Mich. (AP) - Asian carp are unlikely to reach the Great Lakes by stowing
away on commercial vessels in Chicago-area rivers and canals, the U.S. Coast
Guard said Thursday.
Even if the
invasive fish somehow got into the ballast tanks of vessels early in their
life cycle, they almost certainly would be killed in pumping mechanisms
through which they’d have to pass to return to open water, researchers found
in a recent study. Ballast tanks are the compartment of a ship that holds
water, which helps it maintain buoyancy.
Scientists with the
Coast Guard Research and Development Center and the U.S. Environmental
Protection Agency conducted experiments in a section of the Illinois River
called the La Grange Reach, where Asian carp are well established.
Bighead and silver
carp imported from Asia decades ago have infested the Mississippi River and
many of its tributaries. An electric barrier in a shipping canal near
Chicago is meant to keep them from migrating into Lake Michigan, where
scientists say they eventually could spread to the other Great Lakes and
out-compete native fish for food.
But scientists in
recent years have detected DNA from Asian carp in waterways beyond the
barrier, sparking debate over its effectiveness. Some advocates want
billion-dollar barriers constructed to seal off Lake Michigan from the
Mississippi watershed, which opponents say would disrupt shipping traffic
and cause flooding around Chicago.
State and federal
experts are studying whether the DNA could have come from sources other than
Asian carp. They’re also considering ways the fish might be evading the
barrier. One theory is that carp eggs, larvae or recently hatched fish might
slip through cracks in hulls of barges and tugboats and enter the ballast
tanks. If they survive as the vessels move through the electric field,
perhaps they could escape back into the water on the other side.
But results of the
study show only a “minimal risk” of that happening, the Coast Guard said in
a news release.
The Coast Guard
researchers cut 3-inch holes on the exterior of a barge’s ballast tanks and
installed valves to determine whether larvae could get inside through hull
ruptures. They also placed carp larvae inside a tank to monitor how long
they’d survive and pumped water out of the barge tanks to see if larvae
could live through the process.
A few tiny fish did
get into the tanks, and the water inside had enough oxygen for them to
survive temporarily, said Scott Anderson, chief of the prevention division
for the Coast Guard’s 9th District in Cleveland. But almost none made it
past the spinning rotor inside the pump that empties the tanks, he said.
“If they actually
were able to get into (the ballast tanks) through cracks or holes, which was
found unlikely, the mortality rate was over 99 percent when they were pumped
back out,” Anderson said.
The study was funded through the
Great Lakes Restoration Initiative, an Obama administration program aimed at
making progress on some of the region’s biggest environmental problems. A
detailed report is scheduled for release later in March.