Increasing the spawning biomass of northern Atlantic cod, Gadus Morhua, through the release of mature farmed fish

Hiscock, H. Wade (Harris Wade) (1997) Increasing the spawning biomass of northern Atlantic cod, Gadus Morhua, through the release of mature farmed fish. Masters thesis, Memorial University of Newfoundland.

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Abstract

It may be possible to increase annual recruitment to the northern Atlantic cod, Gadus morhua, stock through enhancement of the spawning biomass. For marine fish species whose fecundities are a function of body size, such as cod, it may be possible to increase the growth of wild fish in sea cages to artificially advance their fecundity. One objective was to determine if cod from Trinity Bay, Newfoundland could have significant gains in fecundity after being fed in captivity, compared to noncaptive fish. A second objective was to determine if captivity affected the survival of cod once released back into the sea. Cod held in captivity for nearly four years (1992-96) and fed to satiation every 2-3 days (over four growth seasons from May - October) were significantly larger at age than wild fish, and consequently had 2-4 fold higher potential fecundity. Spawning occurred in the sea cages over a period of ~ 60 days, coincident with the spawning period observed for wild cod in Trinity Bay. Farmed cod produced fertilized eggs and viable larvae. Farmed cod seemed to adopt a normal free-living behaviour after release, as evident from sonic tracking and tag-recapture data. However, for several months after release, farmed fish experienced a higher fishing mortality than a control wild group.

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