The Effects Of Beaver Impoundments On Montane Stream Fish Communities

North American beavers (Castor canadensis) are ecological engineers, and their dams alter stream environments. Few studies have examined the effect of beaver dams on Southern Appalachian fishes. I sampled fish communities from 9 streams with active beaver ponds and 7 with inactive beaver ponds. Sediment was taken from all ponds to quantify the abundance of oligochaete worms, potential hosts for the fish parasite Myxobolus cerebralis. I found that both active and inactive beaver impoundments affect water quality, fish communities, and oligochaete prevalence. Generalized linear mixed effect models (GLMMs) indicate reduced fish diversity in streams with active impoundments. The magnitude of this reduction depends on the proximity to an impoundment. Models indicate that site elevation plays the strongest role in determining fish species richness. Active ponds also had lower dissolved oxygen and temperatures. Indicator species analysis found two species associated with active beaver ponds and 8 associated with inactive ponds or unimpounded reaches. Oligochaetes were more prevalent in active ponds, but I detected no abnormal salmonids. My work indicates that Appalachian Mountain streams with active ponds support less diverse fish assemblages than those with inactive ponds. Beaver ponds improve habitat for oligochaetes but their role in fish disease transmission remains unclear.