Restoration of American Eels to the Susquehanna River Watershed and Implications for Eastern Elliptic Populations

The catadromous American eel occupies a unique niche in estuarine and freshwater habitats along the Atlantic coast. The panmictic population has experienced a range-wide population decline during recent decades.  While the Chesapeake Bay watershed supports a large portion of the coastal eel population, 43% of eel habitat in the watershed is inaccessible due to large mainstem dams in the Susquehanna River.  Future re-licensing of these dams will likely require upstream and downstream eel passage. We have been evaluating upstream migration patterns of juvenile eels below the first dam on the Susquehanna River since 2005. In recent years young eels collected in this survey have been marked with oxytetracycline and stocked into tributaries upstream of the dams to evaluate the effects of reintroduction. Laboratory studies conducted by the USGS, Leetown Science Center indicate that eels are the dominant host for the common freshwater mussel, eastern elliptio (Elliptio complanata) in the Susquehanna River. Relative to the adjacent undammed Delaware River where eels are numerous, abundance and recruitment of eastern elliptio in the Susquehanna River is low. Therefore, we believe low abundance and lack of recruitment of eastern elliptio is related to the lack of eels in the Susquehanna River watershed. We are evaluating the effect of experimental eel stocking on recruitment of eastern elliptio and fish species composition in two tributaries to the Susquehanna River.