The number of sea lamprey in Lake Michigan shot up again last year. The fight against the parasite is 50 years old, but lately the lamprey has been getting the upper hand. Its population has been on the rise for a decade, and is now estimated to be about 50 percent higher than fishery biologists would like.
A new study estimates there are about 90,000 adult lamprey in Lake Michigan. Lake managers would like there to be less than 60,000. Still it's better than 2007, when the number was close to three times the target.
Lamprey are the oldest invasive species in the Great Lakes. The parasite attaches to large fish such as salmon and lake trout and is one of the main reasons trout are doing so poorly in Lake Michigan.
Jeff Slade, who directs the lamprey control program for the U.S. Fish and Wildlife Service, says they've brought the numbers down a lot from two years ago.
"I think we're just having a hard time to getting them where we want them to be. Remember these are pretty low levels that were trying to achieve," he says.
Fish and Wildlife controls lampreys by dumping poison into rivers. One of the problems recently has been lamprey breeding in the Manistique River in the Upper Peninsula, one of the largest watersheds in Michigan. An old dam there had allowed the invader to swim upstream and reproduce by the millions. The U.S. Army Corps of Engineers is supposed to build a barrier on the Manistique next year.
Lamprey numbers are also high in Lake Huron because of breeding in the St. Mary's River.