Effects of juvenile nursery on geographic spawning distribution in Norwegian spring-spawning herring (Clupea harengus L.)

Abstract

The Norwegian spring-spawning herring is characterized by a heterogeneous growth pattern originating from nurseries situated along the Norwegian coast and in the Barents Sea. Using a classification algorithm based on measurements of the three first scale annuli, the geographic, temporal, and age dependent recruitment patterns of the coastal and Barents Sea components of most year classes from 1930 to 1989 were studied. The relative importance of each component in the year classes varied with the fluctuating stock size observed during the period studied. In periods with a low spawning stock almost no recruitment appeared from the Barents Sea juvenile areas, while at high stock levels tile Barents Sea component totally dominated the spawning stock. The asynchronous maturation of the two components caused a recruitment pattern characterized by a high proportion of the coastal component at younger ages and an increasing proportion of the Barents Sea component at older ages. Both components recruited along the entire spawning range studied, and once fully recruited, no latitudinal gradient in the spawning stock component composition was observed.