Historical Changes in Large River Fish Assemblages of the Americas
The Susquehanna River Fish Assemblage: Surveys, Composition, and Changes
Blaine D. Snyder
Abstract.—The Susquehanna River drains portions of New York, Pennsylvania, and Maryland, and is the 18th largest river (by discharge) in the United States. Although relatively undeveloped (i.e., 63% of the basin is forested, whereas 9% is urban), the river and its fish assemblage have experienced stresses associated with coal mining, logging, electric power generation, population growth, and agricultural and industrial operations. Surveys of Susquehanna River fishes have a rich history, with the qualitative surveys of 19th century naturalists giving way to the quantitative studies of 20th century environmental impact assessment specialists. Ichthyofaunal surveys of the Susquehanna drainage were compiled and summarized herein to examine species composition, losses, and additions. Collection records indicate that the Susquehanna River drainage supports a diverse and relatively stable assemblage of 60 native species (or 51% of all species), 33 (28%) alien species, 22 (19%) euryhaline or diadromous fishes, and 2 (2%) extirpated or extinct species. Stocking efforts, bait-bucket releases, range extensions, and new species descriptions accounted for most contemporary species additions. Overall reduction in species richness has been limited to one cyprinid that has not been collected since 1862, and one darter species that has not been collected since 1987. Construction of four large hydroelectric dams on the lower Susquehanna (in the early 20th century) eliminated 98% of historic anadromous fish habitat, leading to notable reductions in commercial/ recreational clupeid stocks. Recent increases in the occurrence and abundance of anadromous fish in the Susquehanna River are a credit to an extensive restoration program that began with fish trap and transfer operations in 1972, included fish culture programs, and led to the installation of fish passage technologies at each of the four dams.
Whereas an abundance of general survey and species account information is available for the Susquehanna drainage, assessments of temporal change in fish assemblage composition and abundance have been limited. The extensive quantitative fish monitoring data collected at three nuclear power stations during the 1970s and 1980s offer benchmarks for trend studies of Susquehanna fishes. The greatest challenge will be generating interest and funding to support such trend assessments of Susquehanna River fish resources.