Connectivity among subpopulations of Norwegian Coastal cod. Impacts of physical-biological factors during egg stages.

Abstract

Norwegian Coastal cod form a stationary population of Atlantic cod ( Gadus morhua L.) consisting of several genetically separated subpopulations. A small-scale differen- tiation in marine populations with pelagic eggs and larvae is made possible by local retention of early life stages in coastal regions. A numerical model was implemented for a part of the northern Norwegian coast with 800 m horizontal resolution, in addition to two fjord systems with higher resolution; Folda in Nordland and Porsangerfjorden in Finnmark. The model results were used to simulate connectivity and retention of cod eggs among coastal regions and fjords. The cod eggs in Folda attained a subsur- face vertical distribution, avoiding the surface and causing retention. River regulations caused by hydroelectric power production alters the seasonal runoff cycle and reduced the retention of cod eggs in Folda. The dispersion of planktonic organisms in Por- sangerfjorden is highly affected by the local wind and varies with resolution on the atmospheric forcing in the model. Coastal spawning areas have intermediate connec- tivity of early life stages between neighboring areas. High retention of eggs in fjords combined with strong homing to spawning areas indicate that fjord subpopulations may be described as a metapopulation.