Rusty crayfish have been discovered in the Vermillion River in Farmington and Hastings, as well as North Creek in Farmington.

The invasive freshwater crustacean was discovered in Farmington during routine biomonitoring done by the Vermillion River Watershed Joint Powers Organization and the Dakota County Soil and Water Conservation District.

Rusty crayfish are classified by the Minnesota Department of Natural Resources as a regulated invasive species, which means they can be legally bought and sold in the state, but cannot be introduced into public waters, explained Keegan Lund, area invasive species specialist with the DNR.

Rusty crayfish are typically more aggressive than native crayfish, so there is a risk they will harm the existing crayfish population, or breed to create hybrid species. They can also damage fish populations by eating eggs and young fish, damaging native aquatic plants, and preying on other macroinvertebrates like mayflies, midges and scuds.

Despite these risks, Lund said the ecological impact of the rusty crayfish in the watershed will likely be limited and shouldn't affect recreational opportunities like fishing.

"Rusty crayfish are relatively common in the Metro area, and there is some interest in harvesting them for bait or consumption," Lund said.

Anglers with a fishing license can use rusty crayfish to use as bait, but only in the same waterway they were collected from. They can only be sold for bait or aquarium use by a licensed dealer, Lund added.

Monitoring of local bodies of water is typically done by volunteers organized by local Soil and Water Conservation Districts, who then report their findings to the DNR so they can be identified, tracked and mapped.

"Local monitoring is important because we can confirm and record species in Minnesota," Lund said.

The rusty crayfish were discovered by the field biology class from Hastings High School at Vermillion Linear Park. The students were participating in the Vermillion River Watch program. Joe Beattie, the field biology teacher, said he has been taking his class to the location for years.

"Spring and fall every year we monitor the river for macro invertebrates...and this is the first year that we found crayfish that looked different," Beattie said. "There was something different."

The class found what is believed to be five rusty crayfish in the river. The crayfish still need to be confirmed that they are rusty by the DNR.

"Although the simple identifying characteristic is a rusty spot on each side of the crayfish, identification of crayfish can be quite challenging and requires looking at multiple characteristics," Beattie said.

One way Beattie had an inkling that one of his students found a rusty crayfish was from the rusty spot or patch on either side of the thorax.

The students in the class immediately had questions when they heard it was a possibility that the crayfish could be an invasive species. Beattie said they wanted to know how invasive it is, should we be concerned, could there be more, and more questions.

Lindsey Albright, a water resource specialist at Dakota County SWCD, was on site with the students when they found the crayfish. She said she immediately thought it was a rusty because she spotted the red patch on its side. She had also been at the Farmington site when rusty crayfish were found there.

She said she explained the situation to the students who were on site with her in Hastings and said it was a good learning experience for them.

"Obviously, not ideal or good in any way because it is AIS (Aquatic Invasive Species), but because of this, they got to learn about the process of monitoring, identification and reporting an AIS finding," Albright said. "Not something that most students would get to do."

Regulated invasive species as typically less concerning than prohibited invasive species. Examples of regulated species include water hyacinth, goldfish, common carp or the red-eared slider. Prohibited species include zebra mussels, black carp and Eurasian watermilfoil, among many others.

For more information from the DNR on invasive species, visit www.dnr.state.mn.us/invasives/laws.html. For more on the Vermillion River Watershed, visit www.vermillionriverwatershed.org.