This study examined whether simple indicators of condition in individual Atlantic cod (Gadus morhua) are related to biochemical composition and energy content for the whole range of conditions potentially observed in natural populations. The energy content of muscle was largely associated with its protein content, while liver energy content mainly consisted of lipids. Accurate predictions of muscle and liver energy content can also be made from the measurement of their water content. Relationships between energy content, water content, and simple measures such as condition factor and hepatosomatic index provide a fast and accurate assessment of seasonal changes in total available energy reserves in cod. These indices could advantageously be used to monitor the status and recovery of cod stocks and to ensure improved management of that resource. Résumé: Dans cette étude, nous relions des indicateurs simples de la condition des morues franches (Gadus morhua) à leur composition biochimique et leur contenu énergétique et ce pour tous les niveaux de condition pouvant être observés en conditions naturelles. Le contenu en énergie du muscle est largement associé à son contenu en protéines alors que celui du foie est essentiellement relié à son contenu en lipides. Les contenus en protéines du muscle et en lipides du foie sont fortement correlés au contenu énergétique de leur tissu respectif. Des prédictions très précises du contenu énergétique du muscle et du foie peuvent être obtenues par une simple mesure de leur contenu en eau. Les relations qui existent entre les contenus en eau et en énergie ainsi que des mesures simples de condition tel le facteur de condition et l'indice hépato-somatique sont un outil précis et rapide pour mesurer et monitorer les changements saisonniers dans les réserves d'énergie de la morue. Ces indices pourraient avantageusement être utilisés pour suivre l'état et le rétablissement des stocks de morue et assurer une meilleure gestion de cette ressource.

The influence of a lower condition on reproductive investment, somatic energy losses, and postspawning condition of Atlantic cod (Gadus morhua) was examined under the hypothesis that females, in response to lower available energy reserves, would reduce reproductive investment in order to limit somatic energy losses. Laboratory experiments revealed that female cod with high prespawning condition factors ended reproduction in better condition than females with low prespawning condition factors. Fecundity and total egg dry weight were significantly lower in poorcondition females. The loss in somatic mass and energy in these poor-condition females was nevertheless higher, in relative terms, than the losses experienced by females in good condition. Consequently, energy reserves invested in reproduction by poor-condition females increase their risk of mortality. In the northern Gulf of St. Lawrence during the early 1990s, reproductive females had lower fecundities and were in worse prespawning and postspawning condition. The condition of spent females suggested a greater impact of changes in environmental conditions on adult than on immature cod. Reproductive potential and possibly recruitment may have suffered from that situation and could have contributed to the failure of that stock to recover despite the moratorium on commercial fishing.Résumé : L'influence d'une baisse de la condition sur l'effort reproducteur, les pertes d'énergie somatique et le niveau de condition post-frai de la morue franche (Gadus morhua) a été examinée sous l'hypothèse qu'en réponse à une diminution des réserves d'énergie disponibles les femelles vont réduire leur investissement reproducteur dans le but de limiter leurs pertes d'énergie somatique. Des expériences en laboratoire ont révélé que les morues femelles dont le niveau de condition est élevé avant le frai terminent la reproduction en meilleure condition que celles dont le niveau de condition est faible. La fécondité et le poids sec total des oeufs produits sont plus faibles chez les femelles en mauvaise condition. Les pertes en masse et en énergie somatique chez les femelles en mauvaise condition sont néanmoins relativement plus élevées que les pertes encourues par les femelles en bonne condition. Conséquemment, les réserves d'énergie investies dans la reproduction par les femelles en mauvaise condition augmentent leur risque de mortalité. Dans le nord du golfe du St-Laurent au début des années 1990, les femelles reproductrices étaient moins fécondes et en moins bonne condition avant et après le frai. Le niveau de condition post-frai des femelles suggère que l'impact du changement dans les conditions environnementales a été plus important chez les morues adultes que chez les morues immatures. Le potentiel reproducteur et possiblement le recrutement pourraient avoir souffert de cette situation et pourraient avoir contribué à ralentir le rétablissement de ce stock en dépit du moratoire sur la pêche commerciale. Lambert and Dutil 825

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Interannual variations and seasonal cycles in condition and energy reserves were investigated for the northern Gulf of St. Lawrence cod (Gadus morhua) before and during the collapse of the stock. Significant decreases in cod condition between the late 1980s and the early 1990s coincided with the reduction in biomass. Cod exhibited clear seasonal variations in condition factor (Fulton's K), energy reserves, and tissue composition. Maximum K (0.87-0.91) and highest hepatosomatic index (HSI; 4.3-5.7%) occurred during the autumn while minimum levels occurred in spring. In May, the levels of condition (K, 0.69-0.74; HSI, 2.2-3.0) were below those reported for other stocks. In spring during spawning, a proportion of the wild cod had condition and energy reserves that were within the range that resulted in mortality among unfed fish held in the laboratory. Feeding experiments also indicate that the condition of wild cod in fall was lower than that observed for well-fed fish held in the laboratory. The decline in the condition and energy reserves of cod during several consecutive years may have lowered the productivity of the northern Gulf of St. Lawrence stock. This, along with overfishing, could have contributed to the collapse of this stock.

We critically review four potential causes of a drastic decline in juvenile American eels, Anguilla rostrata, recruiting to Lake Ontario (81-fold decline from 1985 to 1992) and in juvenile eel densities in tributaries to the Gulf of St. Lawrence. Silver eels from the St. Lawrence River were much more contaminated and had a high prevalence of deformities and lesions than a reference stock although they were on average less contaminated in 1990 than in 1982 (1.12 versus 4.54 μgg−1 for PCB; 0.025 versus 0.07 μg∙g−1 for mirex). Lethal toxicity from chemical contamination has been known to occur in St. Lawrence River eels for the past 25–30 yr. Major habitat modifications in the St. Lawrence took place in the 1950's (St. Lawrence Seaway and hydroelectric dams), about 30 yr before recruitment started declining; this long delay argues against these perturbations being primary causes of the decline. There is little evidence that commercial fishing and oceanographic changes caused the decline. Overall, we conclude that we do not know what caused the pronounced recruitment decline. We propose research avenues and hypotheses that may advance understanding and emphasize that because of panmixia, the recruitment decline could be species wide.