CITY, Mich. (AP) - At least some Asian carp probably have found their way
into the Great Lakes, but there’s still time to stop the dreaded
invaders from becoming established and unraveling food chains that support
a $7 billion fishing industry and sensitive ecosystems, according to a
scientific report released Thursday.
by experts who pioneered use of genetic data to search for the aggressive
fish, the paper disagrees with government scientists who say many of the
positive Asian carp DNA hits recorded in or near the lakes in recent years
could have come from other sources, such as excrement from birds that fed
on carp in distant rivers.
most plausible explanation is still that there are some carp out there,”
Christopher Jerde of the University of Notre Dame, the lead author, told
The Associated Press in a telephone interview. “We can be cautiously
optimistic ... that we’re not at the point where they’ll start
reproducing, spreading further and doing serious damage.”
paper summarizes findings by Jerde and other scientists from Notre Dame,
The Nature Conservancy and Central Michigan University during two years of
searching the Great Lakes basin for Asian carp. The fish have migrated
northward in the Mississippi River and many tributaries since escaping
from Deep South ponds in the 1970s. Scientists fear they will out-compete
prized sport and commercial species.
particular concern are silver and bighead carp, which gorge on plankton -
microscopic plants and animals that virtually all fish eat at some point.
The carp reproduce prolifically, and the biggest can reach 100 pounds.
September 2009 and October 2011, Jerde and his colleagues collected more
than 2,800 water samples from parts of the Great Lakes and tributary
rivers. The samples were poured through microfiber filters to extract DNA,
which fish shed in their excrement, scales and body slime. It’s known as
environmental DNA, or “eDNA.”
analysis turned up 58 positive hits for bighead or silver carp in the
Chicago Area Waterway System - a network of rivers and canals linked
directly to Lake Michigan - and six in western Lake Erie. Some of the
Chicago DNA was found in Lake Calumet, where a live bighead carp was
caught in 2010.
would say there’s at least some evidence for Asian carp being present in
southern Lake Michigan,” Jerde said. “The question is how many.”
recently, sampling by the U.S. Army Corps of Engineers and other federal
agencies also yielded positive results in the Chicago waterways. But while
the government team acknowledges the presence of Asian carp genetic
fingerprints, it disagrees that they necessarily signal the presence of
issue is significant because it could influence the debate over whether to
seal off Lake Michigan from the Chicago waterways, a mammoth engineering
task that would cost billions of dollars and take years to complete. Five
states sought that step in a lawsuit dismissed by a federal judge last
December. Under pressure from Congress, the Army Corps of Engineers has
pledged to offer options for preventing species migrations between the
Great Lakes and the Mississippi River watershed later this year.
Army Corps contends an electric barrier in a canal 37 miles from Chicago
is preventing the carp from getting through, even though their DNA has
turned up repeatedly on the other side. In a February report, federal
agencies said the genetic material could have been transported by bird
feces, fish sampling gear, barges and storm sewers.
the Jerde team’s paper, published online Thursday by the Canadian
Journal of Fisheries and Aquatic Sciences, argues that the likeliest
explanation remains the presence of live Asian carp. It’s probably no
coincidence that many of the positive samples have come from Chicago’s
Lake Calumet and western Lake Erie, where three bigheads were snagged in
1995 and 2000, the paper says.
says the scientists found no signs of the carp in Chicago locations where
they should have been abundant, such as sewer outfalls, if the alternative
explanations were accurate.
secondary alternatives are even less plausible for Lake Erie, the paper
says. The DNA that was found there was more than 100 miles from waterways
infested with Asian carp. So if birds were the source, it seemingly would
mean they feasted on carp, flew a long distance and excreted feces within
a few hours of when the researchers collected water samples.
requiring all kinds of random events to happen simultaneously,” said
Lindsay Chadderton of The Nature Conservancy, who contributed to the
paper. “It’s possible, but highly unlikely.”
Baerwaldt, a fisheries biologist and Asian carp program manager for the
Army Corps who supports the alternative-source theory, said the new report
didn’t change her mind. Fish-gobbling birds such as cormorants often
range over hundreds of miles, she said. And if live carp are the only
source of the DNA in Chicago, why has just one been found beyond the
electric barrier? (Jerde says they’re notoriously hard to catch.)
it could be live fish and it also could be these other things, because we
tested them and looked at the evidence,” Baerwaldt said.
Army Corps, the U.S. Fish and Wildlife Service and the U.S. Geological
Survey continue to study the issue and hope within a couple of years to
refine methods of determining the likely source of a particular DNA
sample, she said.
bottom line is there’s just a lot we don’t know about eDNA,” she