Life history of fjord cod from the Skagerrak in the mid-2000s compared to 1905

Abstract

Life history changes serve as stress indicators in harvested populations. Data from recent decades show that many species of marine fish are now maturing at younger ages and smaller sizes, associated with a general increase in harvest intensity. However, data from earlier times are generally sparse or lacking. In this study we compare present life history characteristics of fjord cod Gadus morhua in the Skagerrak, southern Norway, to century-old (1905) scientific data. Contrary to our expectations, age and length distributions were shifted towards older and larger fish in the most recent data set compared to the historic sample. Also, fish in the historic sample tended to be smaller at age and reached 50% maturity at a smaller size and younger age compared to the present sample. These results are in contrast to most other studies on life history changes in harvested fish.