New invasive crayfish found in Minnesota lake

a crayfish with claws open
The signal crayfish is a new aquatic invasive species in Minnesota. It was found in Lake Winona near Alexandria, Minn., in September.
Courtesy Minnesota DNR

There’s a new aquatic invasive species in Minnesota. The signal crayfish has been confirmed by the Department of Natural Resources in Lake Winona, near Alexandria, Minn.

Signal crayfish are larger and more aggressive than native Minnesota crayfish and might outcompete native species for food and habitat.

“They can predate fish eggs. They can compete in terms of food items with the fish as well. So lots of potential impacts on the food web of the lake,” said DNR aquatic invertebrate biologist Don Eaton.

The DNR was alerted to the new invasive species by a commercial harvester who immediately notified the agency.

“They realized the importance of the finding and the damage that invasive species can do,” said Eaton. “It’s great to know that there are people out there paying attention to their environment, really super-helpful in terms of trying to slow the spread of invasive species.”

The commercial harvester captured a total of 10 signal crayfish.

a crayfish in a container
The signal crayfish was found this fall in a lake near Alexandria, Minn. It is larger and more aggressive than native crayfish. There is no evidence the crayfish has established a population in Minnesota.
Courtesy Minnesota DNR

The DNR found no signal crayfish in two lakes connected to Lake Winona, and found no evidence of reproduction in the lake. Eaton said surveillance will resume in the spring.

The native habitat of the signal crayfish is generally west of the Rocky Mountains.

It can be imported to Minnesota — with a permit — for use in aquariums, but it is illegal to release in the wild. Officials don’t know how the invasive crayfish got to Lake Winona.

The signal crayfish is on average a couple of inches longer than native crayfish, and three times heavier.

“They have a wide environmental tolerance of different types of conditions,” said Eaton. “So the fact that they’re in the Sierras, they’re in the Cascade Mountains, they’re up in British Columbia — it seems like they would be able to survive in Minnesota lakes.”

The invasive crayfish spreads through connected waterways and human transport. It can also crawl over land at night and during wet weather.

Signal crayfish are bluish-brown to reddish-brown in color, and up to seven inches long from claw to tail. The name comes from a white or pale blue-green patch on their claws that looks like a signal flag.

Anyone who thinks they spot a signal crayfish is asked to record the location, take photos and keep the crayfish.

Suspected sightings of signal crayfish and other invasive species can be reported to the Center for Invasive Species and Ecosystem Health.