Invasion of the upper Susquehanna River watershed by rusty crayfish (Orconectes rusticus).
Orconectes rusticus (rusty crayfish) has spread from its original range throughout much of northeastern North America. Invading rusty crayfish can completely replace native crayfish and impact other parts of the community through changes in consumption, disturbance, and other effects. Our main objectives were to document rusty crayfish distribution in streams of the upper Susquehanna River watershed, NY, and to determine the extent of changes in crayfish community composition since the last major survey. We sampled streams during 1999-2005 to describe the current distribution of crayfish species and to document short-term temporal changes. To determine long-term changes in species composition and distribution, we compared our data to museum specimen collection records. We found significant changes in the crayfish community; our surveys found 2 species not previously reported from the upper Susquehanna River watershed and failed to find 2 species previously reported. We also found that rusty crayfish are widespread in the watershed and continues to expand, while the ranges of native congeners are retracting.