No abstract

Lowest distributional elevations for brook trout Salvelinus fontinalis 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 during [1978][1979][1980][1981][1982][1983][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 with the earlier surveys, brook trout distributions receded (lower elevation increased) in nine streams (36%), advanced (lower elevation decreased) in eight streams (32%), and did not change in eight streams (32%). The average total change in stream length occupied by brook trout was a 109-m downstream increase (SE ϭ 82) with a mean annual increase of 8 m (SE ϭ 6). Neither average total change nor annual change was significant (P Ͼ 0.19). Additionally, the highest elevations at which rainbow trout were present (determined in 10 streams) increased in four streams but decreased in six. The average total change in stream length occupied by rainbow trout was a 158-m decrease in elevation (SE ϭ 151) with a mean annual change of Ϫ14 m (SE ϭ 13). Neither average total change nor mean annual change was significant (P Ͼ 0.30). We concluded that rainbow trout were not affecting the downstream limit of most brook trout populations where the two species occurred sympatrically in Tennessee. Further, after examining published data from Great Smoky Mountains National Park, we found no evidence that the downstream limits of brook trout distribution in most streams were affected by the presence of rainbow trout between the 1950s and 1970s. These data support an emerging theory that the distributional limits of brook trout and rainbow trout in sympatry in the southern Appalachian Mountains will ebb and flow upstream and downstream over time.

We evaluated three-pass depletion sampling for both AC and pulsed-DC electrofishing for estimating the population size of rainbow trout Oncorhynchus mykiss in a representative low-conductivity (20-lS/cm) southern Appalachian stream with limited habitat complexity. Trout capture efficiencies in such streams could be expected to exceed those observed in streams in which habitat is more complex; thus, depletion estimates could be much more accurate in the former. We also compared the results for two trout length-groups to investigate size-related differences. Measured capture efficiency was 0.88 6 0.04 (95% confidence interval) for trout greater than 100 mm (typically adults) and 0.65 6 0.09 for trout less than 100 mm (age 0). Population size was underestimated in each depletion sample. The errors for trout over 100 mm were generally small (mean, 12%; range, 3-23%), and the upper 95% confidence limits were usually within 10% of the true population size (N). Underestimates of N were larger for trout under 100 mm (mean, 32%; range, 5-60%), although the upper 95% confidence limits were within 20% of the N for half of the samples. The results of a laboratory study confirmed that trout over 100 mm were immobilized at significantly lower voltage gradients than were smaller trout in both electric fields. We conclude that three-pass depletion sampling is relatively accurate in typical southern Appalachian trout streams and that the underestimation errors for rainbow trout larger than 100 mm would be acceptable given basic inventory and monitoring goals.

Previous research has indicated that native southern Appalachian brook trout Salvelinus fotinalis are genetically distinct from hatchery stocks derived from northeastern populations. Six diagnostic allozyme loci identified in earlier research were used to assess the genetic origin of 38 Tennessee brook trout populations outside of Great Smoky Mountains National Park. Twenty‐two of these populations (58%) were putatively native, eight (21%) were derived from hatchery stocks, and eight (21 %) were hybrids. Significant genetic differences among the 22 native populations were observed, and genetic structure among these populations was high (genetic variance index FST = 0.622). Thirty‐two percent of the genetic variation among native populations was attributable to differences within watersheds, whereas 29% was attributable to variation among the five major watersheds containing brook trout. Populations located north (19) and south (3) of the French Broad River clustered separately, based on a genetic distance index. Knowledge of the genetic characteristics of brook trout populations will enable fisheries managers to make more informed decisions about this resource in Tennessee and elsewhere in the southern Appalachians. Given that maintaining the genetic integrity of native southern Appalachian brook trout is an important goal, our findings will help managers to design strategies that require stocking or stock transfers to create or expand populations.

Information acquired through surveys of six state and federal natural resource management agencies was used to obtain current estimates of the wild trout resources of the southern Appalachian Mountains and to review associated management programs. Overall, the southern Appalachians contain some 18,000 km of coldwater streams with the potential for supporting salmonid populations. Wild trout inhabit about 9,660 km of these streams and native brook trout are found in approximately 2,580 km. These substantial and comparatively unique resources are becoming increasingly important from many perspectives as potential threats to their continued existence increase. Current management programs and strategies employed by the agencies surveyed reflect the basic similarity of wild trout resources and management needs throughout the region. A notable amount of variability remains regarding angling regulations and, to a lesser degree, native brook trout management. Such variability is not biologically‐based, but rather reflects public influences in wild trout management schemes. Generally, the efficacy of wild trout management has improved as greater knowledge and understanding of the region's wild trout resources is obtained and management programs and strategies are further refined. The southern Appalachians provide an example of a collective transition toward more progressive management of a valuable fishery resource.