Ecological and fisheries consequences of a mismatch between biological population structure and mangament units of Atlantic cod in US waters

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A mismatch between biological population structure of a species and spatial management units of the fishery can present problems, because the scale of management action should match the scale of biological processes. We hypothesized that recognition of fine-scale population structuring of Atlantic cod in US waters will redefine our perceptions of the productivity, stability, and sustainable yield of the regional population. The goal of our study was to use simulation modelling as a tool to examine the ecological and fisheries consequences of a mismatch between management unit and biological population structure, as defined by genetic analysis, of Atlantic cod. Two agestructured simulation models were compared to test our hypothesis: (i) the management unit model, wherein fish were grouped based on the current spatially defined US management areas (Gulf of Maine and Georges Bank), and (ii) the biological structure model, which consisted of three genetically defined population components (northern spring-spawning, southern winter/springspawning, and Georges Bank spring-spawning groups), with some mixing of early life stages. Productivity and yield of the biological structure model was lower than that of the management unit model because of consideration of the unique vital rates and dynamics of, and connectivity between, spawning groups. Stability of the system, however, was enhanced through these same attributes. Consideration of biological structure of cod changed our perception of the magnitude and distribution of productivity in the region, suggesting that expectations of productivity of Georges Bank cod should be reconsidered.