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Harmful Aquatic Hitchhikers: Crustaceans: Rusty Crayfish

What does a rusty crayfish look like?
Minnesota Sea Grant
Minnesota Sea Grant
Click image to enlarge
  • Rusty crayfish can be identified by their robust claws, and by dark, rusty spots on each side of their carapace. The spots are located on the carapace as though you picked up the crayfish with paint on your forefinger and thumb. The spots may not always be present or well developed on rusty crayfish from some waters.
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Why is the rusty crayfish considered to be a nuisance?
  • Competition with Native Species - Being an aggressive species, the rusty crayfish often displaces native or existing crayfish species. Ultimately, this could result in less food for fish. Crayfish are eaten by fish, but because of their thick shell relative to their soft tissue, the food quality is not as high as many of the invertebrates that they replace. Less food or lower food quality means slower growth, which can reduce fish survival.
  • Destruction of aquatic plant beds - When introduced, rusty crayfish reduce aquatic plant abundance and species diversity. This can be especially damaging in relatively unproductive northern lakes, where beds of aquatic plants are not abundant. Submerged aquatic plants are important in these systems for habitat for invertebrates (which provide food for fish and ducks), shelter for young gamefish, or forage species of fish, nesting areas for fish, and erosion control (by minimizing waves).
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How do rusty crayfish affect recreational users?
  • Anglers - When rusty crayfish are introduced to a new system, the impacts are potentially devastating. However, because of the nature of these impacts, it takes time for anglers to directly feel these results. When a plant bed's diversity is decreased, a variety of effects take place. Generally, many species have difficulty acquiring food, which is necessary to grow and reproduce. Eventually, certain species decline, which ultimately disrupts the larger food web and effects all the species in an ecosystem including gamefish.
  • SCUBA Divers - Part of the lure of SCUBA diving is seeing life underwater. With the introduction of rusty crayfish, the benefit of seeing the diversity of underwater life will decrease.
  • Swimmers - In the heavily-infested northern Wisconsin and Minnesota lakes, recreational swimming has been affected because large numbers of rusty crayfish now occupy favorite swimming holes. The fear of stepping on and getting pinched by the large-clawed "rusties" is very real.
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Where is the rusty crayfish currently found?
USGS/Florida Caribbean Science Center
USGS/Florida Caribbean Science Center
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  • Rusty crayfish are thought to be native to the Ohio River Basin, particularly throughout the states of Ohio, Kentucky, Tennessee, Indiana, and Illinois. But, now rusty crayfish are also found in Michigan, Massachusetts, Missouri, Iowa, Minnesota, New Mexico, New York, New Jersey, Pennsylvania, Wisconsin, all New England states except Rhode Island, and many areas in Ontario, Canada.
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What is the rusty crayfish's potential to spread elsewhere in U.S.?
  • Experts are concerned about the rusty crayfish's ability to spread for two reasons:
    • It is believed that anglers using rusty crayfish as bait introduced these hitchhikers outside of their original range.
    • Rusty crayfish can live in a variety of waters including lakes, rivers, ponds, and streams with adequate rock, log, and debris cover. They prefer substrates of clay, silt and gravel, and are most active from spring to fall when temperatures are above 8C.
Short term benefits of the rusty crayfish don't override long term impacts
  • While some anglers may find that rusty crayfish are an effective bait, use of them outside their traditional range can have drastic results. If anglers use rusty crayfish, you need to confine this use to the states of the Ohio River Basin.
How can I prevent the spread of rusty crayfish?
  • Specifics to prevent the spread of species.
    • Become knowledgeable about the crayfish native to your area,
    • Be able to identify the rusty crayfish
    • Do not release live bait into any waters.
What else can I do?
References
  • (Gunderson, Jeffrey. (1998). Rusty Crayfish - A Nasty Invader. http://www.d.umn.edu/seagr/areas/aqua/rusty.html (6 January 2000).
  • Ontario Federation of Anglers and Hunters. (1999). Rusty Crayfish. Available: http://www.ofah.org/rusty.htm (2 December 1999).
  • Michigan Department of Natural Resources. (1997). Spotting Scope. Available: http://www.dnr.state.mi.us/wildlife/species/default.htm (18 December 1999).
  • USGS/Florida Caribbean Science Center, www.fcsc.usgs.gov

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