It Doesn't Get Any Better Than This: The Distribution, Biomass, and Abundance of American Eel in Headwaters of the Undammed Delaware River

The American eel (Anguilla rostrata) stock has declined across its range over the past four decades due to dams, overfishing, and other stressors. The Nature Conservancy and US Geological Survey quantified fish assemblages in tributaries of the Delaware River (in NY, NJ, and PA) during 2002-08 to evaluate the present-day status and potential effects of impoundments on eel distribution and fish communities. American eel were extirpated from sites upstream of large dams, whereas, eel density ranged from 0.001-0.130 eel m^-2 and biomass ranged from 0.01-11.82 g m^-2 at downstream sites. Density and biomass of eels were often comparable to, or greater than that of salmonids at sites that included small high elevation trout streams. The loss of eels at sites located upstream of major impoundments provides insight into the direct and indirect effects of dams on this important species as well as the entire fish assemblage in regulated rivers. The distribution, abundance, and biomass of American eel in some undammed headwater reaches of tributaries to the Delaware may represent near-reference conditions for the species across its range and this type of information could be used to inform the effectiveness of eel-management and restoration efforts in other areas.