Fish and Benthic Macroinvertebrate Densities in Small Streams with and without American Eels

Abstract

The American Eel Anguilla rostrata has been excluded from many streams along the Atlantic slope of the USA because of movement 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, benthic macroinvertebrate, 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 benthic macroinvertebrate 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.

Received July 31, 2013; accepted January 20, 2014

ACKNOWLEDGMENTS

We thank W. Harbold, J. Zimmerman, M. Kashiwagi, A. Becker, P. Graves, K. Hanna, R. Bourquin, and L. Roberson for assistance with data collection and management; S. Gresens, P. Ciccotto, R. Klauda, and D. Boward for guidance and editing; and three anonymous reviewers. American Rivers and the National Oceanic and Atmospheric Administration provided funding for partial financial support and the impetus for the study. We also extend our gratitude to the long list of diligent, hard-working MBSS field sampling crew members, seasonal employees, interns, and volunteers who collected much of the Maryland Department of Natural Resources data presented in this study.