Hey Spence, sorry it took me a while to get back to you on your question of the native lampreys. According to Dr. Miehls, it is the SIZE of the parasite relative to it's host that is the problem. In the ocean, sea lampreys parasitize larger fish like tuna, mackerel, billfish, etc. and are too small to actually do any harm to their hosts, other than leaving an itchy spot! (I just noticed that I can STILL see the leech bite on my leg I got on the Pine back in August...) Now, they grow bigger in the ocean, like up to 2 1/2 feet long, but still considering the size of their hosts they don't really cause much of a problem. Despite the fact that they don't get that big in the Great Lakes (specimens above are average-sized), they are still MUCH larger in terms of size compared to their newfound hosts, e.g., lake trout. She said, "Imagine a parasite the size of a BASEBALL BAT hanging off of you, sucking your blood. You wouldn't live very long, would you??"
So, the native lampreys are just little guys, and only the silver and chestnut are parasitic. They don't kill their hosts either, because they EVOLVED with them, the problem with the sea lamprey being INVASIVE. Brook lampreys don't feed as adults at all, they simply live for about a month, long enough to mate, lay eggs, and die. And they ARE actually kind of cute, I shocked up a lot of western brook lampreys when I worked at South Slough Reserve on the Oregon coast.
Classic lesson about the harm invasives can do.
Jonathon
No matter how big the one you just caught is, there's always a bigger one out there somewhere...