Scientific American - USA (2019-07)

18 Scientific American, July 2019

DANITA DELIMONT

Alamy

ADVANCES

CONSERVATION

Slow-Motion

Extinction

Turtles’ famed longevity can mask

their decline—until it is too late

Nearly four decades ago zoologist Mi­

chael Thompson, then at the University of

Adelaide in Australia, made an alarming

discovery: invasive red foxes were gobbling

up more than 90 percent of all the turtle

eggs laid along the banks of Australia’s

Murray River. Thompson’s surveys also re­

vealed a disproportionate number of older

turtles, suggesting that fox predation had

already reduced the amount of juve niles in

the river. If no one took action, he warned,

the formerly abundant turtles would even­

tually disappear.

Very little was done, and Thompson’s

prediction now appears to be on its way to

coming true. A recent study confirms that

several turtle species have either drastically

declined or disappeared from various sec­

tions of the Murray River. “The problem is

that the longevity of turtles gives the per­

ception of persistence,” says Ricky Spencer,

an ecologist at Western Sydney University

and a co­author of the study, which was

published in February in Scientific Reports.

“It’s human nature that only when some­

thing is gone do we start missing it.”

Spencer and his colleagues tallied pop­

ulations of three once common turtle spe­

cies—the broad­shelled turtle, the eastern

long­necked turtle and the Murray River

turtle—at 52 sites along the southern

reaches of the river. The researchers in ­

ferred the species’ population sizes from

the number of individuals they trapped in

a given amount of time. They found the

turtles have been extirpated in places

where they were previously abundant, and

most of the specimens they managed to

capture elsewhere were large—and likely

old—adults. Spencer and his colleagues

blame the losses on ongoing nest predation

by foxes, compounded by other problems,

including environmental degradation and

severe drought in the 2000s.

“We have known about [the turtle die­

off] for decades, and despite intense media

hype in Australia about the ‘plight of our riv­

ers,’ nothing has been done to reverse that

decline,” says Rick Shine, a herpetol o gist at

Macquarie University in Sydney, who was

not involved in the research. “This paper is

a wake­up call that unless we begin to do

something about turtle conservation on a

landscape scale, we may lose a fas cinating

component of our native fauna.”

The turtles could recover quickly if

action is taken to protect nests from foxes

and restore habitat, Spencer notes. But

governments tend to respond only when

losses reach crisis levels, and the Murray

River species currently lack federal protec­

tion, he says. He and his colleagues have a

work­around, however: “Our next step

is to start designing community conserva­

tion efforts for common turtle species,”

he explains, “so people can actually do

things without having to wait for gov­

ernment funding.” — Rachel Nuwer

Juvenile Murray River turtle ( Emydura

macquarii ). Such turtles are growing rarer.

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