TRAVERSE CITY, Mich. (AP) - Live Asian carp don’t necessarily have to be
present for their DNA to turn up in the environment, according to a
government study released Wednesday that could intensify the debate over how
to prevent the aggressive, hungry invaders from reaching the Great Lakes and
other vulnerable waters.
DNA is found in excrement, slime and scales from live fish. But the report
by three federal agencies identifies six other possible means through which
genetic fingerprints from bighead and silver carp could find their way into
locations such as the Chicago waterway system and western Lake Erie, where
it has been detected in dozens of samples taken in recent years.
Those potential pathways include storm sewers, fisheries sampling gear,
fish-eating birds, dead fish carcasses, barges and sediments, the report
said. It said carp DNA attached to any of those sources could remain for
days before disintegrating.
Scientists with the U.S. Army Corps of Engineers, the U.S. Fish and Wildlife
Service and the U.S. Geological Survey are conducting a three-year study
designed to answer questions raised by the repeated discovery of Asian carp
DNA in rivers and canals in the Chicago area - including locations beyond an
electric barrier intended to block the carp’s northward march toward Lake
Michigan. Their DNA also has been found in the Mississippi River beyond
“The purpose ... is to improve the understanding and interpretation of Asian
carp environmental DNA results, so we can refine and make this relatively
young monitoring tool the most effective to detect live Asian carp
presence,” said Kelly Baerwaldt, an Army Corps fisheries biologist and Asian
carp program manager. Additional reports are planned as the study continues.
Bighead and silver carp escaped into the Mississippi River from sewage
treatment ponds and fish farms in the Deep South decades ago and have
migrated northward, invading numerous tributary rivers. The filter feeders
gobble massive volumes of plankton - microscopic plants and animals crucial
to aquatic food webs.
Scientists say if allowed to infest the Great Lakes, the carp eventually
could crowd out native species, endangering the region’s $7 billion fishing
industry. Silver carp, which spring from the water when startled and have
collided jarringly with boaters, pose a threat to tourism.
Some state and local officials in the Great Lakes region want structures
placed in the Chicago waterways to seal off Lake Michigan from the
Mississippi watershed. Business and government leaders in Chicago say that
would devastate shipping in the area, and some question whether the DNA
findings are sufficient evidence that the carp have evaded the electric
Just one live carp has been found beyond the barrier, which is in a canal 37
miles southwest of the city, despite intensive netting operations after
repeated positive DNA findings.
Asian carp DNA discoveries also have ignited a debate over whether to close
a Mississippi River shipping lock in Minnesota’s Twin Cities area.
In their report, the federal scientists said they have conducted experiments
to determine the feasibility of alternative explanations for the sampling
results. Skeptics have suggested the previously detected DNA could have come
from excrement of birds that feed on dead carp, or perhaps from ice and
wastewater flushed into Chicago sewers from markets that sell the carp, or
from boats that touched the fish.
Without taking sides in the debate, the scientists found that fish-eating
birds “have the capacity” to transmit carp DNA in their droppings, which
could contaminate barges and other vessels. They found the telltale DNA in
feces of birds that were fed Asian carp.
The study also found “considerable amounts” of DNA stuck to boat hulls,
which can remain for days “and does not appear to be completely or quickly
washed off of boats moving through the water.”
Team members reported finding Asian carp DNA in Chicago’s storm sewers. They
said boats, nets and other gear used by commercial fishermen and natural
resource agencies could spread the genetic markers.
Chris Jerde of the University of Notre Dame, who’s among the scientists who
have detected Asian carp DNA in recent years, said they never claimed that
all the positive hits came from live fish. But alternatives suggested in the
report don’t explain the persistent DNA findings in the same general
locations, he said.
Jerde said he and colleagues have tested more than 1,700 water samples from
the Chicago waterways, Lakes Michigan and Erie, and many rivers in the
region. The positive results have been concentrated in areas relatively
close to where a live carp was landed in Chicago in 2010 and where a bighead
was caught in Lake Erie around 2000, he said.
“These patterns ... would seem to indicate that there’s at least some live
carp present in the system, although we don’t know how many,” Jerde said.