By Andrew Stern
CHICAGO (Reuters) - Voltage coursing through electrical barriers designed to keep invasive Asian carp out of the Great Lakes may need to be raised to keep out juvenile fish, U.S. officials said on Friday.
The Army Corps of Engineers has mounted a multimillion-dollar effort to keep voracious Bighead and Silver Carp that now infest the Mississippi River Basin out of the Great Lakes, where scientists predict they could decimate the lakes' $7 billion fishery.
"The current barrier operating parameters are effective for fish as small as 5.4 inches in length," the U.S. Army Corps of Engineers said in a news release.
"The research published in this report suggests that slightly higher operating parameters than those currently in use may be necessary to immobilize all very small Asian carp, as small as 1.7 to 3.2 inches in length."
Juvenile carp can swim 37 miles by the time they reach 6 inches in length.
Environmentalists and several state governments have fought to create a permanent ecological separation between the Mississippi River basin and the Great Lakes.
The U.S. Army Corps of Engineers, other federal agencies and Chicago-area governments have joined commercial shippers, sightseeing operators and recreational boaters in an bid to keep the waterways open.
For now, officials say smaller, juvenile carp are well downstream from the three electrical barriers on the canal that links the river system to the Great Lakes, so the two-volt current laid down by the barriers will be maintained.
The best estimate of a potentially reproducible population of Bighead carp is 25 miles downstream from the barriers, Charles Wooley of the U.S. Fish and Wildlife Service said.
Lock and dam structures have impeded the carp's progress, Wooley said, and agency crews will be vigilant during the summer spawning season to kill carp in the pools between dams.
A U.S. study to be completed this spring will determine the impact on barges and barge operators if the voltage in the barriers is raised to 2.3 volts, which laboratory tests show is sufficient to repel the juvenile carp.
Army Corps Major General John Peabody stressed that the voltage impact on the juvenile carp was measured in a laboratory, and "needs to be validated" in the field.
(Editing by Vicki Allen)