Taxonomic name: Orconectes rusticus (Girard, 1852)
Synonyms:
Common names: rusty crayfish (English)
Organism type: crustacean Orconectes rusticus (rusty crayfish) are spread by anglers who use them as bait. Orconectes rusticus are prolific and have serious impacts by severely reducing lake and stream vegetation and depriving native fish and their prey of cover and food. Orconectes rusticus also reduce native crayfish populations. Description
According to Bowen (1999), “O. rusticus can be identified by it’s more robust claws and by the 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. In the spring, males will molt into a sexually inactive form (called Form II) and then molt back into the reproductively competent form (Form I) in summer. Form I males are characterized by large claws, a hook on one pair of their legs, and hardened gonapods. The hook and the larger claws are used for grasping females during mating. Males are usually larger than females of the same age.” Similar Species
Orconectes immunis, Orconectes propinquus, Orconectes virilis
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Occurs in:
lakes, water courses Habitat description
According to Bowen (2003), “O. rusticus inhabit lakes, ponds, and streams. They prefer areas that offer rocks, logs, or other debris as cover. Bottom types may be clay, silt, sand, gravel, or rock. Rusty crayfish inhabit both pools and fast water areas of streams. They generally do not dig burrows other than small pockets under rocks and other debris, although there have been reports of more substantial burrows. O. rusticus need permanent lakes or streams that provide suitable water quality year-round.” General impacts
According to Bowen (2003), “invading O. rusticus frequently displace native crayfish, reduce the amount and kinds of aquatic plants and invertebrates, and reduce some fish populations. O. rusticus is an aggressive species”, according to Munjal and Capelli (1982, in Bowen, 2003), “that often displace native or existing crayfish species.” According to Bowen (2003), O. rusticus displaces native crayfish by crayfish-to-crayfish competition and increased fish predation. The reason for increased fish predation on native crayfish is because O. rusticus force the native species from the best daytime hiding places and native crayfish try to swim away from a fish attack instead of taking the more effective claws-up defensive posture the O. rusticus does. Perhaps the most serious impact is the destruction of aquatic plant beds that O. rusticus causes. O. rusticus have been shown to reduce aquatic plant abundance and species diversity which can be especially damaging in areas that are relatively unproductive such as the northern lakes. These aquatic plants are important for habitat for invertebrates, food for fish and ducks, shelter for young game fish, pinfish, or forage species of fish, nesting substrate for fish, and erosion control (by minimizing waves). Although other crayfish eat aquatic plants, O. rusticus eat even more because they have a higher metabolic rate and appetite. O. rusticus, especially juveniles, feed heavily on benthic invertebrates like mayflies, stoneflies, midges, and side-swimmers. So, they are more likely to compete with juvenile game fish and forage species for benthic invertebrates than are native crayfish species. Crayfish are eaten by fish, but because of their thick exoskeleton (shell) relative to soft tissue, their food quality is not as high as many of the invertebrates that they replace. Finally, it has been suggested that rusty crayfish harm fish populations by eating fish eggs. While rusty crayfish have been observed to consume fish eggs under various circumstances according to Horns and Magnuson, (1981, in Bowen, 2003)), there is no scientific study directly linking fishery declines with crayfish egg predation. It's likely that those fish species that lay eggs in relatively warm water (greater than 50° F) are more susceptible to crayfish predation than fish that spawn during colder water periods. No detailed research has been done that proves rusty crayfish cause declines in fish populations. Cabin owners on heavily infested northern Wisconsin and Minnesota lakes have even stopped swimming because large numbers of rusty crayfish occupy their favourite swimming area throughout the day. They fear stepping on them and getting pinched by the large-clawed ‘rustys’.” Uses
"The harvest of rusty crayfish for food and bait may provide the only beneficial use for this exotic" (Bowen, 2003). Geographical range
Native range: Indiana, Ohio, Kentucky, and Michigan in the United States.
Known introduced range: Has invaded many areas surrounding it's native range. It has moved as far west as North and South Dakota, north as Canada and Maine, and south as Tennessee. Introduction pathways to new locations
Other: Anglers using crayfish as bait are thought to be the primary cause of introduction (Bowen, 2003)
Local dispersal methods
Aquaculture (local): Developing a viable commercial harvest of O. rusticus from natural lakes could be incentive for unscrupulous trappers to plant them in other waters (Bowen, 2003).
