A Crayfish Survey of the Fishing Creek Watershed in Northeastern Pennsylvania

Introductions of invasive crayfish species have impacted freshwater ecosystems worldwide, typically resulting in displacement of native crayfish species by non-native species. Two crayfish species (Orconectes limosus and Cambarus bartonii) are thought to be native to the Susquehanna River Drainage in eastern and central Pennsylvania. However, several non-native crayfish (e.g., O. obscurus, O. rusticus, O. virilus) have been introduced and have become established in this river system. Few data are available on the present occurrence and distribution of crayfish species within the Fishing Creek watershed, a drainage encompassing approximately 620 km2 within the North Branch Susquehanna River Drainage in eastern Pennsylvania. Records from the early 1900s report the occurrence of both O. limosus and C. bartonii in this watershed; however, recent point-surveys in the lower reaches of the watershed have reported the presence of the non-native crayfish Orconectes obscurus. In this work, crayfish were sampled at fifteen sites from the lower reaches of Fishing Creek to its headwater branches and major tributaries in order to elucidate the current presence and distribution of crayfish species within this watershed. A total of 484 crayfish were collected, representing the species O. obscurus (n = 376) and C. bartonii (n = 108). O. obscurus were found to be widespread within the drainage, but absent from the upper reaches of the Fishing Creek watershed, potentially as a result of physical or environmental barriers (e.g., dams, shifting stream characteristics). C. bartonii were primarily distributed in the upper portions of the Fishing Creek watershed, but also found in smaller tributary near the mouth, and sympatric (but in found in low abundance) with O. obscurus in the central portions of the drainage. This distribution of C. bartonii within the watershed is likely due to habitat preferences (e.g., cooler, smaller, and higher gradient portions of streams) of this species, but may also result from displacement by O. obscurus. The historically present O. limosus was not collected within the watershed, potentially suggesting local extirpation via competition with O. obscurus, as has been reported in other elsewhere in aquatic ecosystems invaded by non-native congeners