Morphometric and dietary comparisons of co-occurring trout in two adjacent watersheds in the Great Smoky Mountains National Park

Abstract

Food webs are intricate systems produced by evolving networks of community members and trophic interactions. This study investigates dietary shifts of trout in response to changes in foraging competition. Both the Little Cataloochee and Correll Branch watersheds in the Great Smoky Mountains National Park have supported competing populations of brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss). Trout were sampled from both systems before removal of rainbow trout from Little Cataloochee Creek. Geometric morphometric measurements were recorded for 15 landmarks before specimens were dissected to determine sex and extract stomach contents. Prey items were identified to taxonomic order and dietary compositions were compared between species and watersheds. Morphometric differences were tested with Procrustes Analysis of Variance in MorphoJ and dietary differences were tested with Analysis of Similarity conducted in Primer. Significance was set at α=0.05. Brook trout exhibited highly significant morphometric differences among watersheds (p<0.0001) and ontogenetic shifts from juveniles to adults (p=0.0005), whereas rainbow trout did not. Diets were also significantly different between watersheds (p=0.022), but not significantly different between species, gender, or age. The morphometric differences may be due to phenotypic plasticity and genetic diversity of native brook trout compared to the potentially reduced genetic variation of the introduced rainbow trout. Differences among diets between watersheds is most attributed to the presence of terrestrial ants, which may represent a stochastic event that increased their availability in Correll Branch. This study’s findings can be useful for future brook trout conservation and management efforts.