The Origin and Distribution of Rusty Crayfish



http://www.seagrant.umn.edu/ais/rustycrayfish_invader

     Rusty crayfish were not found in Wisconsin in a 1932 survey, but populations have rapidly expanded throughout Wisconsin lakes and streams since their introduction around 1960.  Rusty crayfish have been observed in 430 Wisconsin lakes and streams and the occurrence of rusty crayfish in sites that support crayfish has increased from 3% in the 1970s to approximately 50% in 2007.

     The first observation of rusty crayfish in Minnesota was in 1967 at Otter Creek in southern Minnesota. Since then, their range has expanded to approximately 50 different lakes and streams spanning 13 counties.  Rusty crayfish from east central Minnesota  may have resulted from the natural dispersal of introduced populations from Wisconsin. People most likely spread rusty crayfish to the other waters of Minnesota where they are currently found.

     Presumably people can spread crayfish in several ways. Anglers using crayfish as bait are thought to be the primary means of spread. While crayfish never were a significant component of Minnesota live bait sales, they are popular in other states and may have been brought to Minnesota by non-resident anglers.  Rusty crayfish are also sold to schools by biological supply houses. Even though a warning not to release rusty crayfish into the wild accompanies these crayfish, such warnings may be forgotten, or live crayfish may be given away to students. Crayfish from schools or collected from the wild and placed in home aquariums may eventually be released.  Developing a viable commercial harvest of rusty crayfish from natural lakes could be incentive for unscrupulous trappers to plant them into other waters. In fact, this may have contributed to the spread of rusty crayfish in Wisconsin.  The harvest of rusty crayfish for food and bait may provide the only beneficial use for this exotic. Harvest for bait has been going on for over 40 years in Wisconsin. Commercial harvest for food is more recent and varies from year to year in Wisconsin and Minnesota. Regulations in both states make it illegal to introduce rusty crayfish into any waters. In Minnesota, it is illegal to sell live crayfish as bait or as aquarium pets.