1. Massachusetts Cooperative Fish and Wildlife Research Unit, Department of Environmental Conservation, University of Massachusetts, Amherst, MA 01003 USA
2. U.S. Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, Department of Environmental Conservation, University of Massachusetts, Amherst, MA 01003 USA
3. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602 USA
4. U.S. Fish and Wildlife Service, Richard Cronin Aquatic Resource Center, Sunderland, MA 01375 USA