Closed and Open Marine Fish Populations

For marine fishes, challenges of reproducing in a dispersive environment, advection of young, and transiting through size-structured food webs are met through life cycles that are both closed and open to emigration. Natal homing remains a central premise bolstered by recent discoveries on the remarkable abilities of marine fishes to find their way back home.  Alternate explanations for life cycle closure – imprinting, genetic and cultural transmission, and ecological inheritance – have all received support.  Concepts of open populations, principally applicable over shorter phases of life, consider simple null models of dispersion and more elaborate density-dependent models.  Reef-associated fishes have attracted substantial interest in the open nature of populations.  Larval connectivity studies in these and other populations track the oceanographic fates of larvae depending on their origin. The dual open and closed nature of populations of marine fishes is well accommodated by metapopulation models, which explicitly recognize the role of straying in persistence.  On the other hand, this dual state confounds central simplifying assumptions in fisheries stock assessment that attempts to define populations as unit stocks.  Examples of misspecified stock structure are highlighted as well as advances in stock assessment approaches that incorporate more complex population structure into management advice.