By Dan Egan of the Journal Sentinel
July 12, 2012
For seven years, reporter Dan Egan has been reporting on threats facing the lakes. His groundbreaking work has shown the damage caused by invasive species and has laid out the bold steps that could be taken to restore and protect the world’s largest freshwater system. Section | Blog
Biologists disagree over the threat Asian carp pose to the Great Lakes. Some believe the jumbo fish won’t thrive because the zebra and quagga mussels have already stripped from the lakes the plankton that the invasive fish depend upon.
But a new study released Thursday by the U.S. and Canadian governments says two species of Asian carp – bighead and silver – “pose a substantial risk to the Great Lakes if they become established.”
The peer-reviewed report, 16 months in the making, was led by Fisheries and Oceans Canada and drew on work from scientists from both sides of the border.
“This Asian carp risk assessment is sobering,” said Michael Hansen, the Great Lakes Fishery Commission’s vice chairman.
“It concludes that arrival of Asian carps is looming, and should the fish become established in the Great Lakes, that their effects on the ecosystem would be severe.”
The only barrier between the bighead and silver carp and Lake Michigan is an electric fish barrier on the Chicago Sanitary and Ship Canal, about 30 miles downstream from the Chicago lakeshore. To date, only one bighead carp has been found above the barrier, though water samples taken since 2009 have shown traces of bighead and silver carp above the barrier.
Soon after the first DNA samples were found above the barrier in late 2009, federal officials said it was a concern but stressed that an invasion was not imminent just because a handful of fish may have made it into the Great Lakes basin. The deputy regional director of the U.S. Fish and Wildlife Service said at the time that it would likely take several hundred fish to make it into Lake Michigan to establish a breeding population.
The new report contradicts that statement. It says as few as 20 fish – 10 females and 10 males – could launch an invasion.
Some ecologists contend that plankton populations have been so reduced by the filter-feeding quagga and zebra mussels that bighead and silver carp would find little to eat, though many believe the fish could still find a home in the lakes’ shallow, warm bays and harbors – places that sport fish, as well as the humans who chase them, tend to congregate.
Hansen said the latest science tells a different story.
“The Great Lakes contain ample food for Asian carps and ample spawning habitat, making their spread highly likely, even into comparatively less-hospitable places like Lake Superior,” he said.
Silver and bighead carp were imported by Southern fish farmers decades ago and were initially used to keep catfish ponds clean. They were also used in sewage treatment experiments. They quickly escaped from their containment ponds and have been migrating northward since.
The Fishery Commission and several of Illinois’ neighboring states want the federal government to plug the canal and re-establish the natural divide between the Great Lakes and Mississippi River that was destroyed when the canal opened more than a century ago.
There are other pathways for the carp to make the jump from the Mississippi basin, but by far the biggest threat to the lakes is the canal.
“We must support every effort to keep bighead and silver carps and other invasive species out of the Great Lakes,” Hansen said. “Invasive species threaten the $7 billion fishery, and they hurt the economy by undermining tourism, jobs and prosperity.”