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]

Havforskningsinstituttets institusjonelle arkiv Brage IMR - Institutional repository of the Institute of Marine Research b r a g e i m rDette er forfatters siste versjon av den fagfellevurderte artikkelen, vanligvis omtalt som postprint. I Brage IMR er denne artikkelen ikke publisert med forlagets layout fordi forlaget ikke tillater dette. Du finner lenke til forlagets versjon i Brage-posten. Det anbefales at referanser til artikkelen hentes fra forlagets side. Ved lenking til artikkelen skal det lenkes til post i Brage IMR, ikke direkte til pdf-fil.This is the author's last version of the article after peer review and is not the publisher's version, usually referred to as postprint. You will find a link to the publisher's version in Brage IMR. It is recommended that you obtain the references from the publisher's site.Linking to the article should be to the Brage-record, not directly to the pdf-file.

Life-history theory suggests that animals may skip reproductive events after initial maturation to maximize lifetime fitness. In iteroparous teleosts, verifying past spawning history is particularly difficult; the degree of skipped spawning at the population level therefore remains unknown. We unequivocally show frequent skipped spawning in Northeast Arctic cod (NEAC) in a massive field and laboratory effort from 2006 to 2008. This was verified by postovulatory follicles in temporarily arrested ovaries close to the putative spawning period. At the population level, "skippers" were estimated to be approximately equally abundant as spawning females in 2008, constituting ∼24% of the females 60-100 cm. These females never truly started vitellogenesis and principally remained on the feeding grounds when spawners migrated southward, avoiding any migration costs. The proximate cause of skipping seems to be insufficient energy to initiate oocyte development, indicating that skipped spawning may partly be a density-dependent response important in population regulation. Our data also indicate more skipping among smaller females and potential tradeoffs between current and future reproductive effort. We propose that skipped spawning is an integral life-history component for NEAC, likely varying annually, and it could therefore be an underlying factor causing some of the currently unexplained large NEAC recruitment variation. The same may hold for other teleosts.codfish | population dynamics | reproductive biology | total egg production | stock reproductive potential P opulation demography changes according to reproduction and mortality. In high latitude marine ectotherms, including teleosts, survival of the youngest age classes varies substantially, resulting in large fluctuations in population size (1). Historic spawning stock biomass (SSB) is used to forecast future fish recruitment, although the amount of unexplained variation indicates that SSB may not accurately reflect offspring production (2, 3). One factor that could significantly impact egg production is skipped spawning-the failure of iteroparous spawners to use each spawning opportunity after sexual maturity sensu (4). For most teleosts this phenomenon and its impact on population demography has received scant attention, but theoretical models indicate that up to 30% of the mature individuals may skip spawning and that it is an adaptive strategy optimizing lifetime fitness (5). To date, skipped spawning has been documented in more than 30 species (4, 6), including freshwater (7), marine (8), and anadromous teleosts (9). It has been documented for fish with both indeterminate and determinate fecundity and sequential hermaphrodites (6) and in species with as diverse life histories as the European horse mackerel Trachurus trachurus (10) and the orange roughy Hoplostethus atlanticus (8). Given the difficulty in conclusively establishing past spawning, reports of skipped spawning in teleosts are commonly anecdotal (4).The major process of energy transfer and oocyte gr...

Havforskningsinstituttets institusjonelle arkiv Brage IMR - Institutional repository of the Institute of Marine Research b r a g e i m rDette er forfatters siste versjon av den fagfellevurderte artikkelen, vanligvis omtalt som postprint. I Brage IMR er denne artikkelen ikke publisert med forlagets layout fordi forlaget ikke tillater dette. Du finner lenke til forlagets versjon i Brage-posten. Det anbefales at referanser til artikkelen hentes fra forlagets side. Ved lenking til artikkelen skal det lenkes til post i Brage IMR, ikke direkte til pdf-fil.This is the author's last version of the article after peer review and is not the publisher's version, usually referred to as postprint. You will find a link to the publisher's version in Brage IMR. It is recommended that you obtain the references from the publisher's site.Linking to the article should be to the Brage-record, not directly to the pdf-file. Abstract 10To examine mechanisms that affect fecundity, atresia and skipped spawning in Northeast 11Arctic cod (Gadus morhua L.), we conducted an experiment where wild-caught cod (>60 cm) 12 kept under restricted food regimes were subjected to monthly biopsies, hormonal and physical 13 measurements. The power of body weight as a fecundity proxy increased until the presumed 14 end of follicle proliferation in early November, thereafter it remained stable. Atresia occurred 15 in most females; but, for maturing females, mainly close to spawning. 18 % of the females 16 had small gonads with predominantly previtellogenic oocytes at sacrifice in January. These 17 females were past-spawners, verified by post ovulatory follicles in their gonadss. These 18 "skippers" had lower condition than maturing cod from December, smaller livers upon 19 sacrifice and lower plasma 17-β estradiol values from early November. Until November, 20 oocytes developed similarly for all females, but in November oocyte development was 21 arrested at the early cortical alveoli stage and atresia occurred in all skippers. In sum, 22 fecundity and skipped spawning seem highly influenced by energy reserves during early 23 vitellogenesis and limited to females only. Finally, skippers were identifiable long before the 24 predicted onset of spawning, which could have implications for forecasting of egg production 25 and hence stock-recruitment relationships. 26