Effects of Dams, Reservoirs, and Tailwaters on Functional Connectivity in the Upper Tennessee River Basin

Humans have altered the structural connectivity of rivers to an extent unrivaled in any other landscape type.  A dramatic example is the upper Tennessee River basin (UTRB), which is bisected by 24 hydroelectric dams.  While dams themselves likely are strong barriers to movement of riverine species, associated reservoirs and tailwaters may also impede connectivity.  Such hypotheses are largely untested, because functional connectivity is difficult to assess using traditional techniques.  We measured the functional connectivity of the UTRB for redline and greenside darters using microsatellite genetic markers. These species were selected to represent the diverse darter fauna of the UTRB, and because they are important host species for larval freshwater mussels, which rely upon fish for dispersal.  Collective results of this study plus other studies we reviewed demonstrate pervasive decreases in connectivity among riverine fish populations separated by dams, reservoirs, and tailwaters.  This lost connectivity also drives fragmentation of mussel populations, but reduction of mussel gene flow will take longer to observe because of the long generation times of most species. Because fragmentation reduces both dispersal and population size, it has profound implications for the persistence and co-evolution of the UTRB’s globally significant fish and mussel fauna.