Buoyancy and vertical distribution of Norwegian coastal cod (Gadus morhua) eggs from different areas along the coast

There are significant genetic differences in coastal cod (Gadus morhua) along the Norwegian coast, and in order to maintain these differences, there must be mechanisms that ensure local retention of eggs and larvae in the spawning areas. The buoyancy of eggs from four different areas along the Norwegian coast was measured using a density gradient column, and the results from modelling experiments showed that in three of the groups (Tysfjord, Helgeland, and Oygarden), the buoyancy in combination with local hydrography would place the eggs in subsurface waters where retention is greater than in surface waters.