Seasonal dynamics in feeding, organ weights, and reproductive maturation of Atlantic cod (Gadus morhua) in the southern Gulf of St Lawrence

Atlantic cod (Gadus morhua L.) were sampled from the southern Gulf of St Lawrence over a 2-year period (1991-1993) to assess the timing and magnitude of seasonal changes in diet composition, stomach fullness, carcass weight, and organ weights. The proportion of fish (mainly Clupea harengus L. and Mallotus villosus Muller) in the diet of cod was the highest ever reported for this stock. Cod fed very little during the five winter months (December to April) and lost 25-27% of their carcass weight and 74-84% of their liver dry weight during this time. Declines in carcass and liver weights occurred steadily throughout winter and were not specifically coincident with the spring and autumn migrations (approximate one-way distance 500 km) performed by this cod stock. Gonad growth occurred primarily between November and January in males and between January and May in females. Depending on gender and body size, 4-19% of the dry weight lost from the carcass and liver over winter could be accounted for by gonad growth. Therefore, 81-96% of the loss in carcass and liver dry weight over winter was used to meet metabolic energy requirements. The condition factors and hepatosomatic indices of cod in spring were low enough to suggest that winter starvation may cause mortality in this stock. The yield of marketable product (muscle) varied by 39-50% (depending on cod body size) over the course of the study; yields were highest in late autumn and lowest in spring. (C) 1999 International Council for the Exploration of the Sea.