A model of the trophic dynamics among key macroinvertebrate and fish populations in the New River, West Virginia, was developed to help define the roles of predation, competition, and fishery exploitation in the food web of this large, warmwater stream. The fates of production of the harvested crayfish (Orconectes virilis, Orconectes sanbornii sanbornii, and Cambarus sciotensis), hellgrammite (Corydalus cornutus larvae), smallmouth bass (Micropterus dolomieui), rock bass (Ambloplites rupestris), and flathead catfish (Pylodictis olivaris) populations were quantified to evaluate the status of these stocks and to aid specification of the model. Analysis and application of the model were designed to address three research objectives, which were to (1) quantify the roles that predation, competition, and exploitation have in structuring the prey-predator assemblage, (2) evaluate through simulation the effects of multispecies exploitation, and (3) assess through simulation the impacts to the food web of reductions in aquatic insect production associated with the systematic control of black fly larvae in the New River.

The trophic basis of production of smallmouth bass, rock bass, and flathead catfish was primarily aquatic insects (in young fishes) and crayfish (in older fishes). Hellgrammites and prey fishes were inconsequential in that regard. Predation by these fishes (primarily smallmouth bass and rock bass) accounted for 76% of the production of ages-1 and -2 crayfish, and harvest by people was equivalent to 5% of crayfish production. Fish predation (primarily by rock bass) and harvest accounted for 14% and 8%, respectively, of the annual production of ages-1 and -2 hellgrammites. Anglers harvested the equivalents of about 91% and 12% of the annual production of fully-recruited smallmouth bass and rock bass, respectively; the extent of flathead catfish harvest was unclear.

Error analysis of the model suggested that “bottom-up" (food-limitation) effects were more important than “top-down" (mortality from predation) effects, interspecific and intraspecific competition, and exploitation in maintaining the structure of the prey-predator assemblage in the New River. Exploitation was important in causing transitions in assemblage structure. Simulations of multispecies exploitation demonstrated that production and yield of populations are strongly dependent on food web interactions. Simulation of a 50% reduction in aquatic insect production, similar to that observed following poisoning of black fly Iarvae, predicted substantial declines in insectivores and their predators. Management of New River resources for maxi- mum benefits to people will necessarily involve new approaches to addressing problems in a food web context.