by Alisha Davidson, Ph.D.
ML&SA Research and Development Coordinator
For many Michigan riparians, crayfish hold a unique and often sentimental place amongst lake fauna. As the largest crustaceans in Michigan inland lakes, these animals are highly visible (and easily caught by kids with a bit of finesse and a snorkel). Most lake users would be familiar with the northern clearwater crayfish (Orconectes propinquus) or virile crayfish (Orconectes virilis), the two most common species. Other natives include the calico crayfish (Orconectes immunis), the digger crayfish (Fallicambarus fodiens), the devil crayfish (Cambarus diogenes), painted hand mudbug (Cambarus polychromatus), white river crayfish (Procambarus acutus) and the big water crayfish (Cambarus robustus). These native species play an important role in the ecosystem as prey species for fish and predators of snails and other aquatic insects and plants.
Unfortunately, Michigan inland lakes are threatened with several invasive crayfish species. The rusty crayfish (Orconectes rusticus) is already a common invasive in Michigan waters. Rusty crayfish are native to Ohio and Kentucky, but have spread to several Great Lakes states and beyond. They have been (and continue to be) transferred to and around Michigan in two ways. First, anglers use them as bait and accidently release or intentionally dump them overboard at the end of a day’s fishing. Second, hobbyists stock them in their aquaria and release them into the “wild” when they outgrow their tanks. This species is restricted in Michigan – possession of this specie is illegal except for purposes of destroying them for consumption, fertilizer or trash. For more information on this species, visit the rusty crayfish fact sheet at nas.er.usgs.gov for this species.
Another invasive is the red swamp crayfish. This species is native to the southern US and highly aggressive. It has already invaded Illinois, Wisconsin and Ohio (as well as overseas in Europe) through the same means as the rusty crayfish. The red swamp crayfish can tolerate a variety of environmental conditions; notably, it can withstand dry periods of up to four months and can walk several miles over land in search of a water source. In June 2015, several red swamp crayfish were found in a bait dump at a Holland city park. Concerned that live individuals may have made it into nearby waters, the Michigan Department of Natural Resources (DNR) sampled for this species in Lake Macatawa but luckily found no live individuals. As of September 2015, the red swamp crayfish is considered not present in any Michigan waters. Sale or possession of this species is prohibited in Michigan. For more information on this species, visit the red swamp crayfish fact sheet at nas.er.usgs.gov for this species.
Both species can displace native crayfish populations due to increased aggression, size and growth rate. Rusty crayfish can also hybridize with the northern clearwater crayfish; the hybrids are more vigorous than the pure northern clearwater populations so out compete and displace them. Both species can also reduce the size and diversity of aquatic plant beds, which are important for providing nest sites and habitat for fish, food for fish and ducks, and erosion control through wave minimization. They also cause the decline of game fish such as bass, bluegill and northern bike through consumption of fish eggs and competition with fish for food. Even fish that protect their nests from predation like bass and bluegill may not be able to defend their nests from these aggressive invasive crayfish. Red swamp crayfish can even eat adult fish and amphibians. For homeowners, the red swamp crayfish is a particular nuisance because its burrows can decrease shoreline stability and increase erosion. In southeast Wisconsin, they have caused significant damage with high control costs.
No eradication methods have yet been found for either the rusty or red swamp crayfish – so once introduced, these invasive crayfish species are here to stay. Important actions to preventing these species from arriving and spreading throughout Michigan include: learn how to identify both the rusty and red swamp crayfish (see pictures) and NEVER use or release these species in the wild (land or water). Finally, the DNR is asking anyone who thinks they have found a red swamp crayfish — dead or alive — or have seen someone using them as bait, to call the Report-All-Poaching hotline at 1-800-292-7800.
Click on individual images below for full size photo of each crayfish represented in gallery.