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.
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
The study was conducted by scientists with the University of
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.
“An important 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.”
Bighead and 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 recently 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 Lake Michigan.
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, said Marion
Wittmann, a Notre Dame post-doctoral researcher and the report’s lead author.
“Asian carp are so close to Lake Michigan, we don’t have
much time right now,” Wittmann said.
The study found that physical separation could prevent 95
percent 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, Wittmann said.
The experts concluded that the electric barrier could
prevent 85 percent to 95 percent of carp introductions.
Other deterrent 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.
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