Long-term changes in age at sexual maturity of Northeast Arctic cod (Gadus morhua L.)

Maturity ogives for the Northeast Arctic cod for year classes 1923 to 1976 were computed from the age and number of spawning zones in otoliths of cod caught on the spawning grounds at Lofoten. A reduction in the median age at maturity of approximately 2.5 years over the period was found. The change has primarily affected year classes 1950 and later. A reduction in the mean age of the spawning stock by approximately 2.5 years was also found. Males generally matured at a lower age than females, but the difference has become smaller over the period studied. It is suggested that the reduction in median age at maturity is primarily a compensatory response to the reduced stock size. Higher fishing pressure on the late maturing individuals than on the early maturing individuals may also have contributed to the changes, with or without the mediation of genetic changes.