Molly Murray, The
(Wilmington , Del. ) News Journal 7:55 p.m. EDT June 2,
2014
A virus partially blamed for a worldwide amphibian
decline has made its way to Delaware ,
killing tadpoles and raising fears it will spread to reptile species.
The ranavirus, a type of virus that affects
cold-blooded species, has been found in wood frog tadpoles in all of Delaware 's counties and eight in Maryland . And there is concern it could
impact iconic reptile species like the Eastern box turtle or endangered species
like the bog turtle.
"Of 23 Delaware
ponds tested in 2013, ranavirus was detected in 14 – 61 percent – and amphibian
die-offs were recorded for two of those during the sampling period," said
Holly Niederriter, wildlife biologist with the state's Species Conservation and
Research Program.
In addition, a dead bog turtle found three years ago
in Delaware
likely died from a predator attack but it was infected with ranavirus, herpes
and mycoplasma, she said.
Tracking the potential impact on relatively secretive
turtle species is difficult, why is why Niederriter has been out again this
year re-sampling ponds. She is finding similar signs of the virus.
She said that infectious diseases such as ranavirus –
which is likely spread by contact with water or sick or dead tadpoles – are a
large cause of the worldwide amphibian decline.
The disease is found throughout the United States
in both frogs and turtles but it has not been found in birds or mammals. With
some tadpole frog species, the mortality rate is as high as 99 percent.
"The virus can also be spread via water, in soil
and on the boots, nets and gear of humans," Niederriter said.
The ranavirus was identified in Maryland
in 2001 in Prince George 's
County, said Scott Smith, a wildlife ecologist with the Maryland Department of
Natural Resources.
A researcher at Towson University
put radio transmitters on Eastern box turtles to see how they would fair if
they were moved to new locations as part of a road construction mitigation
project.
But the transmitters turned up something unexpected.
"They'd be sick one day and dead the next,"
Niederriter said.
Smith said the researcher lost both his control site
and his two test plots to ranavirus in the study that took place from 2008 to
2011.
One reason for the concern, Smith said, is that box
turtles are long-lived and have reproductive strategy that differs from frogs.
Frogs typically lay eggs in woodland ponds by the hundreds.
But box turtles, while laying several clutches of
eggs, may only lay three to eight at a time.
Smith said with frogs, especially wood frogs, the
disease seems to have highest impact on the tadpoles but doesn't kill adults.
That means the adults, which typically live five to eight years, can return to
breed again the following year.
There are species, like bullfrogs, that appear more
resistant to the disease, he said.
So far, researchers believe the disease in our area
has the greatest impact on wood frogs and spotted salamanders. No one is
certain how it spreads from pond to pond, though there is some thought that
other wildlife may spread it, including bullfrogs, which can travel three miles
to breeding pools.
Researchers have found that one day a pond can seem
fine and then the entire wood frog tadpole population can be wiped out in as
little as five days.
Over several days in late May, Niederriter and
research assistant Christine Tilton set out to sample wood frog tadpoles.
The two scientists waded into slightly less than knee
deep water at Blackbird
State Forest .
In March, they marked the areas where wood frogs laid their egg masses with
orange survey tape.
Last week, they took long-handled nets and swept
through the leaves and water in the survey area, searching for inch-and-a-half
long tadpoles.
They needed 30 animals, which they collected in a
bucket and took back to a test site in a cleared area in the woods.
"They have to be a certain age," Niederriter
explained. The telltale sign is that the tadpoles are starting to develop legs.
At this stage of development, the tadpoles may even show signs of the disease –
red splotches.
For this study, the tadpoles are killed with a numbing
agent before being examined because they must be sent out to a lab for positive
confirmation of the disease.
"This year we're finding die-offs in more
of the ponds," Niederriter said.
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