Egg production of Baltic cod (Gadus morhua) in relation to variable sex ratio, maturity, and fecundity

Abstract

Observed fluctuations in relative fecundity of Eastern Baltic cod (Gadus morhua L.) were related to food availability during the main feeding period and were used to develop a predictive model that explained 72% of the interannual variations in fecundity. Time series of sex ratios, maturity ogives, and relative fecundity were combined with mean weights-at-age and stock sizes from an analytical multispecies model to estimate the potential egg production (PEP). Relationships between PEP and independent estimates of realized daily and seasonal egg production from egg surveys were highly significant. The difference between estimates of potential and realized seasonal egg production was of a magnitude corresponding to the expected loss of eggs as a result of atresia, fertilization failure, and early egg mortality. The removal of interannual variability in sex ratio, maturity, and fecundity on estimates of PEP deteriorated the relationships in all three cases. PEP proved to be superior to spawning stock biomass as measure of the reproductive potential in a stock-recruitment relationship of Eastern Baltic cod. PEP in combination with the reproductive volume explained 61% of the variation in year-class strength at age 2.Résumé : Les fluctuations observées dans la fécondité relative de la morue franche (Gadus morhua L.) dans l'est de la Baltique ont pu être reliées à la disponibilité de la nourriture durant la période principale d'alimentation et elles ont servi à établir un modèle prédictif qui explique 72 % de la variation de la fécondité d'une année à une autre. Des sé-ries temporelles des rapports mâles:femelles, des ogives de maturité et de la fécondité relative combinées à des données de masses moyennes pour un âge donné et de taille des stocks obtenues d'un modèle analytique multispécifique ont permis d'estimer la production potentielle d'oeufs (PEP). Les relations entre PEP et les estimations indépendantes de production journalière et saisonnière d'oeufs obtenues à partir des inventaires d'oeufs sont hautement significatives. La différence entre les estimations de la production saisonnière potentielle d'oeufs et celles de la production réalisée sont d'un ordre de grandeur qui correspond aux pertes qu'on peut attendre de l'atrésie, de l'absence de fécondation et de la mortalité précoce des oeufs. Le retrait de la variation annuelle du rapport mâles:femelles, de la maturité ou de la fé-condité du modèle d'estimation de PEP affaiblit la relation dans les trois cas. PEP s'avère être une meilleure mesure du potentiel reproducteur que ne l'est la biomasse du stock des reproducteurs dans la relation stock-recrutement de la morue de l'est de la Baltique. PEP, en combinaison avec le volume reproducteur, explique 61 % de la variation de l'importance de la classe d'âge de 2 ans.[Traduit par la Rédaction] Kraus et al. 1920

Linking lipid dynamics with the reproductive cycle in Baltic cod Gadus morhua

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Report of the Workshop on Implementation of Stock Reproductive Potential into Assessment and Management Advice for Harvested Marine Species

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Feasibility of removal of dioxin and dioxin-like PCB's by intensive fishery of herring and sprat in the Baltic Sea

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