LIFE-HISTORY STRATEGIES OF THE SQUID, ILLEX-ILLECEBROSUS, IN THE NORTHWEST ATLANTIC

Time series (1965-1985) of Illex illecebrosus catch and morphometric d ata from the Northwest Atlantic were analysed to describe geographic v ariability in population structure. The areas studied were NAFO sub-ar eas 3 to 6, which range from Newfoundland to the northeastern USA shel f. Population components, reflecting seasonal spawning groups, were id entified based on analysis of length frequency data. Components 3 and 4 represent two prominent life cycles: the summer spawners and winter spawners respectively. Components 1, 2, and 5 do not represent differe nt life cycles, but result from the capacity to shift between life cyc les by prolonging (or shortening) the life span. The presence of up to five components in the southern area illustrates a life history strat egy involving protracted spawning and complex population structure. Th ere was clear geographic variability in annual catch, with fluctuation s being most extreme in the most northern area. Annual catch levels in all areas were significantly correlated with the abundance of the win ter-spawning component, as represented by the number of squid within s amples which belong to component 4. Population structure in the most n orthern area was simplest and catch levels therefore were most depende nt on the highly migratory winter-spawning component. This leads to gr eater catch variability in the most northern area than in the other ar eas. The advantages of good feeding conditions may compensate for the risks associated with long-range migrations, especially recruitment fa ilure. Life history strategies involving migratory and non-migratory p opulation components limit the risk of recruitment failure. The overal l resultant life history strategy for Illex illecebrosus is one that e nsures survival of the species by stabilizing recruitment in at least one (southern) area through protracted spawning, complex population st ructure and interaction of spawning components.