypus that is cared for can live to," Dr Thomas said.
"She has reduced eyesight and hearing, but as a platypus that lives in a sanctuary it doesn't impact her quality of life too much."
Despite diminishing senses, Fleay's keepers say thanks to her electro and mechanosensory abilities she can detect prey in the water with her eyes closed.
A ramp has also been installed to help her get in and out of the water but Fleay hasn't had to use it yet.
Surprisingly the old platypus has not developed any arthritis compared to other old mammals.
Dr Thomas said this might be because of an aquatic lifestyle that did not put low pressure on her joints and a diet of yabbies which are full of calcium and fatty omega-3 fatty acids.
"Despite her age, Fleay still enjoys ripping apart paperbark logs and tree fern trunks," she said.
Ultimately, Dr Serena said a platypus in its mid-20s was about as old as you could expect in the wild and given Fleay's aging signs, it was not likely the species could get a lot older.
"We don't ever expect to see a 50-year-old platypus or 100-year-old platypus," she said.