Nonlinearity, Irreversibility and Surprise: Managing Atlantic Cod under Climate Change

Anna's dissertation asks what drives the collapse and what drives the recovery of a fish stock in a changing environment. Using Atlantic cod, one of the North Atlantic's most prominent species, as its example, the dissertation examines how rising ocean temperature, temperature variability, ocean acidification and uncertainty affect stock productivity, both individually and in combination. Anna pays particular attention to nonlinear dynamics, including Allee effects, in which per capita growth declines at small population sizes; such effects can hinder recovery, reinforce degradation and make a collapse effectively irreversible. The dissertation then contrasts Canada's fisheries policy and advisory process with the European Union's Common Fisheries Policy, focusing on the precautionary approach and the role of science, to identify the policy and institutional constraints that have hindered sustainable management. Drawing these strands together, Anna concludes with suggestions for scientifically informed, precautionary fisheries management that can speed up stock recovery and support a viable fishery in the future. The dissertation was defended at the University of Oslo in 2021.