Most likely they are the "Silver Lamprey" which are a natural organism found in the Great Lakes. They are not the problem that the Sea Lamprey is.
We have talked about the Silver Lamprey here a few times and one of the better web sites on this little critter is here:
Lampreys of Michigan
They talk about the Silver about 1/2 way down. Do a search on your favorite search engine using the name Silver Lamprey as the exact phrase.
BTW, I have caught at least one Walleye with one or more on them this year. And, a couple have had small wounds which I figure were Lamprey. I did find a Sea Lamprey last year on a large carp.