Climate and fishing impacts on North Pacific fisheries: Insights and projections from contrasting approaches to ecosystem modeling
Climate change and fishing are among the greatest anthropogenic stressors on marine ecosystems. Ecosystem models are one tool for evaluating the effects of these stressors, and ecosystem model comparison is a particularly effective method for identifying robust projections of future ecosystem change. When fundamentally different approaches produce the same result, this increases confidence in the conclusion. Conversely, areas of model disagreement highlight topics for future research. This dissertation uses output from a suite of earth system models to determine the range of climate change effects projected for the North Pacific over the 21st century. It then pairs this output with three types of ecosystem models: a size-based, a species-based, and an integrated size- and species-based model. There is broad model agreement that climate change will lead to reduced fish biomass and fishery yield over the 21st century and that increasing fishing mortality will amplify this decline. Furthermore, Hawaii’s longline fishery may move northeastward away from Hawaii in response to these changes. Examining the structure of the ecosystem models used provides insight into the mechanisms driving ecosystem change. Reduced plankton biomass is projected to reduce food availability to fish, reducing their growth and in turn, biomass. Additionally, a shift toward smaller plankton is expected to propagate through the food web leading to smaller fish body sizes. Comparison across ecosystem models also highlights areas for future research. These areas include evaluating the role that food limitation plays in fishes’ foraging behavior and compiling basic life history information for species with high bycatch rates. The results of this dissertation highlight the urgent need to limit anthropogenic climate change and to account for climate change in fisheries management. We cannot hope to catch ever more fish while at the same time we erode the ecosystem’s productivity and capacity.