Stable Isotope Analysis (delta nitrogen-15 and delta carbon-13) and Bioenergetic Modeling of Spatial-Temporal Foraging Patterns and Consumption Dynamics in Brown and Rainbow Trout Populations Within Catch-and-Release Areas of Arkansas Tailwaters

I examined spatial and temporal consumption dynamics using an energy intake model and a bioenergetics model of rainbow trout, Oncorhynchus mykiss, and brown trout, Salmo trutta, within three catch-and-release (C-R) areas in Bull Shoals and Norfork tailwaters to determine whether trout populations were limited by food supply. I also examined the seasonal and ontogenetic shifts in the foraging patterns of brown and rainbow trout within these areas using gut content analysis (GCA) and stable isotope analysis (SIA) of C and N. I examined 605 brown trout and 768 rainbow trout for GCA and SIA at Bull Shoals, Norfork, and Sylamore C-R areas. For growth analysis and abundance estimates, I tagged a total of 11,423 brown and rainbow trout. Mean rainbow trout densities were higher (47 to 342 fish*ha-1) than brown trout (3 to 84 fish*ha-1) at all C-R areas. The Norfork C-R area contained the highest densities of brown and rainbow trout. Benthic macroinvertebrates at Bull Shoals and Norfork were 14.0 to 18.7 times higher in biomass than at Sylamore. Biomass of sculpin was approximately 2 to 8 times higher at Norfork than Bull Shoals and Sylamore. I found a high proportion of filamentous algae, Cladophora, and a nuisance diatom, Didymosphenia geminata in the diets of rainbow trout (15-91%), despite the apparent lack of energetic value from this food source. Generally, SIA mixing model results provided broad ranges of source contributions rather than more informative narrow ranges of solutions limiting the conclusions regarding food source contributions. Large rainbow trout failed to consume sufficient food biomass to exceed maintenance ration and exhibited slow or negative seasonal growth suggesting poorer energetic conditions existed for this size class and species. In contrast, brown trout experienced high growth rates at lower densities than rainbow trout. Growth rate differences between brown and rainbow trout may be from brown trout shifting towards the incorporation of more energetically profitable prey fish. These findings suggest rainbow trout, and not brown trout, in Arkansas tailwater C-R areas were limited by spatial-temporal fluctuations in food availability