Relevance of cod (L.) predation for inter-cohort variability in mortality of juvenile Norwegian spring-spawning herring (L.)

Barros, P., Tirasin, E. M., and Toresen, R. 1998. Relevance of cod (Gadus morhua L.) predation for inter-cohort variability in mortality of juvenile Norwegian springspawning herring (Clupea harengus L.) ‐ ICES Journal of Marine Science, 55: 454‐466 Mortality of juvenile Norwegian spring-spawning herring growing up in the Barents Sea is characterized by a high inter-cohort variability. Variable predation pressure from the north-east Arctic cod stock has been proposed as an explanation, but it has been diYcult to test this hypothesis with actual field data. Data on the abundance of the main fish stocks in the Barents Sea ecosystem, collected by the Institute of Marine Research in Bergen during the period 1983‐1993, were analysed to test this hypothesis. Since capelin has been the major prey of cod during the period investigated, the relationship between herring juvenile mortality and the abundance of cod, capelin and herring was investigated. More than 90% of the inter-cohort variation in mortality of juvenile herring observed during this period was explained by a simple model using the ratio of capelin abundance to the abundance of juvenile cod as the explanatory variable. The relationship is strong enough to warrant using the simple model for improving the short-term forecasts of recruitment to the spawning stock of Norwegian spring-spawning herring. ? 1998 International Council for the Exploration of the Sea