Diet Niche Width and Individual Specialization of Brook Trout in Adirondack Lakes

We evaluated diet niche width, individual diet specialization, and diet composition in six lake populations of Brook Trout Salvelinus fontinalis, a generalist predator known to exhibit benthic and pelagic trophic specialization. Population diet niche width was broad and similar across all lakes, contrasting with that of individual fish, which exhibited specialized diets in comparison with their population and other individuals. Overall, the degree of individual diet specialization was high compared with that of other fishes. The degree of individual diet specialization did not differ among study populations, although it was generally reduced in spring. Individual diet specialization was consistent across fish sizes despite observed shifts in diet composition with increasing fish length. Population diet composition varied among lakes but was consistent within lakes in all years during the 3-year study period with regard to season and fish size. The consistency and stability in measures of population diet niche width, degree of individual diet specialization, and population diet composition for Brook Trout indicate that these metrics provide useful tools for characterizing fish foraging and measuring how it changes in response to biotic and abiotic perturbations.