The U.S. Army Corps of Engineers announced Friday it will turn up the power on its electric fish barrier on the Chicago Sanitary and Ship Canal to keep Asian carp from migrating into Lake Michigan.
The agency acknowledged this spring that lab studies revealed the barrier was not operating at a strength high enough to repel small fish, but officials at the time said they had no plans to turn up the electricity because they did not believe small fish were in the vicinity of the barrier.
Maj. Gen. John Peabody said Friday his agency had no new information that little fish were approaching the barrier, but "our safety testing told us we can (turn up the barrier) without any additional safety risks."
The worry is that the barrier could send sparks between barges traveling the canal, some of which carry flammable materials. But Peabody said the research showed there was no increased risk in turning up the voltage, provided the agency run only one of its two permanent barriers at a time.
Peabody said the agency never intended to operate those two barriers simultaneously, but said a third weaker barrier that is just upstream from the new barriers will continue to operate around the clock to provide redundancy.
The Army Corps released a separate study Friday that essentially validates the use of "environmental" DNA sampling to get a better idea of where the fish may be lurking.
To date, only one actual Asian carp has been plucked from waters above the barrier, but water samples taken above the barrier have consistently tested positive for Asian carp DNA.
An independent peer review said that the DNA sampling is a valid tool in the effort to figure out if the carp have advanced into Lake Michigan, though Peabody said the sampling still has big limitations.
"We think it's very effective for detecting the genetic presence of Asian carp, but it cannot confirm at this stage . . . whether it came from a live fish, a dead fish, fish parts, what have you."
Some have speculated that the genetic material picked up in the water sampling came not from live fish, but perhaps from bilge discharges from barges, or from bird droppings or sewage discharges.
"There is not evidence those things happen frequently enough to be major explanations for the patterns (of DNA detection) we are seeing in the canals," said David Lodge, a biologist and Great Lakes expert at the University of Notre Dame.
Lodge and other scientists who pioneered the technology at Notre Dame say the DNA has been picked up in so many different areas of the canal system that the only plausible explanation is that Asian carp are indeed above the barrier.
But they acknowledge a positive sample cannot indicate the number of fish, or whether they are of breeding age.
The Army Corps' new report encourages refining the technology so it can do a better job of estimating actual fish numbers in areas that test positive for DNA, which researchers are already pursuing.
The Army Corps also reported Friday that ongoing telemetry studies show that the barrier is repelling fish.