How is an aggressive invasive crayfish affecting native species?

  • Rusty Crayfish, Photo Credit: Jeff Gunderson, MN Sea Grant

    © Jeff-Gunderson, Minnesota Sea Grant

  • Lake Superior Reserve research interns research crusty crayfish populations on St. Louis River
  • research students collect data and crayfish traps
  • St. Louis River


The rusty crayfish, Orconectes rusticus, is an aggressive species of crayfish native to the Ohio River basin that is invading rivers and lakes in the Upper Midwest, including Wisconsin and Minnesota. The rusty crayfish outcompetes native species and has replaced other species in many of Wisconsin’s watersheds, impacting native vegetation and food webs.

Like many Wisconsin and Minnesota waterways, the St. Louis River Estuary is home to the invasive rusty crayfish, which was first documented here in 1999. One of our ongoing research projects is documenting the rusty crayfish population in the estuary, as well as the populations of native crayfish.

So far, our research has shown that populations of all crayfish in the estuary, including rusty crayfish, have plummeted since 1999. This makes us wonder: What is behind this crash in crayfish populations? Did a large 2012 flood that wreaked havoc on many native species also affect crayfish? Or are there more smallmouth bass in the estuary feasting on them? Or could pollution or a parasite be responsible? Dissections of the crayfish we have caught in recent years show high numbers of the parasite Microphallus sp. present in their bodies. Still, there are many potential reasons for the crayfish population collapse.

We’re exploring these questions as we continue research into crayfish populations in the future.