Crayfish of the Susquehanna River

Concern has been raised over the past decade regarding the conservation status of many crayfish species globally.  Crayfish conservation efforts have been complicated by the spread of nonindigenous crayfish that often competitively exclude native species.  To better understand the status of crayfish in the Susquehanna Drainage, I sampled them at 11 locations along a 400-km reach of the Susquehanna River.  Sampling was done with baited-wire traps specifically designed for river environments.  I placed100 traps at each location for 48 hours from June through August 2008 (2200 trap nights total).  This resulted in the capture of 804 crayfish of two species, the native Allegheny crayfish (Orconectes obscurus), and the invasive rusty crayfish (O. rusticus).  Rusty crayfish were collected at five of the sampling sites; two upriver sites and three downriver sites.  The sex ratios of captured specimens at the combined sites were approximately equal (1.00 and 1.05 for O. rusticus and O. obscurus, respectively).  In general, more specimens of O. rusticus were collected than O. obscurus, indicating greater relative abundances and perhaps densities of this invasive species.  The divided distribution of O. rusticus along this reach of the Susquehanna River suggests that their introduction occurred via bait buckets.