Fecundity of Atlantic cod ( Gadus morhua) farmed for stock enhancement in Newfoundland bays

Abstract

In response to the historically low spawning biomass of Atlantic cod ( Gadus morhua) off eastern Newfoundland and Labrador, Canada, we are investigating the feasibility of enhancing recruitment through the release of wild-produced, captively-grown broodstock into bays with resident, inshore spawning populations. Large numbers of small cod can be trapped, their growth and fecundity increased by feeding in captivity, and then released back into the bay where captured. The released cod would augment the wild spawning population. To estimate the potential contribution of released fish to population fecundity, we determined the fecundity of wild cod held in sea cages for several years and fed a naturally available diet. Cod captured in Placentia Bay on the south coast of Newfoundland were fed capelin or herring at 2–3% of their body weight every second or third day for three growth seasons. These farmed fish exhibited potential fecundities twice that of free-living Placentia Bay cod of the same weight or length. Cod captured in Trinity Bay on Newfoundland's eastern shore were fed capelin, herring, or squid to near satiation over four growth seasons. These fish exhibited potential fecundities 2–4 times that of wild Trinity Bay cod of similar size. Greater vitellogenic oocyte production per unit somatic weight in these farmed fish apparently is related to good nutrition provided early in the annual reproductive cycle. Spawning potential represented by the weight of farmed fish released into Newfoundland bays for stock enhancement would be underestimated if fecundity–weight relationships based on data from free-living cod were used.