Abstract
Abstract Current methods of stock assessment using plankton surveys and fecundity measurements are based on the assumption that the western mackerel (Scomber scombrus L.) has a determinate fecundity, that is, the number of oocytes destined to be matured in a season is decided prior to spawning and can be identified and counted before release of the first egg batch. This assumption has been questioned in recent years and the possibility of a serious miscalculation of fecundity has been raised. Evidence presented here shows that: A hiatus does not develop in the size frequency distribution between the previtellogenic and vitellogenic oocytes prior to spawning. The number of vitellogenic oocytes (potential annual fecundity) declines during spawning. The agreement between the potential annual fecundity measured prior to spawning and the number of eggs shed during spawning calculated by estimating the size and frequency of egg batches and the duration of the spawning season is somewhat ambiguous. The productio...
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