Escape from confinement: According to Bowen (2003), O. rusticus are sold to schools by biological supply houses. Even though a warning not to release O. rusticus into the wild accompanies crayfish sold to schools, such warnings may be forgotten, or live crayfish may be given away to students and they may eventually be released into the wild.
Other (local): Anglers using crayfish as bait are thought to be the primary cause of introduction (Bowen, 2003) Management information
Preventative measures: Some researchers have suggested that nuisance populations of rusty crayfish are the result of poor fishery management and that by restoring a healthy population of bass and sunfish, O. rusticus would be less disruptive in some lakes. The best method of control is to prevent their introduction. Educating anglers, crayfish trappers, bait dealers, and teachers about the threats posed by O. rusticus will help reduce the risk of spreading O. rusticus to new areas. According to Bowen (2003), “environmentally-sound ways to eradicate or control introduced populations of O. rusticus have not been developed, and none are likely in the near future. The best way to prevent further ecological problems is to prevent or slow their spread into new waters. Regulations in both Minnesota and Wisconsin now make it illegal to introduce O. rusticus into any waters. In Minnesota, it is illegal to sell live crayfish as bait and a Department of Natural Resources permit is required to commercially harvest or culture crayfish.
Physical: Intensive harvest will not eradicate or control crayfish, but may help reduce adult populations and minimize some impacts.”
Chemical: Many chemicals kill crayfish. Some even selectively kill crayfish; however, none are currently registered for crayfish control according to Bills and Marking (1988 in Bowen, 2003). And, none selectively kill O. rusticus without killing other crayfish species. Nutrition
According to Bowen (2003), “O. rusticus feed on a variety of aquatic plants, benthic invertebrates (like aquatic worms, snails, leeches, clams, aquatic insects, and crustaceans like side-swimmers and waterfleas), detritus (decaying plants and animals including associated bacteria and fungi), fish eggs, and small fish.” O. rusticus grow larger, hide less from predators, and attain higher population densities. Therefore they need to feed more. O. rusticus, especially juveniles, feed heavily on benthic invertebrates like mayflies, stoneflies, midges, and side-swimmers. It has been estimated that rusty crayfish might consume twice as much food as similar-sized O. virilis because of their higher metabolic rate. Reproduction
According to Bowen (2003), “mature O. rusticus mate in late summer, early fall, or early spring. The male transfers sperm to the female, which she then stores until her eggs are ready to fertilize, typically in the spring (late April or May) as water temperatures begin to increase. The stored sperm are released as eggs are expelled and external fertilization occurs. The eggs are then attached to the swimmerets on the underside of the crayfish's abdomen ("tail section"). Just prior to egg laying, white patches appear on the underside of the abdomen ("tail section"), especially on the tail fan. These white patches are glair, a mucus-like substance secreted during egg fertilization and attachment. O. rusticus females lay from 80 to 575 eggs. It is important to note that it is not necessary to have both a male and a female crayfish to begin a new infestation. One female carrying viable sperm could begin a new population if released into a suitable environment. Rusty crayfish readily mate in captivity so it is reasonable to expect that mature females, whether used as fishing bait or as science class study specimens, could produce offspring.” Lifecycle stages
According to Bowen (2003), “eggs hatch in three to six weeks, depending on water temperature. Once hatched, young crayfish cling to the female's swimmerets for three to four molts (molting is when crayfish shed their old shell to allow growth). Young crayfish may stay with the female for several weeks. She offers them protection during this vulnerable life stage. Eventually, the young leave the female. They undergo eight to ten molts before they mature, which may occur during the first year, but more likely the following year. Rusty crayfish reach maturity at a total length of one and three-eighths inches and reach a maximum length of about four inches (not including claws). A typical rusty crayfish lives three to four years.” A mature adult male molts twice a year and a female molts once hence why males of the same age are usually larger. Reviewed by: Dr. Brian Hazlett. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor. USA
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
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Last Modified: Monday, 24 January 2005
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