Photographer:U.S. Geological Survey Archive Affiliation: U.S. Geological Survey Source: www.bugwood.org Copyright: CC BY-NC 3.0
This crayfish has large claws that are smooth and have black tips. Color varies from gray-green to reddish brown. The most distinctive feature is a pair of dark-red or rusty spots on either side of the carapace just in front of the tail; however, these spots are not always present. Maximum length of the body without the claws is about 4in and males are larger than females.
The rusty crayfish is very aggressive and displace native crayfish from shelter and compete with them for food sources. When the smaller native species are forced from their hiding places, they become more vulnerable to predators and declines of native crayfish have occurred in the lakes of Wisconsin. The high metabolic weight of Orconectes rusticus means it consumes a lot of food for its size destroying submerged vegetation that provides shelter for other invertebrates and young game fish. Also, they may directly harm native fish by eating their eggs and reducing the amount of invertebrate prey upon which the juvenile fish depend on. When rusty crayfish invade declines of larval mayflies, midges and stoneflies occur; along with fish species like bluegill, pumpkinseed, smallmouth bass, largemouth bass, lake trout, walleye and northern pike, making this crayfish a very unwelcomed guest.
Orconectes rusticus consumes anything from aquatic plants to bottom-dwelling invertebrates such as worms, snails and bivalves but they are also known to eat fish eggs and small fish. The rust crayfish mates in late summer and early fall. Fertilization is external when a male crayfish transfers his sperm to the female in a seminal receptacle that he places on her belly; then the female will release eggs completing the process. Females can produce 80-575 eggs and it takes 3-6 weeks for the eggs to hatch. The young continue to hold onto their mother’s swimmerets for several weeks as they go through 3-4 molts. After the young leave the female, they undergo 8-10 more molts before they become adults. Rusty crayfish live 3-4 years.
It is not clear how Orconectes rusticus got out of its native range in the Ohio River basin. But it is thought that non-resident fishermen brought the crayfish to new areas as bait and released them intentionally or accidentally. Also, this species is popular for school biology classes and is sold by biological supply companies; so releases from classrooms are another way of the rusty crayfish expanding its invasive range. Rusty crayfish are commercially harvested for human consumption, which provides and economic incentive to introduce them to new locations. Since female crayfish store sperm, a single one could start a new population. Their introduction to Wisconsin occurred in the 1960s, southern Minnesota in 1967 and made it over to Maryland in 2007.
Ohio River Basin (Ohio, Kentucky and Indiana)
U.S. Habitat: Freshwater habitats with permanent bodies of water and adequate cover from trees and rocks. They can be found in both still pools and fast-flowing streams. They do not dig deep burrows so they cannot survive when an intermittent stream dries up.
U.S. Present: CO, IA, IL, MI, MN, NC, OR, TN, WI, WV, WY
To manage Orconectes rusticus there are few environmentally sound options. Commercial harvests may reduce numbers and keep the populations in control. Some studies have shown that the over fishing of predatory fishes causes population spikes in the rusty crayfish; by restoring healthy populations of sunfish and bass the impacts of the crayfish can be reduced. The best management practice is to prevent further introductions by educating the public about the threat of this crayfish and the impact it has on freshwater environments.
Olden, J.D., J.M. McCarthy, J.T. Maxted, W.W. Fetzer, and M.J. Vander Zanden. 2006. The rapid spread of rusty crayfish (Orconectes rusticus) with observations on native crayfish declines in Wisconsin (USA) over the past 130 years. Biological Invasions 8:1621-1628.
Olsen, T.M., D.M. Lodge, G.M. Capelli, and R.J. Houlihan. 1991. Mechanisms of impact of an introduced crayfish (Orconectes rusticus) on littoral congeners, snails, and macrophytes. Can. J. Fish. Aquat. Sci. 48(10):1853-1861.
Woodward, Susan L., and Joyce Ann. Quinn. 2011. Rusty Crayfish. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood. 93-94. Print.