Richard J. Strange and James W. Habera, Department of Forestry, Wildlife and Fisheries, University of Tennessee, Knoxville, TN 38916

Abstract. Lower elevations of brook trout Salvelinus fontinalis distribution in 25 streams in East Tennessee were determined during 1991-1995 to evaluate changes related to encroachment and possible replacement by rainbow trout Oncorhynchus mykiss since surveys conducted from 1978-1984. No efforts to remove rainbow trout or enhance brook trout populations were made in these streams during the 7-16 year intervals between surveys. Compared to earlier distributions, brook trout receded (lower elevation increased) in 9 streams (36%), advanced (lower elevation decreased) in 8 streams (32%) and did not change in 8 streams (32%). The average change in stream length occupied by brook trout was a 109-m increase (SE=82) with a mean annual rate of 8 m (SE=6). Neither average change nor annual rate was significant (P>0.19). Additionally, the uppermost elevation at which rainbow trout were present (determined in 10 streams) increased in 4 streams and decreased in 6. The average change in stream length occupied by rainbow trout was a 158-m decrease (SE=151) with a mean annual rate of -14 m (SE=13). Neither average change nor mean annual rate was significant (P>0.30). We conclude that rainbow trout are not currently affecting the downstream limit of most brook trout populations where the two species occur sympatrically in Tennessee. These data support an emerging theory that the distributional limits of brook and rainbow trout in sympatry in the southern Appalachians ebb and flow upstream and downstream over time.