Invasive signal crayfish found in Minnesota lake for first time

The Minnesota Department of Natural Resources has confirmed the presence of signal crayfish, an invasive non-native species, in Lake Winona, adjacent to Alexandria in Douglas County. This is the first confirmation of signal crayfish in Minnesota waters.

A commercial harvester contacted the DNR after trapping two signal crayfish in Lake Winona. Since the first catch, the harvester has found eight additional signal crayfish in Lake Winona. The DNR followed up with trapping in Lake Winona and in two adjacent connected lakes but did not capture additional signal crayfish.

One female was among the 10 adult signal crayfish captured and removed from Lake Winona. At this time, there is no evidence of reproduction; no eggs or juveniles have been found.

Signal crayfish are larger and more aggressive than Minnesota crayfish and the invasive rusty crayfish. They eat aquatic plants, detritus, fish eggs, smaller crayfish species and other beneficial native invertebrates. Signal crayfish might outcompete native species for food and habitat. Signal crayfish can spread between connected waterways or be transported by people. They can also crawl over land at night and during wet weather.

“Importing live, non-native crayfish to Minnesota is illegal without a permit,” DNR Aquatic Invertebrate Biologist Don Eaton said. “Regardless of species, it is illegal to release non-native plants or animals into the environment. We deeply appreciate that people harvesting crayfish are keeping a close watch on their catch and that, in this case, the harvester quickly reported this unusual-looking crayfish to the DNR.”

Signal crayfish are bluish-brown to reddish-brown in color, with large, smooth claws and a smooth carapace – the protective covering over their head and mid-section. They have a white or pale blue-green patch near their claw hinge, which looks like a signal flag.

People who think they might have observed signal crayfish or other invasive species should note the exact location, take photos, keep the specimen, and submit their observations to EDDMapS or their local invasive species specialist. To help confirm sightings of signal crayfish, photos of the blue-green patches on claws, the bright red coloring on the underside of the claws and full-body views from above and below are ideal. Placing the crayfish next to a ruler or other size reference is also helpful.

The DNR website has information about signal crayfish and about pathways by which non-native, prohibited and invasive species are typically introduced.