Rusty Crayfish
Rusty crayfish are an invasive species that cause damage to Colorado's ecosystem.
About This Species
Rusty Crayfish are not native to Colorado. They are a larger, more aggressive freshwater crayfish than our native crayfish.
Rusty Crayfish in Colorado
Rusty crayfish are believed to have been introduced to Colorado by anglers as bait and throw unused bait into the water or illegally stocked as a prey base for a fishery. Crayfish were also harvested for regional bait markets and for biological supply companies, activities which probably helped spread the species further.
Environmentally safe ways to eradicate or control populations of rusty crayfish have not been developed. Some chemicals selectively kill crayfish, but none are currently registered for crayfish control or are able to remove rusty crayfish without also killing native crayfish species. Intensive harvest may help reduce adult populations and minimize some impacts. The harvest of rusty crayfish for food may provide the only beneficial use for this exotic. The best way to prevent further ecological problems is to prevent or slow their spread into new waters.
Use only Colorado bait: never bring in live aquatic bait from another state.
Crayfish can be taken for personal consumption in Colorado, but care should be taken with their use and disposal. Even though crayfish can be taken live east of the Continental Divide, it is recommended that tails of all crayfish be removed immediately and packed in ice for transport.
Do not throw unused bait crayfish, or bait of any kind, back in the water alive.
Do not dispose of pets or unwanted aquarium plants or animals in natural systems. Never dump or release plants or animals in reservoirs, lakes, ponds, rivers, streams or any water body.
Infected Colorado Waters
Colorado Parks and Wildlife is monitoring the state’s waters for the introduction of an aggressive invasive species, the rusty crayfish. Populations have been managed through manual removal of adult rusty crayfish to reduce the reproducing population in the reservoirs and limit impacts to native communities and users.
Waters Postive for Rusty Crayfish
Rusty crayfish were first detected in Colorado in the Yampa River and Catamount Reservoir in 2009, then again in Sanchez State Wildlife Area in 2010 and in Stagecoach Reservoir State Park in 2011. Populations have been managed through manual removal of adult rusty crayfish to reduce the reproducing population in the reservoirs and limit impacts to native communities and users.
Find out moreReport a Sighting
If you have caught or seen a rusty crayfish, please dispatch it immediately and let us know!
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Physical Characteristics
Size
Rusty crayfish grow up to five inches long. Males tend to be larger than females.
Color
They have brown bodies and large grayish-green to reddish-brown claws with dark black bands on the tips. There are two rusty patches on either side of the crayfish’s body near the area where one would place a thumb and finger to pick the animal up.
Claws
The claws, when closed, have an oval gap in the middle. The moveable claw is smooth and S-shaped.
Commonly Found
Rusty crayfish are native to the Ohio River Basin. They were first discovered outside of their native range in the 1960’s.
Habitat
Rusty crayfish inhabit lakes, ponds, and both pool and fast-water areas of streams, which makes many areas in Colorado potentially suitable habitat.
Diet
They are considered opportunistic feeders and will eat a variety of aquatic plants, benthic invertebrates (like aquatic worms, snails, leeches, clams, aquatic insects, side-swimmers and waterfleas), detritus (decaying plants and animals including bacteria and fungi), fish eggs, and small fish. These crayfish will eat small fish, aquatic insects, eggs and even aquatic vegetation, damaging underwater habitat that is important for fish spawning, cover and food.
Reproduction
Crayfish reproduce by sexual reproduction, but both a male and a female crayfish are not necessary to begin a new infestation. One female carrying viable sperm could begin a new population if released into a suitable environment.
Threats to Species
Native crayfish are susceptible to bacteria and viruses which could be introduced by the rusty crayfish. Rusty Crayfish may harm fish populations by eating fish eggs, but there are no studies linking fishery declines with egg predation. Juvenile rusty crayfish feed heavily on benthic invertebrates, which causes competition with juvenile fish. Although fish will eat rusty crayfish, their food quality is not as high as many of the invertebrates they replace. Their aggressiveness and high metabolic rates allow them to destroy aquatic plants, causing decreased plant abundance and diversity. This causes decreases in habitat for invertebrates, shelter for young fish, forage for some species of fish, fish nesting substrates and increases erosion. They are an aggressive species that displace native crayfish through crayfish-to-crayfish competition, forcing other crayfish species from daytime hiding places which renders them vulnerable to predation by fish.