Effects of Space and Scale in the Food Web Structure of the Aleutian Archipelago

One of the challenges in fisheries management as it moves from a single-species to an ecosystem approach, is to meet the ecological and management needs of fish, seabirds, marine mammals, and humans, all of which operate over widely different spatial scales. This relatively new approach to fisheries management involves developing and fine-tuning predictive models that incorporate complex food web structures with the goal of ecosystem sustainability. A food web is a system of predator/prey relationships by which energy is passed through the parts of the system. The study of changes in the structure or function of food webs over time and space helps in our understanding of critical relationships within an ecosystem. Building successful ecosystem models requires understanding changes in the food web structure of an ecosystem depending on location. Large-scale food web models in fisheries management can adequately portray differences across ecosystems and their main features. However, largescale food web models may not accurately represent local areas within ecosystems or those areas that comprise smaller portions of the ecosystem. With support from the Alaska Fisheries Science Center’s Resource Ecology and Ecosystems Modeling Program, we conducted a study of the effects of space and scale in the food web structure of the Aleutian Archipelago, one of the most productive fishing grounds in the nation. Our study used two ecosystem modeling approaches: 1) a largescale food web model based on the Aleutian Islands management region, which geographically includes the central and western (U.S.) Aleutian Islands only; and 2) a series of 13 simplified standardized contiguous food web models for each 2-longitudinal degree block covering the U.S. portion of the entire eastern, central, and western Aleutian Islands. The current management structure of the Aleutian Archipelago, as defined by the North Pacific Fishery Management Council (NPFMC), includes three regions: the Aleutian Islands (AI), Bering Sea (BS), and Gulf of Alaska (GOA). Using the large-scale food web model, we identified energy flow, predator-prey relationships, and fisheries for the Aleutian Islands management region. We then compared this model to those large-scale models for the BS and GOA and identified differences between them in basal energy pools, feeding habits, and fisheries and predation mortality. Next, using the contiguous simplified food web models