NEAFWA 2017

AUTHORS: Scott Stranko, Maryland Department of Natural Resources

ABSTRACT: A great deal of effort is focused on restoring the ecology of streams through changes in the structural aspects of stream channels and improvements to water quality. However, restoring historical biotic interactions is also likely to be important. This includes interactions between migratory fishes and resident biotic communities. The American Eel (Anguilla rostrata) has been excluded from many streams along the Atlantic slope of the USA because of migration barriers such as large dams. Loss of this formerly common top predator has the potential to influence many aspects of headwater streams. We used existing survey data for a landscape-scale comparison of fish, insect, and crayfish densities at 95 sites where American Eel access was excluded by dams and 74 sites containing eels. Benthic fish densities were significantly lower at eel-containing sites, whereas insect densities were significantly higher. Densities of nonbenthic fish, non-eel top predators, and crayfish were not different between eel occurrence categories. While these initial results are correlative, we believe that American Eel may be capable of influencing lower trophic levels, and their presence may produce noticeable changes to headwater stream ecosystems. These findings may have important implications to stream ecological restoration efforts in Maryland and throughout the eastern US.