Aquatic Invasive Species

Aquatic invasive species (AIS) include plants and animals that spend most or all of their lives in the water. There are three aquatic invasive species known to occur within the Arrowhead region of Minnesota, the rusty crayfish, spiny waterflea and zebra mussel.

For a complete list of Minnesota’s infested waters, click here.

Cook and Lake Counties have created an aquatic invasive species prevention plan that outlines the efforts that the counties will undertake to help prevent the spread of harmful AIS within its boundaries.

Cook County’s AIS Prevention Plan
Lake County’s AIS Prevention Plan

Rusty crayfish (Orconectes rusticus)

Native to: Ohio River basin
Identification: Identifying crayfish is difficult. Rusty crayfish have more robust claws, larger than any native species to the arrowhead. Rusty crayfish claws have a black tip that other species lack. Rusty crayfish also have two rusty spots on other side of the carapace. However, these spots may not always be present. Especially if hybridization has occurred.

Credit: Sheri Snowbank UW-extension St. Croix basin

Impacts: The destruction of aquatic plant beds is the most serious impact, especially in unproductive northern lakes of the Arrowhead. Submerged aquatic plants are important for habitat, shelter, nest areas, and erosion control.
Although native crayfish eat aquatic plants, rusty crayfish eat even more because they have a higher metabolic rate and appetite. They also grow larger, hide less often from predators – and therefore feed longer – attaining high population densities.

Rusty Crayfish
credit – MN Sea Grant

This aggressive species often displaces native crayfish species through 3 primary mechanisms:

1) Crayfish-to-crayfish competition
Rusty crayfish are better able to exclude other crayfish from shelters and better able to compete for limited food resources.

2) Increased fish predation
Rusty crayfish can increase fish predation on native crayfish by forcing native species from the best hiding places. Native crayfish swim away from attacks by fish or rustys making them vulnerable prey. Rusty crayfish, on the other hand, assume a claws-up defensive posture that reduces their susceptibility to fish predation. Also, rusty crayfish are larger and have larger claws than most native species, which results in fish preying upon native species over rusty crayfish.

3) Hybridization
Rustys hybridize with Orconectes propinquus. This hybridization results in fertile and vigorous offspring, but ultimately results in the decline of Orconectes propinquus. The competitive superiority of the hybrids helps exclude genetically pure Orconectes propinquus faster than Orconectes rusticus would without hybridization.

Control: Ways to eradicate rusty crayfish have not been developed, and none are likely. Harvesting helps minimize their impacts.

Cook County Rusty Crayfish Map
Lake County Rusty Crayfish Map

Click here to learn more

Spiny water flea (Bythotrephes longimanus)

Native to: Europe and Asia

General Characteristics

Spiny waterfleas collected in mass on fishing line

Disrupting the balance
Spiny water fleas eat zooplankton that are also important food for juvenile fish. Because of the rapid reproduction rate of spiny water fleas their population is able to monopolize the zooplankton food supply.

Credit Emily DeBolt – Lake George NY

 Clean, Drain, Dry your gear to stop hitchhiking

Cook County Spiny Waterflea Map
Lake County Spiny Waterflea Map
Click here to learn more

Zebra mussel

Native to: the Black, Caspian, and Azov Seas in eastern Europe

Zebra mussels attached to a native mussel

There are currently no known populations of zebra mussels in Cook County, MN.
Lake County Zebra Mussel Map
Click here to learn more

Chinese mystery snail (Cipangopaludina chinensis)

Native to:  Asia

Mystery snails form dense populations and out compete native species for food and habitat. Mystery snails are intermediate hosts for parasitic worms that can kill waterfowl when transmitted. Shells litter shorelines and clog water intakes.

They are typically spread by aquarium dumping and can survive out of water for days by closing their ‘trap door’ shell. It is nearly impossible to eradicate mystery snails making your actions vital in preventing their spread.

Questions about aquatic invasive species in the Arrowhead?

In Cook County, contact Amanda Weberg:                                                                                                                     218-387-2792.

In Lake County, contact Derrick Passe:                                                                                                         218-834-8575.