The Army Corps of Engineers has long contended that its $10 million electric barrier in the Chicago Sanitary and Ship Canal has prevented invasive, voracious Asian carp from getting into Lake Michigan, where many fear they could wreak environmental havoc.
But a year-old study finally released by the Corps on March 24 shows the barrier could indeed be breached by 2- to 3-inch-long baby bighead carp -- one of the breeds of Asian carp already proliferating in waterways linking the Mississippi River and Lake Michigan.
The study was released after the Prairie Rivers Network, represented by NRDC staff attorney Thom Cmar, threatened to sue to enforce a Freedom of Information Act request filed in October. The Corps had previously denied the FOIA request on the grounds the research was in draft form.
Critics say these results are further reason to doubt the electric barrier can really keep Asian carp out of the Great Lakes. Over the past two years "environmental DNA," or eDNA, from Asian carp has been found in multiple locations beyond the barrier, indicating Asian carp have already breached it. Not so, say Army Corps officials, who suggest the eDNA could have gotten there in other ways, like fish released into the lake or with bits of dead fish in the sewer system.
In previous tests by the Illinois Natural History Survey, adult fish dragged through the electrical field in the canal have been completely immobilized by the shock, indicating they could not swim through the 130-foot-long electrical field. Similar tests are currently being conducted wherein fish in cages are subjected to the electric current, and they likewise have all been immobilized by the electricity.
But in tests in tanks and flumes at their Vicksburg, Miss. Laboratory, the company Smith-Root hired by the Army Corps found baby bighead carp could swim through an electrical field at the same voltage as the barrier in the canal. The study found the determined young carp would continue pressing onward even after being "repeatedly immobilized" by the shock. Since small fish have less surface area, they are considered less vulnerable to the effects of electricity in the water.
Cmar said that both the findings and the fact that the Corps was so reluctant to share the year-old results of this study reinforce critics’ contention that the electric barrier is not a viable long-term way to prevent invasive species from moving between Lake Michigan and the Mississippi River.
"They’ve been saying, 'We’re confident our barriers are working,' even as they have these lab results showing small fish are able to cross the barrier," said Cmar.
In a preface explaining the study, Army Corps Major General John W. Peabody and Army Corps colonel Vincent Quarles note the test tank was less than one tenth the size of the electrical field in the Chicago Sanitary and Ship canal, so small fish might have a harder time making it all the way through in the real world, especially if they were to mill around or become fatigued, increasing the time exposed to electricity. The study also suggested a viewing window in the test tank could have provided a haven for fish to recover from the electricity.
Cmar countered that in the canal, fish could likely also find respite from electricity along the sides, or in the wake of passing barges that distort the electrical field.
U.S. Fish and Wildlife Service Midwest deputy director Charles Wooley noted that no baby Asian carp have been found within 116 miles of the barrier. The Smith-Root study says the closest breeding population of Asian carp is in a pool 25 miles away from the barrier, also separated by three locks.
There is disagreement over how far young Asian carp of the sizes tested can swim. Some studies suggest they could swim 25 miles or more; but the Smith-Root study says that would not be likely, especially given that the Asian carp larva drift for at least 100 hours, according to the U.S. Geological Survey, before they mature enough to start swimming. That means they would end up further downstream than they were born, with more distance to swim toward the barrier.
Cmar said even if baby bighead aren’t challenging the barrier right now, the recently released results show that the Corps should not be depending on the barrier to keep Asian carp out. NRDC and other environmental groups have argued that Lake Michigan should be ecologically separated from Chicago waterways to prevent the spread of invasive species.
"They’re putting all their eggs in one basket, which is that they don’t think there are small fish close enough now for it to be a problem," Cmar said. "Why are we relying on these barriers as a solution for the indefinite future when we could be marshaling all our efforts toward getting a real long-term solution in place as soon as possible?"
Photo via Michigan Sea Grant