Consequences of Connectivity Patterns for Stock Assessment and Fishery Management

The degree and patterns of connectivity among population components of marine fishery resources need to be identified to meet fishery management objectives because they influence productivity.  Technological advancements in molecular genetics, electronic tagging, image analysis, and otolith chemistry/microstructure have recently revealed complex patterns of population connectivity and heterogeneity.  Recent genetic analyses showed sympatric patterns of reproductive isolation than the simpler allopatric patterns that were typically assumed for spatial management units.  The observed mechanisms of reproductive isolation include spawning site fidelity (Atlantic cod, Gadus morhua), discrete or semi-discrete spawning grounds (Atlantic salmon Salmo salar; Atlantic bluefin tuna Thunnus thynnus; and winter flounder, Pseudopleuronectes americanus) and divergent adaptation to different adult habitats (beaked redfish, Sebastes mentella).  For other species, even low frequencies of mixing among spawning groups homogenize genetic composition, but high frequency of residence in different environments produce distinct allopatric differences in phenotypic traits such as morphology, growth and reproductive rates that are important for population dynamics (e.g., yellowtail flounder, Limanda ferruginea; American lobster Homarus americanus; Atlantic herring, Clupea harengus; and scup Stenotomus chrysops).  A third group of species appear to have more homogeneous populations that exhibit extensive migrations among feeding, spawning and fishing grounds (e.g., walleye pollock, Theragra chalcogramma).  Spatially-explicit population modeling demonstrates that productivity is profoundly influenced by these various forms of connectivity, and processes that are important for fishery management (e.g., rebuilding, overfishing) as well as the achievement of management objectives such as optimum yield.