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Seminar Abstract

John Field - June 3, 2003


Modeling Northeast Pacific Ecosystems

We [John Field, Kerim Aydin, Robert Francis and Sarah Gaichas] have been involved in modeling the major trophic interactions in Northern California Current (NCC) in close collaboration with workers at the Alaska Fisheries Science Center modeling the Gulf of Alaska, the Eastern Bering Sea and the Aleutian Islands. The key objectives are to develop of conceptual models of food webs, estimate how total removals relate to standing biomass, production, optimum yield, natural mortality and trophic structure. In addition to the static snapshots, we have also been exploring dynamic ecosystem simulations; which can be best described as a multi-species biomass-driven predator/prey surplus production model.

Although the modeling framework is limited in its ability to account for some important ecosystem processes, in particular age structure, the simplicity of its assumptions suggest that it is a useful tool for integrating available data and knowledge in a dynamic way. The approach is particularly relevant to evaluating whether observed trends and results from single species assessments are consistent with commonly held notions of ecosystem abundance, productivity, interactions and behavior. A key challenge in doing so has been determining how best to incorporate climate impacts and forcing processes into model dynamics, an effort that requires numerous simplifying assumptions in order to accommodate the modeling framework.

Climate is known to affect the Northern California Current both from the bottom up (through short and long term variability in primary and secondary productivity) as well as from the top-down (through variability in the spatial distribution of key middle and top trophic level predators such as Pacific hake, arrowtooth flounder, albacore, sardine and mackerel). Consequently, it is clear that neither a single index, nor a suite of indices, offers a clear forcing mechanism to explain the dynamics of the system over time. We are hopeful that this approach may be useful in evaluating the role of both fisheries and climate under alternative assumptions of stability, and consequently lead to insights regarding the potential impacts of fisheries at a systems level (albeit that of a simplified system), rather than solely a single species perspective.

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