Although native to North America, the rusty crayfish has been introduced to many northern lakes and streams where they cause a variety of problems. It is likely that rusty crayfish were introduced as bait by non-resident fishermen with the first findings in Ontario as early as the 1960s. The rusty crayfish is one of approximately 350 crayfish species that can be found in North American waters. Native crayfish are one of the highest at-risk groups among plants and animals with more than half of the species being either vulnerable, imperiled, critically imperiled or presumed/possibly extinct.

Characteristics

Rusty crayfish have a brown body, and greenish-rusty coloured claws with dark black bands near the tip. The rusty crayfish has more robust clawsand is larger than other native species of crayfish. There are prominent rusty patches on either side of the carapace (which may or may not always be present) as though you picked up the crayfish with rusty paint on your forefinger and thumb. It is on average 10 cm (3.9 inches) in length, not including the claws.

Rusty crayfish will inhabit lakes, rivers, ponds, and streams with adequate rock, log, and debris cover. They prefer bottoms of clay, silt and gravel, and are most active from spring to fall when temperatures are above 8° C. When the rusty crayfish reproduce, they can lay 50-575 eggs at one time.

Rusty crayfish are omnivores so they will eat anything but prefer high protein foods. They feed on aquatic plants, benthic invertebrates (which include aquatic worms, snails, leeches and aquatic insects), decaying plants and animals, fish eggs, and small fish. They have a more aggressive nature than the native species in areas they are introduced to.

Distribution

Rusty crayfish originate from streams in the Ohio, Kentucky, and Tennessee regions. Used as baitfish by anglers, these crayfish have invaded portions of Ontario, Minnesota, Wisconsin, New York, Vermont and Maine. The first Ontario reports of this species were from the Kawartha Lakes in the early 1960s. Since then, rusty crayfish have become established in several areas of the southern and northwestern parts of the province. In the northwest they are found in Lake of the Woods, Quetico Provincial Park, Lake Superior and its tributaries near Thunder Bay. In southern Ontario they are found in the Ottawa River drainage; the upper Mississippi drainage in Lanark and Frontenac counties; the Trent-Severn waterway as far north as Balsam Lake; areas in Haliburton; eastern Toronto region; Berford Lake on the Bruce Peninsula and Eramosa River near Guelph. As this species expands its range naturally and as a result of anglers using it as bait, it is possible that rusty crayfish will continue to spread throughout Ontario lakes and rivers and possibly into the neighbouring provinces of Quebec and Manitoba.

 Download the Rusty Crayfish distribution map

Impact

It is estimated that rusty crayfish can consume twice as much food as native species of the same size due to a higher metabolic rate (Jones & Momot, 1983). Rusty crayfish have a ravenous appetite for aquatic plants; they can degrade aquatic plant beds to the detriment of the aquatic invertebrates and juvenile fish that depend on these areas for habitat. It has been said that what the rusty crayfish does to aquatic plants is the equivalent of clear-cutting forests. Rusty crayfish, especially juveniles, also feed heavily on benthic invertebrates like mayflies, stoneflies, midges, and side-swimmers. By consuming large quantities of benthic invertebrates, fish eggs and young fish, these crayfish could also compete with juvenile game fish and forage fish species for food.

Not only does the rusty crayfish out-compete native crayfish species for food, they also chase them out of the best daytime hiding locations. This makes native populations vulnerable to being eaten by birds and fish. Many fish prefer native crayfish because they have a softer shell compared to the rusty crayfish and a decrease in the their numbers could limit a food source for fish. The rusty crayfish is also more aggressive and under fish attack will not swim away like the native crayfish, but will hold its claws up in a defensive manner.

The native crayfish species Orconectes virilis and Orconectes propinquus have been displaced in the areas of the Kawartha Lakes region, northern Ontario and the northern Wisconsin lakes by the rusty crayfish (Gunderson, 1995). The rusty crayfish can mate with other species of native crayfish, such as Orconectes propinquus which may hasten the local extinction of the native species.

Prevention

Once introduced, rusty crayfish are difficult to control. Therefore, it is vital to prevent their spread to other waterbodies. Rusty crayfish could accidentally be transported in bait buckets. Crayfish must be used in the same water body where caught. May not be transported overland.  Dump any unused, live crayfish bait in the trash. 

If you think you've caught a rusty crayfish, freeze it or preserve it in alcohol and call the Invading Species Hotline at 1-800-563-7711 or contact your local MNR office.