Cosmos,
The Science of Everything by Dyani Lewis 1/14/19
It
was a warm February evening in 2015 and Sydney’s Taronga Zoo had emptied of
visitors for the day. But behind closed gates, Karrie Rose and her team were
gearing up for a long night. Their task: to find out what was killing the rare
Bellinger River snapping turtle (Myuchelys georgesi).
Two
days earlier, the NSW Office of Environment and Heritage (OEH) had launched an
investigation following reports from kayakers of sick and dead turtles.
Whatever had turned their home, five hours’ drive north of Sydney, into a
killing field looked like it could push the species to extinction in a matter
of weeks.
The
20 snapping turtles that landed on Rose’s doorstep were blinded and covered in
ulcers, emaciated and lethargic. Their prognosis was grim.
“It
was really dramatic,” said Rose, head wildlife vet at the Australian Registry
of Wildlife Health at Taronga Conservation Society. “I’d never seen anything
that acted that quickly in the wild.”
Into
the early hours of the morning, Rose and her team measured, photographed and
dissected the turtles to glean as much information as they could about the
mysterious illness that was leaving two other species of turtle in the river
unscathed.
The
disease, Rose thought, had all the hallmarks of an infection. “It was highly
inflammatory,” she said, “so it really suggested that there was an infectious
agent in there.” Finding no signs of bacteria, fungi or parasites, she narrowed
her focus to ranavirus, which had been implicated in mass mortality events in
other turtle populations.
To
test her hunch, and every other possibility, diagnostic and research labs
around the country were enlisted to assist in the reptilian whodunit. As a
result, ranavirus and an array of other known diseases were quickly ruled out.
One
of the recipients of turtle blood, snot and body organs was Peter Kirkland, an
animal virologist at the Elizabeth Macarthur Agricultural Institute in
Menangle, an hour south-west of Sydney. Within weeks, Kirkland’s team had
coaxed viral particles to blossom in flasks of cells inoculated with diseased
turtle tissue. From the virus-laden flasks, they were able to extract and then
sequence the virus’s genetic essence – its nucleic acids.
Kirkland
not only discovered that the virus was completely new to science, he also was
able to fashion a rapid diagnostic test for the illness, now known as Bellinger
River Virus. To check that it was the virus that was making the turtles sick,
his team tested the tissue samples Rose had sent him. Some samples, he said,
had “extremely large quantities of the virus”.
The
test quickly became a central tool in parallel efforts set in motion just days
after the first reports of dying turtles came in. The goal was to prevent
annihilation of the remaining snapping turtles and save the species from extinction.
During
the rescue mission, coordinated by a recovery team at the OEH, park rangers and
biologists scoured the turtle’s habitat. As the death toll climbed to several
hundred – a devastating blow to a population of only a few thousand – 17
healthy looking turtles were spirited away to hastily constructed quarantine
facilities at Western Sydney University, under the care of turtle ecologist
Ricky Spencer.
The
turtles remained healthy, and Kirkland’s diagnostic test eventually confirmed
they were free of the virus that he’d isolated in his lab. Also virus free are
53 turtle hatchlings – and counting. The medallion-sized youngsters are the
products of an unexpectedly successful captive breeding program established at
Taronga Zoo with 16 of the survivors.
“They
are the future for these animals,” said Adam Skidmore, a reptile keeper who
oversees the Taronga program. A second insurance population also has been
established at Symbio Wildlife Park in Helensburgh, about 45 kilometres south
of Sydney’s CBD.
While
the turtles thrive in their artificial ponds – away from hungry foxes, and with
a plentiful supply of food – the future of the snapping turtle back in its home
hangs in the balance. Nobody can say where the virus came from – “the million
dollar question,” said Kirkland – or whether it lingers still in the waters of
the Bellinger.
Regardless,
the OEH recovery team is already gearing up to release 10 of Skidmore’s turtles
into the Bellinger River this summer, where they will be periodically tested
for signs of the virus.
They
won’t be alone. In a bizarre twist, biologists monitoring the river discovered
that the virus took out virtually all the adults but left juvenile turtles
unharmed. “Were they infected, or were they just not exposed?” asked Rose. Kirkland
is working on a test to answer that question.
If
it turns out that juveniles can withstand infection and develop immunity, then
careful inoculation of youngsters prior to release could safeguard them against
future outbreaks.
Protecting
the population will require more than just ensuring the river is disease free.
It’s likely that other factors – droughts sparked by climate change, say, or a
diminishing food supply – helped create a “perfect storm” that led to the
outbreak being so deadly. “It’s rarely just one thing,” said Rose, who has seen
an uptick in wildlife outbreaks in recent years. “It’s a trend that’s happening
globally.”
Devastating
disease isn’t the only threat to the survival of the species. Another, and
perhaps more immediate danger comes from one of its close relatives, the Murray
River short-necked turtle (Emydura
macquarii). Since the outbreak, this interloper has thrived in the
Bellinger River – more so, perhaps, than in its native habitat west of the
Great Dividing Range, where its populations are dwindling.
The
two turtles can interbreed to produce genetic hybrids. That’s bad news for the
snapping turtle, because repeated hybridisation with the now abundant
short-necked turtles could send it down a slow path to oblivion.
Decisions
will need to be made quickly. Juveniles in the Bellinger River are approaching
their breeding age of eight-to-ten years, so working out how to manage the
short-necked turtles will be “critical”, says Gerry McGilvray, who heads
snapping turtle recovery efforts at the OEH. She’s convening an expert workshop
early in 2019 to come up with a plan.
For
Spencer, the solution, from an ecological point of view, is a no-brainer: “You
take [the short-necked turtles] out and euthanase them.” But, he says, with a
public that’s often loath to kill any wildlife – introduced or otherwise –
“conservation biology is a little bit more than just ecology”.
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