Dynamics and genetics of oceanic - coastal cod population complexes

The Atlantic cod (Gadus morhua) is a highly mobile species found in an open, marine habitat with no obvious dispersal barriers. Despite this fact, our recent population genetics work has shown that coastal Skagerrak cod is structured into local population s. This observation has opened a whole new set of questions on the genetics, demography and integrity of these coastal populations. Furthermore, we have documented that coastal Skagerrak receives larvae of North Sea origin and that this larval drift coinc ides with the strength of ocean currents. What are the consequences, genetically and ecologically of this larval drift for the coastal populations? Do the North Sea larvae settle and mix with coastal populations? Do North Sea cod utilize coastal waters as nursery areas, returning to the North Sea as adults? Clarifying these issues should be of immediate interest, given the current depleted state of the cod populations in the North Sea. This proposed project aims to understand the structuring and dynamics of coastal populations of cod along the Norwegian Skagerrak coast, and their link to North Sea cod. We will take advantage of existing time series on both mark-recapture data and catch-per-unit-effort data that have so far not been analysed. We will also expand on established genetical techniques and collect cod in coastal habitats and statistically assign them to population of origin (coastal or oceanic). We will merge these genetic techniques with mark-recapture techniques and catch-per-unit-effort meth odology to test for differences in demography among cod of different origin. We will sample both sheltered, fjord habitats and more exposed habitats in the outer skerries. Contrary to the prevailing view, new observations suggest that exposed areas serve as important nursery habitats. A working hypothesise is that there is a gradient in coastal Skagerrak, where cod of North Sea origin are more common in the skerries and locally produced cod dominate within fjord