TRAVERSE CITY, Mich. \u2014 Invasive grass carp have reached three of the Great Lakes and pose a significant environmental risk there, but time remains to prevent them from getting out of hand, according to a scientific analysis released Friday.
The voracious grass carp is among four Asian carp species threatening to reach the world\u2019s largest surface freshwater system. Bighead and silver carp, the most feared, would compete with native fish that eat microscopic plants and animals, while grass carp feast on aquatic vegetation that provides crucial habitat and spawning grounds.
Grass carp have been found in Lakes Erie, Michigan and Ontario, although it\u2019s uncertain how many there are or how widely they have spread, researchers said. At least some are reproducing.
\u201cFor the first time, we have a binational, peer-reviewed study by some of the best minds and practitioners in the field who have a consensus on what the risk is to the Great Lakes from grass carp, and it\u2019s pretty substantial,\u201d said Marc Gaden, spokesman for the Great Lakes Fishery Commission.
Grass carp were introduced to the U. S. in the early 1960s to control weed growth in waterways. Like other Asian carp, some escaped into the Mississippi River and have migrated north toward the Great Lakes.
It has long been known that at least a small number of grass carp were in the lakes, Gaden said. Some may have slipped into Lake Michigan through a Chicago-area waterway network before electric barriers were erected to block fish migration. People might have released others, intentionally or by accident.
\u201cThey\u2019ve just been humming in the background,\u201d Gaden said. \u201cThey haven\u2019t gotten a lot of attention. Once in a while one would get captured.\u201d
But they have turned up more often in recent years and the threat of a full-fledged invasion appears to be rising, he said. A particularly ominous sign is that some of those caught have been fertile. Grass carp reared in hatcheries, which some states allow, are supposed to be sterilized before being released.
Twenty-three grass carp have been caught in Canada since 2012, including five in Lake Ontario at Toronto, said Becky Cudmore, Asian carp program manager for Canada\u2019s fisheries and oceans agency and the report\u2019s primary author.
\u201cRight now, the sterile fish outnumber the fertile fish,\u201d Cudmore said. \u201cThis isn\u2019t game over, but we are finding more of these fertile fish.\u201d
The analysis said it is \u201cvery likely\u201d that grass carp will become established in Lakes Erie, Huron, Michigan and Ontario within 10 years unless effective steps are taken to stop them. The risk is lower in frigid Lake Superior, which offers less food.
An established population is one that reproduces over multiple generations.
Researchers are studying how to prevent that, Gaden said. Tougher enforcement of laws against bringing them into the region would help, along with greater care to prevent release of fertile fish from hatcheries.
Another possibility would be using nets to block their path to spawning areas during times when they reproduce, Cudmore said. Asian carp are known to spawn later than native fish.
\u201cOur assessment is saying that yes, they were showing up before, but now they\u2019re starting the invasion process,\u201d she said. \u201cThey have arrived. Now is the time to act.\u201d
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