Influence of Interannual Variations in Winter Sea Temperature on Fecundity and Egg Size in Pacific Herring (Clupea harengus pallasi)

Abstract

Data for 2937 fish, collected from seven locations over five years, were analysed to evaluate the effects of sea temperature and stock biomass on size-specific ovary weight and fecundity at spawning. Ovary weight did not vary significantly between years or locations. Size-specific fecundity was higher in 1983, when coastal waters were abnormally warm because of a strong El Niño – Southern Oscillation event. The effect of location was equivocal: one stock that overwintered in warm water tended to have a higher fecundity. Mean sea temperature between 60 and 90 d before spawning (in spring) best accounted for variations in size-specific fecundity. Temperature may influence fecundity by regulating gonadotropin concentration and consequently pre-ovulatory atresia. We hypothesize that the trade-off between fecundity and egg size is adaptive. A theoretical analysis of the early life history of Pacific herring suggests that, to maximize survival to metamorphosis, egg size should decrease and fecundity increase with temperature when the larval growth rate Q10 is less than the mortality rate Q10. Our model seems to explain the differences in egg size between recruit and repeat spawners, and between stocks of Atlantic herring that spawn in different seasons.