Range Description

Pacifastacus nigrescens was originally described from the vicinity of San Francisco, and reported from the hills on the north side of San Francisco Bay. This species was once common in the creeks surrounding the San Francisco bay; however, it has not been observed since the Signal Crayfish (Pacifastacus leniusculus) was introduced to California (probably 1800s- Bouchard 1977) and is believed to be Extinct (Rogers 2005). There have been no authenticated collections in 20th Century. Specific searches by Riegel (1959) and Bouchard (1977) found no extant populations. In 1980 and 1981 searches by McGriff also found no extant populations. All localities had populations of either Pacifastacus leniusculus or Procambarus clarkii (both implicated in the extinction of this species) and the habitat was greatly modified especially by urban development in the last hundred years (J. Cordeiro pers. comm. 2010).