Recruitment variability in Norwegian spring-spawning herring (Clupea harengus L.): the effect of temperature in larval drift trajectories

Abstract

During late winter, the Norwegian spring-pawning (NSS) herring migrate southward along the Norwegian coast to spawn in March-April. The larvae drift northwards in the Norwegian coastal current during their first months and eventually most of the larvae and juveniles end up in the Barents Sea. Here, we have compiled measurements of temperature alon, 0 the coast back to 1936 and analyse these data for correlation with recruitment success (recruits/SSB) of the herring. We find that although the average temperature in the larval drift trajectory may vary with as much as 2°C between years, the effect on recruitment success is minor. A model using temperature-dependent growth and size-dependent mortality predicted a strong relationship between recruitment and the annual temperature variations, but no strong support of this was evident in the data. Nor did we fmd a relation between recruitment success and the condition of the spawning stock, while a strong stockrecruitment rdationship and density-dependent recruitment prevails.