- U. S. Geological Survey (USGS) scientists are making
headway in unraveling clues to the causes of massive die-offs of frogs
and other amphibians. The agency announced today (August 8, 2000) that
a little-understood, emerging iridovirus disease associated with large
die-offs of frogs and salamanders in the Midwest and the East has caused
another recent die-off, in North Dakota.
- USGS wildlife pathologist D. Earl Green said an iridovirus
infection is the culprit in most of the deaths of U.S. western tiger salamanders
at the U.S. Fish and Wildlife Service's Cottonwood Lake Study Area near
Jamestown, North Dakota.
- Wildlife health scientists at the USGS National Wildlife
Health Center in Madison, Wisconsin, also are investigating numerous other
amphibian die-offs that recently occurred or are continuing to occur in
several locations across the United States. The die-offs, which involve
multiple species of frogs, toads, salamanders and one species of newt,
are occurring on private, state, and federal lands including several national
- "The U.S. Geological Survey is leading the government's
efforts to help determine why amphibians are disappearing," said Interior
Secretary Bruce Babbitt. "This is a crisis that has attracted worldwide
concern. It requires timely, aggressive research. It is no exaggeration
to say that USGS research on these die-offs has global implications."
- Whether some of the ongoing die-offs are related to recent
local or regional amphibian declines across the United States, or are sustained,
long-term events only recently discovered, is still unknown. The wide geographic
distribution of these mortality events and the number of species involved
may represent an entirely new phenomenon or may be partly the result of
increased surveillance of amphibian populations. Amphibian researchers
and land managers worldwide, however, are concerned about the often severe
and mostly unexplained declines of amphibian populations on many continents,
including in remote and pristine areas.
- Research by USGS and other scientists has identified
many deadly virus infections and chytrid fungus as causes of some recent
amphibian die-offs and local population declines. Scientists are actively
investigating other hypotheses that could help explain these worldwide
declines, including increased exposure to ultraviolet radiation due to
ozone thinning, the spread of non-native predators, contamination from
pesticides and other chemicals, and rising temperatures. Many biologists
suspect a combination of factors may be responsible.
- At the Cottonwood Lake Study Area, sick salamanders were
first noticed in May by USGS researchers Ned Euliss and David Mushet as
they conducted amphibian sampling in one of the study area's 17 wetlands.
By July, when salamanders in the study area typically reach their yearly
peak in numbers, the researchers were only able to trap a total of eight
salamanders in the three traps they had set out. Last July, in the same
wetlands, the researchers had caught between 100 and 150 salamanders per
- The disease outbreak has spread to two other wetlands
so far; the status of salamander populations on the many wetlands off the
study site is unknown. "We've been studying amphibians in these 17
wetlands since 1992 and have other long-term data from the area since 1967,
and have never seen or recorded any die-offs due to disease," Mushet
said. Because the salamanders also exhibit unusual skin abnormalities,
USGS is conducting additional testing to rule out a concurrent infection
- Since 1996, when USGS began investigating amphibian mortality,
iridoviruses have been associated with numerous tiger salamander die-offs
in the western United States and Canada. USGS virologist Douglas Docherty
has isolated iridoviruses from tiger salamander die-offs in Idaho (1999),
Utah (1998), and North Dakota (1998), and Green has found microscopic evidence
of an iridovirus infection in tiger salamanders from Wyoming (1999). Other
researchers have confirmed iridoviruses in tiger salamander die-offs in
Arizona (1996) and Saskatchewan, Canada (1997).
- USGS has identified iridovirus as the likely suspect
in several other recent amphibian die-offs. According to Kathryn Converse,
a wildlife disease specialist at the USGS National Wildlife Health Center,
iridovirus is also the probable culprit in a late June die-off of hundreds
of spring peepers a type of frog at Acadia National Park in Maine. Also
in June, USGS scientists isolated iridovirus from mink frogs found dead
in Minnesota; from wood frogs, bullfrogs and spotted salamanders found
dead in North Carolina; and from wood frog tadpoles and spotted salamanders
found dead and dying at a Massachusetts site where several hundred to a
thousand amphibians were reported to have died. For the second consecutive
year, numerous frogs and salamanders at the Great Smoky Mountains National
Park in Tennessee experienced a spring die-off associated with iridovirus.
- USGS diagnostic work on several other recent or ongoing
amphibian die-offs has identified yet another amphibian disease, chytrid
fungus. It has been implicated as a likely cause of major amphibian die-offs
in pristine areas around the globe and has been isolated in Colorado's
Rocky Mountain National Park where state-endangered boreal toads are dying
from chytrid fungus infections that are very similar to those that killed
boreal toads in the park and other regions of the state in 1999.
- As the nation's largest water, earth and biological science
and civilian mapping agency, the USGS works in cooperation with more than
2,000 organizations across the country to provide reliable, impartial,
scientific information to resource managers, planners, and other customers.
This information is gathered in every state by USGS scientists to minimize
the loss of life and property from natural disasters, contribute to the
sound conservation, economic and physical development of the nation's natural
resources, and enhance the quality of life by monitoring water, biological,
energy and mineral resources.
- Note To News Editors: For reproducible pictures, go to
Site Served by TheHostPros