A study of first-feeding herring (Clupea harengusL.) larvae during the period 1985–1993

Abstract

Since 1987, the spawning stock of Norwegian spring-spawning (Nss) herring has increased from 0.5 to 2.5 million metric tonnes with recruitment of the 1983 year class to the spawning stock. During the same period the increase in herring larval production, resulting from an increase in the spawning stock biomass, has been followed by surveys on the Norwegian shelf in March and April. The purpose of the present study was to investigate whether the number of larvae can be related to spawning stock biomass and to look for density-dependent effects on gut-contents and larval growth. The strong signal from the 5-fold increase in spawning stock biomass was easily seen in the increased abundance of herring larvae since 1988. No density-dependent compensatory mechanisms related to growth were observed; however, a depensatory increase in dry weight was connected to the high abundance of post yolk sac larvae. This must be related to large scale spatial and temporal changes in prey abundance. Co-occurrence of herring larvae and their prey (match) could also be recognized in the early stages by the increased abundance of larvae beyond the yolk sac stage.