TRAVERSE CITY, Mich. (AP) — Placing dam-like structures in Chicago
waterways would be an almost foolproof method of preventing Asian carp
from reaching Lake Michigan, while a less pricey electric barrier system
also has solid prospects for shielding the Great Lakes from the invasive
fish, according to a scientific analysis released Wednesday.
studies have weighed the pros and cons of different proposals for stopping
the carp, this one went further by rating their likelihood of success
based on "how sure experts are about each strategy," said Marion Wittmann,
a University of Notre Dame post-doctoral researcher and the report's lead
The report was
designed to help policymakers choose an effective plan that wouldn't take
too long to carry out. It determined that other methods under
consideration, such as using strobe lights and water cannons to frighten
the carp away, might also be helpful but would be less likely to succeed.
The study was
conducted by scientists with Notre Dame, the U.S. Forest Service and
Resources for the Future, an independent research institution. Their
conclusions were based on a survey of experts in fisheries management,
aquatic nuisance species and other relevant topics.
They were asked
to rate the likelihood for success of a variety of strategies for shutting
down what's considered the most direct route to the Great Lakes for Asian
carp: a network of rivers and canals around Chicago that link Lake
Michigan to the Mississippi River watershed.
finding of this study is that knowledgeable experts identified clear
differences in the likely effectiveness of some Asian carp prevention
technologies as opposed to others," said John Rothlisberger, a Forest
Service aquatic ecologists and one of the report's writers. "Physical
separation stands out from the rest as having the least associated
uncertainty and the highest probability of preventing the introduction of
Asian carp into Lake Michigan."
silver carp, which gobble huge amounts of plankton on which many native
species also subsist, were imported from Asia in the 1970s and have
infested the Mississippi and its tributaries. Scientists say if they
overrun the Great Lakes, they could upend the ecosystem and damage a $7
billion fishing industry.
The U.S. Army
Corps of Engineers this month presented eight options for fortifying the
Chicago waterways to prevent Asian carp and other invaders from migrating
between the two giant watersheds. The alternatives included walling them
off with physical structures, which could cost more than $15 billon and
take 25 years to accomplish, and other methods, including deploying
electric barriers in addition to an existing one in a canal 37 miles from
But critics say
the Corps' timetable is too slow and could allow the carp to reach the
lake before the work is done.
Authors of the
new report, which is being published in the journal Environmental Science
and Technology, said it offers one way to speed things up. By assigning
expected performance ratings to 17 possible strategies based on expert
opinion, it offers resource managers a basis for moving forward without
waiting for time-consuming field tests, Wittmann said.
"Asian carp are
so close to Lake Michigan, we don't have much time right now," she said.
The study found
that physical separation could prevent 95 to 100 percent of Asian carp
introductions into Lake Michigan. The experts acknowledged the possibility
that catastrophic flooding could overwhelm the barriers or that the carp
could reach the lake through other means, such as an angler dumping a bait
bucket containing young carp that were mistaken for other species,
concluded that the electric barrier could prevent 85 to 95 percent of carp
methods that were considered ranged from depleting oxygen or boosting
carbon dioxide levels in parts of the waterways to spreading chemicals to
blocking fish passages with nets. The report said some could have high
failure rates, although it said a combination of noisemaking devices,
bubbles and strobe lights could be 75 percent to 95 percent effective.
Duane Chapman, a
U.S. Geological Survey fisheries biologist and one of the specialists
consulted for the study, said there is no scientific consensus on how many
Asian carp would be needed to establish a breeding population in the Great
Lakes. So it isn't certain what level of barrier effectiveness is required
to thwart a successful invasion. But he said there's a significant
difference between the protection offered by physical and electric
barriers, even though their ratings in the study might not seem very far
emit an underwater current designed to repel fish and jolt those that
don't turn back. The Army Corps says the presently operating barrier is
working well, although Asian carp DNA has been found beyond it. And the
Corps acknowledged in December that small fish might be able to slip
through the barrier in water flows created by passing vessels.
barrier that the fish can't swim through is better than one they could
swim through under certain conditions," Chapman said.