Rusty crayfish: An invasive menace

While walking on frozen Birch Lake recently I saw something I had never seen before. An ice angler ran to a tip-up displaying a flag and pulled up not a walleye but a crayfish. It was a rusty crayfish, a species native to the Ohio River valley that anglers brought to Wisconsin as bait and that has taken over a goodly number of lakes.

I thought crayfish just lay dormant all winter, but apparently not. At any rate, the rusties overran Birch Lake about 15 years ago, wiping out its rich cabbage weed beds and changing the whole structure of the fish population. Panfish and perch are all but gone, although walleyes are abundant and smallmouth bass reach genuine trophy size.

A trapping program run by the Friends of Birch Lake group has helped bring the crayfish population under control. So has increasing predation by fish and, at least according to rumor, so has a viral disease. Still, it’s upsetting to see such profound change brought on by a species that does not belong in the lake.

Invasive species – fish, plant, invertebrate – threaten many inland lakes, maybe including yours. If you want to learn about just how rusty crayfish can affect a lake, you can read my 2008 story from Wisconsin Natural Resources magazine at http://dnr.wi.gov/wnrmag/html/stories/2008/oct08/crayfish.htm.