Can body size parameters be used to distinguish the Kattegat cod (Gadus morhua) stock from the North Sea cod stock?

Sammanfattning: Atlantic cod is one of the world´s most important commercial fish stocks and is dependent on fishing regulations for its wellbeing and survival. An important part in fisheries management is information of the stock distribution. This is needed to not cause overestimations that results in heavy overfishing. Here, Kattegat and North Sea male and female cod of the same ages (3- to 5-year-old) were distinguished using body size parameters (length, weight and condition). Parameter differences were evident between some year-classes, but when analysing the whole stock, the variance of the body size parameters was too large and could therefore not be used for stock discrimination. When the body size parameters were analysed by season (caught), the parameter variance decreased. However, not low enough for one to be able to use the parameters for stock separation. Thus, I conclude that the body size parameters length, weight and condition, could not be used to distinguish the Kattegat cod stock from the North Sea cod stock.