Spatial analysis of American Eel (Anguilla rostrata), fish passage and land use in Chesapeake Bay tributaries

Catadromous eels are found in more habitats than any other fish and are capable of inhabiting marine, brackish and freshwater environments. In this study we used the American Eel (Anguilla rostrata) as a bioindicator organism to create a novel method of using spatial analysis to study species conservation over landscape scales. We built a model of the subwatersheds of the Chesapeake Bay using a Digital Elevation Model (DEM) and overlaid eel density data (> 1 million eels sampled), dam density data and land use in ArcGIS. Dam construction in the study area peaked between 1955 and 1975, possibly as a result of flood control measures. Effects of land use were localized and most pronounced in areas around Baltimore, Maryland, Washington, D.C. and Richmond, Virginia, USA. Results indicate the Potomac and Rappahannock rivers appear to be areas of lesser concern while the upper James and York rivers are ideal for follow-up studies, since these area rank poorly in both eel density and barriers to fish passage. Because these rivers have high eel density downstream, the dams appear to be the limiting factor. Sampling methods have been inconsistent over time, making it is difficult to determine where eel densities are low vs. the area having had little sampling effort. This is partially resolved with catch per sampling event (CPSE), which appears to show a relationship between eels sampled and the number caught per sample. Potential strategies for improving watersheds include dam removal, fish passage and habitat restoration.