TRAVERSE CITY, Mich. -- Live Asian carp don't necessarily have to be present for their DNA to turn up in the environment, according to a government study released Wednesday that could intensify the debate over how to prevent the aggressive, hungry invaders from reaching the Great Lakes and other vulnerable waters.
DNA is found in excrement, slime and scales from live fish. But the report by three federal agencies identifies six other possible means through which genetic fingerprints from bighead and silver carp could find their way into locations such as the Chicago waterway system and western Lake Erie, where it has been detected in dozens of samples taken in recent years.
Those potential pathways include storm sewers, fisheries sampling gear, fish-eating birds, dead fish carcasses, barges and sediments, the U.S. Army Corps of Engineers said in a statement accompanying the report. It said carp DNA attached to any of those sources could remain for days before disintegrating.
Scientists with the corps, the U.S. Fish and Wildlife Service and the U.S. Geological Survey are conducting a three-year study designed to answer questions raised by the repeated discovery of Asian carp DNA in rivers and canals in the Chicago area -- including locations beyond an electric barrier intended to block the carp's northward march toward Lake Michigan. Their DNA also has been found in the Mississippi River beyond Minneapolis.
"The purpose ... is to improve the understanding and interpretation of Asian carp environmental DNA results, so we can refine and make this relatively young monitoring tool the most effective to detect live Asian carp presence," said Kelly Baerwaldt, an Army corps fisheries biologist and Asian carp program manager. Additional reports are planned as the study continues.
Bighead and silver carp escaped into the Mississippi River from sewage treatment ponds and fish farms in the Deep South decades ago and have migrated northward, invading numerous tributary rivers. The filter feeders gobble massive volumes of plankton -- microscopic plants and animals crucial to aquatic food webs.
Scientists say if allowed to infest the Great Lakes, the carp eventually could crowd out native species, endangering the region's $7 billion fishing industry. Silver carp, which spring from the water when startled and have collided jarringly with boaters, pose a threat to tourism.
Some state and local officials in the Great Lakes region want structures placed in the Chicago waterways to seal off Lake Michigan from the Mississippi watershed. Business and government leaders in Chicago say that would devastate shipping in the area, and some have questioned whether the DNA findings are sufficient evidence that the carp have evaded the electric barrier.
Just one live carp has been found beyond the barrier network, which is in a canal 37 miles southwest of the city.