Vitenskapelig sammendrag
We propose to study the physical and biological mechanisms that generate and maintain a highly geneticallystructured population of cod in the Skagerrak water system. We hypothesize that acombination of oceanographic features (i.e., within fjords water circulation), spawning behavior (i.e. strongphylopatry), and ecological traits (i.e. lower mortality of locally retained early-life stages) contribute to maintain theobserved genetic differentiation of the returning adults. It is thus proposed to (1) study the inflow of North-Sealarvae to Norwegian Skagerrak fjords with focus on linking physics with population structure and dynamics, and (2) to study the maintenance of costal cod populations within fjords focusing on linking physics, behavior and biology.Issue (1) involves improving models of the linkages between North Sea spawning cod and local fjord populations ofcod in the Skagerrak,explicitly considering the sub-structuring of the North Sea cod population and the variability of the oceanicdynamics. Issue (2) involves a detailed field study of spawning site selection, egg retention, larval drift, and currentpatterns in two representative fjords, to understand the mechanisms for maintaining local populations. Furthermoreissue (2) requires developing and analyzing evolutionary and physical models to assess the degree to whichmature coastal cod spawn at optimal sites so as tomaximize the probability of the spawning products staying within the fjord given the dynamics of the local watermasses. Our proposed work, besides being highly relevant to manage an economically important Norwegianresource, also has broader ecological relevance, in that it addresses an issue at the core of evolutionary biology:the generation and maintenance of genetic structure in marine fish populations
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