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Range DescriptionIn the United States, NatureServe (2009) have classified this species as Critically Imperilled in Connecticut, Maryland, Massachusetts, North Carolina, New Hampshire, New Jersey, New York, Pennsylvania, Virginia, Vermont; and Possibly Extirpated in District of Columbia and Delaware. The U.S Fish and Wildlife Service found this species to be declining in Virginia and North Carolina. They found small populations remaining in Maryland, while large populations were found in New Hampshire, and additional populations were discovered in the Delaware River watershed in Pennsylvania, New Jersey and New York (USFWS 2007). Since the publication of the U.S. Fish and Wildlife Service report, new populations have been reported in North Carolina (A. Bogan pers. comm. 2010).
In Canada, this species is extirpated in New Brunswick. This population was geographically isolated from U.S. populations (possibly for as long as 50,000 years) and may have developed unique genetic characteristics (Canada Department of Fisheries and Oceans 2007).
Because of its severely fragmented distribution, the area of occupancy for this species is estimated as between 500 and 2,000 km².