1854 Treaty Authority – Impact of Rusty Crayfish on Wild Rice

Note; Lakes included in this research study include Farm, Garden and White Iron.

Orconectes rusticus (rusty crayfish) is the only confirmed species of invasive crayfish in the 1854 Ceded Territory in NE MN. Rusty crawfish prefer rocky substrate, but have been found to inhabit sand, silt, clay, and gravel. They prefer warmer temperatures, but can tolerate cool water and are usually found in shallow areas. Rusty crawfish do not possess an ability to burrow, and require clear and well- oxygenated water to survive.

 Rusty crawfish has been found to graze heavily on germinating aquatic vegetation, and are capable of displacing and reducing the diversity of native aquatic plants (aquatic plants). Introductions of Rusty crawfish have shown detrimental impacts on aquatic plant populations around the littoral zone of lake systems. In some instances, reductions of aquatic plant populations by as much as 80% have occurred.

The 1854 Treaty Authority has interest in the effects of Rusty crawfish on aquatic plant communities that produce native Zizania palustris (wild rice) within the 1854 Ceded Territory. Wild rice is a culturally significant plant that provides sustenance in many forms to the Bois Forte and Grand Portage Chippewa bands. Wild rice typically grows best in shallow depths of 1-3 feet in areas containing soft, organic bottoms. In mid-June, wild rice reaches the “floating-leaf” stage at which point wild rice lays flat on the surface of the water and can form dense leafy mats. In July, wild rice begins to emerge vertically and can stand out of the water up to 6-8 ft. tall. In August and September ripe seed can be harvested or will fall in the water to germinate the next year.

Wild rice populations have been observed to decline in some areas infested with Rusty crawfish, but whether this impact is directly related to an infestation is unknown. The 1854 Treaty Authority conducted a study from 2013 to 2016 testing for the potential impacts of Rusty crawfish on wild rice. From 2013-15 the study focused on if Rusty crawfish negatively impacts wild rice populations, and in 2016 the study addressed the questions of which stages of wild rice growth can Rusty crawfish affect, and if wild rice is a preferred food source.

The full report (16 pages) of the 1854 Treaty Authority wild rice/rusty crayfish project is now available on their web site at:

http://www.1854treatyauthority.org/images/1854-Technical-Report-17-08-Rusty-Crayfish-Report_3.pdf