Growth patterns in the North Sea and western mackerel in Norwegian catches 1960- 85

Length, weight and age in random samples from Norwegian catches of' mackerel from 1960 to 1985 have been reviewed. A standard growth curve was constructed by applying a modified von Bertalanffy equation to all data. The deviation from this curve is largely independent of age for adult mackerel, and may be used as a measure of the growth pattern. In the North Sea area, the length at age has increased gradually by 4-5 cm during this period, while it has been nearly stationary in the western spawning area. The condition has remained stable in this period. The mackerel caught in the North Sea is generally larger at age than the typical Western mackerel, even in the years and seasons when Western mackerel dominated in the cathes in the North Sea. The mixing of two stock components with different growth patterns also makes the use of length distributions as a measure of age distributions questionable