By JOHN FLESHER | Associated Press
TRAVERSE CITY, Mich. (AP) — Asian carp
are reproducing in more places and under more varied conditions than
experts had believed they could, yet another reason to worry about the
greedy invader's potential to infest waterways and crowd out native
species, scientists said Tuesday.
Several varieties of carp imported from Asia have migrated steadily
northward in the Mississippi River and its tributaries since escaping
from Southern fish farms and sewage treatment ponds in the 1970s.
They've been spotted in more than two dozen states. Bighead and silver
carp gobble enormous volumes of plankton, a crucial link in the aquatic
food chain, while silver carp sometimes collide with boaters by hurtling
from the water when startled.
Research based largely on data
from their homeland has indicated the carp can spawn successfully only
under the right circumstances, including temperatures of about 70
degrees and long stretches of continuously flowing water where
fertilized eggs can drift while incubating. But a study led by Reuben Goforth of Purdue University has found their eggs in places that previously were considered unsuitable.
"We need to recognize that these
species have greater flexibility ... than perhaps we originally thought,
so we probably need to be prepared for them to become established in a
wider range of ecosystems than we originally expected," Goforth said in a telephone interview.
The findings are particularly sobering for the Great Lakes, where
scientists say the carp could threaten the $7 billion fishing industry
if they spread widely. None are known to have reached the lakes,
although their DNA has been found in Lake Erie and in Chicago waterways a
short distance from Lake Michigan. A federal study last year identified
three rivers that flow into Lake Erie as good candidates for Asian carp
nurseries.
Goforth, an assistant professor of forestry and natural resources,
said he and his colleagues focused their study on the Wabash River in
Indiana. Authorities have built a fence in the Fort Wayne area to
prevent the carp from migrating from the Wabash to the headwaters of the
Maumee River, a Lake Erie tributary regarded as ideal spawning habitat.
The Purdue team, assisted by the Indiana Department of Natural
Resources and the U.S. Geological Survey, collected water samples
containing Asian carp eggs in 2011 from sections of the river that were
much shallower and narrower than had been considered necessary for
spawning, Goforth said. Some were found 50 miles upstream from known
spawning areas.
Another surprise was the discovery of drifting eggs as late as
September, contrary to previous belief that the spawning season ends in
July.
"What's particularly interesting to me is that they're showing more
flexibility here than in their native range," Goforth said. Ironically,
while Asian carp are spreading rapidly in the U.S., they're declining in
China, where dam projects are reducing their habitat.
Further research is needed to determine whether eggs laid in more
remote stretches of the river are surviving to adulthood, he said.
Duane Chapman, a USGS research fisheries biologist and Asian carp
expert who didn't participate in the Purdue study, said the new findings
were important because Asian carp have been widely regarded as "large
river spawners."
The Wabash is "probably the smallest river in which we are aware of
Asian carp spawning," Chapman said. "One of the big questions we're
dealing with, particularly in the Great Lakes, is which tributaries
might be potential spawning sites or what reservoirs are potentially at
risk ... and how far upriver it goes."
report is erroneous as the International Game Fish Association, which keeps world records, lists a 41-pound, 8-ounce brown trout as the all-tackle world record.