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UBC Theses and Dissertations

The influence of geographic scale, climate and trophic dynamics upon North Pacific oceanic ecosystem models Preikshot, David B.

Abstract

Dynamic simulation models of three nested North Pacific ecosystems (the Strait of Georgia, the British Columbia Shelf and the Northeast Pacific) were constructed to examine how area scale affects modelled historic changes of trophic interactions, fisheries and climate. Species groups were the same for all ecosystem models, with a focus upon commercially important fish species. The models were dynamic and spanned the period from 1950 to the start of the 21st Century. Time series data for biological indicators were compared to predicted model time series, under different scenarios of ecosystem control: top-down, bottom-up, or combinations thereof. Results of these scenarios suggest that while fisheries, and predation / competition effects explain most population changes for commercially important fish species, all species modelled also appear to experience bottom-up effects driven by climate change, and regime shifts. The ecosystem models suggest such bottom-up dynamics through predicted primary production anomalies similar to decadal cycling seen in climate indices like the Pacific Decadal Oscillation (Northeast Pacific), upwelling at 54°N (BC shelf) and Salinity / Fraser River discharge (Strait of Georgia). The results of this work suggest that both the area and scale over which indices of regime shifts and climate change are measured are linked, via bottom-up forcing, to changes in biomasses of all trophic levels in these ecosystems. The ability to link bottom-up and top-down dynamics provides an exciting way for ecosystem models to contribute to the formulation of policy and cross validation of single species stock assessment research.

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