| Summary: | The catch, distribution, and biology were studied in Norwegian spring spawning herring during the spawning season in 1995. Both the spawning time and choice of spawning grounds were influenced by the size and condition of the fish. The stock wintered in Vestfjorden, northern Norway, and spawning grounds were utilized southwards along the coast within a range of 1500 km. The herring arrived the spawning grounds in a decreasing order of length and condition. This was mainly due to size specific swimming speed and not size specific maturation. Delayed maturation with fish length was only found within the recruits, which spawned in a second wave. In addition, the size and condition of the fish in a spawning area increased southwards, and there was a delayed spawning and prolonged spawning period at the northernmost spawning grounds. We suggest that life-history theory explains the observed spawning distribution. Individuals must consider trade off between migration distance, reproductive output, own survival and larval survival based on their body size and condition.
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