Variability in the annual egg production of hatchery-reared Atlantic cod (Gadus morhua) was determined under stable experimental conditions. Egg size increased with fish age as an approximate step function. Comparing first-and second-time spawners, the variance in egg dry weight was 32% within individuals (i.e., the seasonal effect, the cod being a multiple-batch spawner), 55% between years, and 12% between individuals. In several repeat spawners, the curvature of the seasonal egg size curves showed little difference between years. The seasonal decrease in egg size was typically smaller in recruit spawners than in repeat spawners. There was no empirical evidence to suggest that environmental temperature regulates seasonal variations in egg size. The extent of egg swelling (i.e., the egg dry weight/diameter ratio) indicated a strong genetic component. Investment in ovarian growth was influenced by previous allocations as exemplified by annual, sinusoidal fecundity oscillations. Larger fish showed significantly longer spawning periods. The combined influence of maternal factors and the annual temperature variations noticed in the field during early stages suggests that larger larvae at the onset of feeding are more likely to survive.Résumé : On a déterminé la variabilité de la production annuelle d'oeufs chez des morues de l'Atlantique (Gadus morhua) et élevage dans des conditions expérimentales stables. La taille des oeufs augmentait avec l'âge des poissons en suivant approximativement une fonction en escalier. On a comparé le poids sec des oeufs chez des géniteurs à la première et à la deuxième ponte, ce qui a donné une variance de 32% chez les individus (ce qui correspond à l'effet saisonnier, la morue ayant plusieurs pontes pendant la saison), de 55% entre les années et de 12% entre les individus. Chez plusieurs géniteurs ayant frayé plusieurs fois, la forme des courbes saisonnières de la taille des oeufs n'indiquait que peu de différences d'une année à l'autre. La diminution saisonnière de la taille de ceux-ci était typiquement plus faible chez les nouveaux géniteurs que chez les anciens. Rien ne permet de croire que la température du milieu régule les variations saisonnières de la taille des oeufs. L'importance du gonflement des oeufs (c.-à-d. le rapport poids sec/diamètre de l'oeuf) semblait indiquer l'existence d'un important facteur génétique. L'investissement dans la croissance des ovaires était influencé par des investissements antérieurs similaires, comme le montrent les oscillations annuelles sinusoïdales de la fécondité. Les poissons de plus grande taille présentaient des périodes de ponte significativement plus longues. L'influence combinée de facteurs maternels et des variations de la température annuelle notées sur le terrain au cours des premiers stades indique que les larves qui sont les plus grosses au début de la période d'alimentation ont les plus grandes chances de survie. [Traduit par la Rédaction]
The assumption that spawner biomass is directly proportional to total egg production by fish stocks underlies most spawner-recruit relationships. Despite its importance, this assumption is largely untested. Data describing the reproductive potential of Northeast Arctic (NEA) Atlantic cod (Gadus morhua) were used to test the proportionality assumption for a period showing strong variation in condition and abundance of spawners. At the individual scale, relative fecundity varied with length and condition. This decreases the likelihood that the proportionality assumption is valid. At the stock level, total egg production was estimated (1985-1996) using acoustic estimates of total abundance and demographic information from trawl sampling in combination with year-specific fecundity-length relationships. For NEA cod, spawner biomass estimated by virtual population analysis (VPA) was not proportional to total egg production. Compared with VPA-based estimates of spawner biomass, total egg production is an improved index of recruitment potential because (i) the magnitude of variation observed in total egg production was closer to that observed in recruitment and (ii) the relationship between recruitment at age 1 and total egg production approaches the origin. The results suggest that further progress in explaining recruitment variation will be achieved using more sensitive measures of the true reproductive potential of the stock.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.