Cod in fjords and coastal waters of North Norway: distribution and variation in length and maturity at age

Abstract

Abstract The distribution of cod along the Norwegian coast and in fjords from 62°N north to the Russian border was examined using data from annual trawl surveys carried out between 1995 and 2001. Based on differences in growth zones of the otoliths, cod are traditionally classified into two types: Northeast Arctic cod and coastal cod. Both types were found throughout the area investigated. The catch rate of both increased northwards and from offshore to inshore. In a statistical model of length at age, abiotic factors such as area and year of capture explained more of the variance than biotic factors such as sex, stage of maturity, and type of cod. Length at age increased in a southward direction and was higher for cod captured offshore than for those captured inshore. In a statistical model of the proportion mature at age, area, type, and year of capture explained more of the variance than sex and depth of capture. On average, coastal cod attained 50% maturity (M50) more than a year younger than a year younger than Northeast Arctic cod attained maturity. Although there were relatively large differences in age at maturity between neighbouring areas, age at maturity was lowest in the south and inshore, and in general, lower inshore than offshore. As genetic analysis clearly indicates that cod in the study area consist of at least two genetically separated stocks, it is likely that the differences found here in age at M50 might have a genetic component.