Illinois Natural History Survey - University of Illinois

Introduced Crayfishes in Illinois

The practice of introducing nonnative plants and animals into new areas for food production and sport and as pets has occurred commonly throughout human history. While many of these introductions go unnoticed or cause little harm to our natural resources, some cause severe problems for the native organisms that live in areas where introductions occur.

In Illinois, the introductions of aquatic species, such as the common carp, grass carp, and zebra mussel, have drastically affected our streams, rivers, and lakes. One of the newest threats to our native aquatic plants and animals are crayfishes. Field work conducted by Illinois Natural History Survey (INHS) biologists has documented that the rusty crayfish, a non-native species first collected from Illinois in 1973, has rapidly expanded its range in the state and that a second non-native species has recently become established in the state. Crayfishes, also known as crawfish or crawdads, are found in almost all aquatic habitats in Illinois including lakes, creeks, rivers, and swamps. By feeding on plant material, insects, and snails, and by being a favorite food item for sportfishes, such as basses and sunfish, crayfish function as important members of aquatic food webs. The appetites of sportfishes for crayfishes have led to the introduction of non-native species. When fishermen use crayfishes as bait, they often dump unused crayfishes into lakes and rivers at the end of the day. This practice has most likely led to the establishment and rapid spread of the rusty crayfish (Orconectes rusticus) in Illinois. The rusty crayfish was first collected in Illinois in 1973 from the Illinois River at Peoria, and until 1985 was known from only nine locations. Since then the species has spread throughout the northern half of Illinois and can be found in almost all the major rivers in that part of the state. A field study conducted from June 1994 to October 1995 found the rusty crayfish at 39 sites in Illinois, 24 of which were in or near areas that receive intense recreational fishing pressure.

A rusty crayfish, Orconectes rusticus, from northern Illinois. The rusty colored spots on the side of the crayfish distinguish this species from all other crayfishes in Illinois. (Photo by Christopher Taylor and Kevin Cummings, INHS Center for Biodiversity.)

Researchers at INHS and other institutions have documented the effects rusty crayfish have on aquatic ecosystems. The most dramatic effect is the displacement of native crayfish species. Prior to the appearance of rusty crayfish, the virile crayfish (Orconectes virilis) and the northern clearwater crayfish (Orconectes propinquus) occurred commonly in northern Illinois' lakes, creeks, and rivers. In areas where rusty crayfish are now found, both the virile and northern clearwater crayfish are either present in very small numbers or totally absent. The rusty crayfish is a large, aggressive species compared to other Illinois crayfishes and as such is able to force these other species out of habitats that provide refuge from predation. Deprived of these habitats, species such as the virile and northern clearwater crayfishes are either consumed by fish or mammal predators or are forced to move to other areas. Researchers outside of the Survey have shown that rusty crayfish can affect other members of the aquatic food chain by rapidly expanding their population sizes after moving into new habitats. These large populations can, over time, consume most of the aquatic vegetation used for refuge from predation by juvenile fishes.

The golden crayfish, Orconenctes lutens, a recent introduction into Illinois waters. (Photo by Christopher Taylor and Kevin Cummings, INHS Center for Biodiversity.)

In recent field work, INHS biologists discovered a population of a second non-native crayfish species in Illinois. The golden crayfish (Orconectes luteus), a species that occurs natively in central and southern Missouri, was first collected in Illinois in 1992. Subsequent work has shown that a reproducing population of the golden crayfish occurs in a restricted portion of Apple Creek in Greene County and that displacement of native species is not apparent. In an effort to determine if rusty crayfish are unique in their ability to outcompete native crayfishes, future work will focus on determining if the golden crayfish is able to displace other species.

Current Illinois law prohibits the possession and sale of live rusty crayfish. Its strict enforcement represents the only means currently known to slow the spread of the rusty crayfish. Native Illinois crayfishes, especially our rare and endangered species, can ill afford to be forced from native habitat by foreign invaders.

Christopher A. Taylor, Center for Biodiversity

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