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Allegheny Crayfish
(Faxonius obscurus)
Species at a Glance
Also known as the obscure crayfish, the Allegheny Crayfish is a medium-sized crayfish that typically inhabits rocky substrates in streams, rivers, lakes, and reservoirs, and competes for habitat and food resources with native crayfish species. This species has unique management implications, as it is native to the western portion of the state and invasive in eastern drainages, such as the Susquehanna River, where it was likely the first of several non-native crayfish species to invade.
Species Description
The Allegheny Crayfish is found in a range of colors from light brown to olive green, with a dark brown wedge on the dorsal surface of the abdomen. Its rostrum (nose-like structure) is concave and lacks a ridge or keel running down the middle. The chelae (pincers) are large and straight with moderately long fingers and two rows of tubercles along the margin of the palm. While the average size of the carapace is less than 38 mm (1.5 inches) long, the largest individual in Pennsylvania has been documented from Allegheny County with a total length of 93 mm (3.6 in).
Due to its similar coloration, the Northern Clearwater Crayfish may be confused with the Allegheny Crayfish. The key distinguishing feature between these two species is a small bump located on the rostrum of the Northern Clearwater Crayfish. The Allegheny Crayfish can also be mistaken for the invasive Rusty Crayfish, which usually has large red spots on each side of the carapace, where the head and thorax meet, and has smooth mandibles, rather than serrated mandibles found in the Rusty Crayfish. The Allegheny Crayfish can hybridize with either of these species.
Native & Introduced Ranges
The Allegheny Crayfish is native to parts of Maryland, New York, Ohio, Pennsylvania, Virginia, and West Virginia. In Pennsylvania, this species is native to the Lake Erie, Genesee, Allegheny, and Ohio River drainages in the western portions of the state; however recent studies have revealed that it was introduced into the Susquehanna River drainage and portions of the Delaware River drainage and Potomac basin.
Biology & Spread
This species was most likely introduced outside its native range through bait bucket releases. Once introduced, its high reproductive capacity allows it to quickly establish and spread to new areas.
Habitat
The Allegheny Crayfish inhabits large streams, rivers, lakes, and reservoirs with rocky substrates such as sand, gravel, and cobble. It is typically found under large stones or debris in stream beds; however, if larger stones are not present, it may dig shallow tunnels just below the surface along the water’s edge.
Impacts
Threat to Biodiversity
The Allegheny Crayfish threatens native crayfish species by directly competing for food, habitat, and resources, and through hybridization with native species. In parts of the Susquehanna River Basin, the Allegheny Crayfish has nearly eliminated Spiny-cheek Crayfish, along with other native crayfish species.
Prevention & Control
Many chemicals kill crayfish; however, none are currently registered for crayfish control, and none selectively kill the Allegheny Crayfish without killing other crayfish species. The best way to prevent further ecological problems caused by the Allegheny Crayfish is to prevent or slow their spread into new waters.
Never release live bait into any water body and never transport any crayfish from one water body to another. In Pennsylvania it is illegal to possess, import, or transport any crayfish species unless they are used as bait in the water they were taken from, or unless the head is immediately removed above the eyes before transport.
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References:
- Hartzell, S.M. (2020). Life History of an Invasive Population of Allegheny Crayfish (Faxonius obscurus) in Eastern Pennsylvania Stream. Northeastern Naturalist 27:307-317.
- Lieb, D.A., R.W. Bouchard, R.F. Carline, T.R, Nutall, J.R. Wallace, and C. Burkholder. 2011. Conservation and Management of Crayfishes: Lessons from Pennsylvania. Fisheries 36:489-507.
- Ortmann, A.E. 1906. The Crawfishes of the State of Pennsylvania. Memoirs of the Carnegie Museum 2:343-523.
- United States Geological Survey (USGS) Nonindigenous Aquatic Species Database (2019)
- Observation.org (2023)
