The depletion of a great many conventional fish stocks is urgent testimony for fisheries management to evaluate risk and uncertainty in an interpretable manner. We propose a novel decision based approach to time-series analysis that explores the spectrum of alternative population trajectories, each of which can be formulated as hypotheses about the state of the fishery. In the first chapter, we evaluate the ability of different regions of the surplus production state space to describe the true state of three North American fisheries: Pacific cod, porbeagle shark and yellowtail flounder. We consider how environmental variability and life history traits may alter our assumptions about population productivity, and we lay the foundation for a decision based age-structured analysis. In the second chapter, the approach is extended further into the ecological realm by considering how community interactions between Atlantic cod and harp seals can be represented in state space. Our results indicate that since the fishing moratorium in 1992, harp seals have potentially lowered cod productivity, preventing their recovery.

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