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

Abstract

Maturity ogives of the Northeast Arctic cod for the year classes 1932 to 1976 were computed based on 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 is indicated. A similar reduction in mean age of the spawning stock was found. Males generally mature at a lower age than females, but the difference has become smaller over the period studied. The decline in median age at maturity is most marked for the year classes after 1950. A compensatory response to the demographic changes could explain the decline. Genetic changes as a result of selective fishing is also possible, but cannot be evaluated from the present data.