Varlation in migration and abundance of norwegian spring spawning herring (Clupea harengusL.)

The Norwegian spring spawning herring has undergone great fluctuations in abundance and changes in migration. In the middle of this century the stock was in a productive phase, after which a serious depletion took place and the stock collapsed by the end of the 1960s. The primary factor for the collapse was high fishing pressure. A gradual, but small increase in the adult stock took place between 1974 and 1986. In this period the adult herring...