A Preliminary Classification System for Large U.S. Reservoirs Based on Fish Habitat

Reservoirs have become numerous, ubiquitous features of the U.S. landscape, providing benefits such as aquatic habitat and recreational opportunities.  Now, reservoirs are aging, and their recreational and ecological values are changing.  If variables acting at multiple spatial scales were synthesized in a single assessment framework, otherwise elusive patterns could emerge in fish habitat and fish community structure.  Understanding these patterns allows reservoirs to be classified and assessed more accurately at the national level.  Classification assists in the identification of common patterns and expectations, as well as in the development of class-specific management strategies.  We conducted a survey of reservoirs ≥ 100 ha in the conterminous U.S.; questions covered numerous habitat attributes – including availability, water quality, water regime, and degradation processes – as well as selected aspects of the fish community, recreational fishery, and the tailwater.  Surveys were completed for ~1,300 reservoirs.  Using the habitat variables, we applied ordination methods to derive orthogonal axes that adequately differentiated reservoirs, and each axis was described using high-loading habitat variables.  Cluster analysis was applied to the reservoirs, and resulting clusters were compared to extant geographic classification systems.  Reservoir classes were chosen that balanced habitat-based clustering with the existing geographically-based framework.