Condition, Diet, and Trophic Relations of Stocked Trout in Appalachian Streams

We evaluated changes in fish condition and diet composition, and conducted a stable isotope analysis (SIA) of western North Carolina streams that were supported by stockings of Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss.  Recaptures of harvested fish indicated overall declines in fish weight with large individuals losing proportionally more.  Mean relative weight of all species declined from 102 (SE = 1.1) to 87 (SE = 0.8) in the North Toe River (N = 112) and from 104 (SE = 1.8) to 94 (SE = 1.8) in the East Prong Roaring River (N = 58).  Overall, 40% of 141 hatchery-reared trout stomachs collected from both streams were empty; whereas only 15% of 26 wild trout stomachs were empty.  Differences in mean sulfur isotope ratios (P < 0.0001) between wild and hatchery-reared trout indicated that diets of wild fish were enriched in ³⁴S relative to those of hatchery-reared fish.  Although hatchery-reared trout appear to be consuming similar food items to wild fish, differences in diet contribution or reduced feeding may have resulted in lower condition and negative growth.  These findings may enhance management and economic efficiency in refining fish stocking timing, densities, and spatial distribution.