Faxonius obscurus

Based on Crandall and De Grave (2017), the representatives of Orconectes form at least two distinct groups. The nominal group (the "cave Orconectes") form a monophyletic group that is more closely related to members of Cambarus, while the remaining "Orconectes" are more closely related to Barbicambarus, Creaserinus, and other species of Cambarus (Crandall and Fitzpatrick 1996, Fetzner 1996). As the type species of Orconectes, Orconectes inermis Cope, 1872, belongs to the cave-dwelling group, the genus is herein restricted to just those taxa. The surface-dwelling taxa now excluded from Orconectes sensu stricto are herein placed in the resurrected genus Faxonius Ortmann, 1905a, the oldest available name previously considered to be a synonym of Orconectes Cope, 1872.

This species is relatively widespread and abundant, but has been eliminated from parts of its range due to the competitive impact of the invasive species O. rusticus, and has shown declines due to acid mine runnoff from strip mining. Whilst these impacts are insufficient to trigger a threatened category listing, these local declines and extirpations should be monitored.

This species ranges from southeastern Ontario and New York to Pennsylvania and eastern Ohio, south to West Virginia, northern Virginia, and western Maryland (Hobbs, 1989). Fitzpatrick (1967) included the Ohio River drainage east of the 81st meridian; Susquehanna, Potomac, and upper Rappahannock River drinages; miscellaneous Lake Erie and Lake Ontario drainages in extreme western New York, northern Pennsylvania, and extreme northeastern Ohio.

This species has been introduced to Massachusetts in the North Branch of the Housic River and some of its tributaries; and in Goose Pond in Lee, Greenwater Pond in Becket, Konkapot Brook in Stockbridge (all Housatonic River system); and in the Housatonic River in Stockbridge (Smith, 2000). Smith (1979) noted that although it occurs in limited areas of the upper Mohawk River system, Fitzpatrick's (1967) deptiction of its presence also in the lower Hudson River and upper Delaware River systems of New York is erroneous. In Maryland, it is distributed from the Piedmont to the Appalachian Plateau but is also in impounements in the Appalachian Plateau and Ridge and Valley Provinces (Kilian et al., 2010) and is known only historically from the Coastal Plain (Meredith and Schwartz, 1960). Jezerinac et al. (1995) considered it native to the Potomic River drainage but Ortmann (1906) suggested it was introduced east of the continental divide in Wills Creek (Potomac tributary near Cumberland, Maryland); thus its native status is unclear in Maryland, however the population in Octoraro Creek (Susquehanna tributary) is most likely an introduction by anglers (Bouchard et al., 2007). In West Virginia, its distribution is primarily allied with the Potomac and ancient Pittsburgh River systems and it occurs throughout the Potomac River drainage, Monongahela River drainage, higher elevations in the Greenbrier River drainage, and central and northern portions of the Ohio River direct drains (Loughman and Welsh, 2010). In Ohio, it is found in tributaries of the Ohio River from Sunfish Creek (Monroe Co.) to Little Beaver Creek (Columbiana Co.) with very little range expansion since the retreat of the Wisconsin Glacier (Thoma and Jezerinac, 2000). Jezerinac (1986) lists Belmont, Columbiana, Jefferson, Mahoning, Monroe, Portage, Stark, and Trumbull Cos., Ohio.

Orconectes obscurus has been displaced by Orconectes rusticus in areas where this invasive crayfish has encroached, as O. rusticus is less vulnerable to predation than O. obscurus (Kuhlmann et al., 2008). O. obscurus has been replaced entirely by O. rusticus in the Sunfish Creek watershed, Ohio (Jezerinac, 1986; R. Thoma, pers. comm., 2009.). This is known to have occurred within a 30 year period. It is also impacted across large areas of its range by acid mine runoff from strip mining which are causing localized population decline. There are still large portions of the range which have not been invaded, and O. obscurus has strong holds in small, forested headwater streams (Thoma and Jezerinac, 2000; Kulmann et al., 2008).