Amencan Fisheries Society A Regional View of the Margin: Salmonid Abundance and Distribution in the Southern Appalachian Mountains of North Carolina and Virginia

--In the southern Appalachian Mountains, native brook trout Salvelinus fontinalis and introduced rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta are at the southern extremes of their distributions, an often overlooked kind of marginal habitat. At a regional scale composed of the states of Virginia and North Carolina, species were found to be distributed along latitudinal and elevational gradients. Native brook trout remain most common and abundant, decreasing both from north to south and from high to low elevations. Sympatry increases to the south, where rainbow and brown trout become more successful. For the region as a whole and within major drainages, allopatric and sympatric brook trout were generally found at higher elevations and rainbow and brown trout at lower elevations. Among drainages, elevations at which allopatric brook trout and rainbow trout are found generally increased to the south. A measure of effective elevation, which adjusts elevation for latitude, most clearly separated allopatric and sympatric brook trout from allopatric rainbow and brown trout. In the southern Appalachian Mountains, salmonids are at the southern margin of their distributions in eastern North America. The original distribution of brook trout Salvelinus fontinalis, the only native salmonid, extended down the spine of the Appalachian Mountains through western Virginia and North Carolina and eastern Tennesset to northeastern Georgia (MacCrimmon and Campbell 1969). Stockings have not notably extended the distribution of brook trout in the southern Appalachians. Rainbow trout Oncorhynthus mykiss and brown trout Salmo trutta were introduced into the region in the late 19th and early 20th centuries. In this paper I will refer to the three species collectively as “trout.” In the Great Smoky Mountains of North Carolina and Tennessee, introduced rainbow trout have generally been successful at lower elevations, and between the 1930s and the 1970s brook trout have been increasingly restricted to upper headwater reaches (Kelly et al. 1980; Larson and Moore 1985). In Tennessee streams north of Great Smoky Mountains National Park, similar reductions in brook trout distribution during the 1970s have 1 been reported (Bivens et al. 1985). Evidence of similar changes in other areas of the southern Appalachians is anecdotal. Brook trout now occur at the highest elevations, and rainbow and brown trout at lower elevations; up to several kilometers of sympatric coexistence occur between the allopatric sections (Bivens et al. 1985; Larson and Moore 1985). However, studies have been conducted on a limited geographic area in and near the Great Smoky Mountains National Park of North Carolina and Tennessee (e.g., Moore et al. 1983, 1986; Bivenset al. 1985; Larson and Moore 1985) and were not designed to consider patterns over the full range of latitudinal and elevational gradients in the region. Yet, the southern Appalachian region, from northern Virginia to northern Georgia, extends 700 km over 5” of latitude and includes thousands of kilometers of trout stream (Flebbe et al. 1988). Other studies have shown brook trout to be widely distributed and abundant in the Shenandoah National Park of Virginia (500 km north of Great Smoky Mountains National Park), where rainbow trout are rare and of limited distribution (Lennon 196 1). Latitude and elevation are two large-scale geographic factors that can influence trout abundance and distribution patterns, primarily through their influence on stream temperature, which increases with decreasing latitude and elevation. Stream temperature is a basic factor limiting the distribution of poikilothermic species like trout (Brett 1956; Krebs 1972). Temperature regimes governed by latitude and elevation interact with a species’ temperature requirements to form a template of suitable thermal habitats on the regional landscape. Temperature requirements for individual species may be quite complex and depend on season, life stage, acclimation, fish condition, and