Recruitment of wild and artificially reared cod (Gadus morhua L.) to the local spawning stock
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A stock enhancement study of coastal cod was initiated in 1983, when 19,002 artificially reared cod fry were tagged and released in the Austevoll region in western Norway. As a part of this program, 3,946 cod fry were released in Osen (60° 4'N 5° 13'E), a local spawning ground in Austevoll. The impact of the released cod to the wild cod population in the Osen area, was estimated from biological and genetic samples taken of released and wild cod in 1984 and in the spawning season in 1986 and 1987, when the released cod were expected to recruit to the spawning stock. The released cod were 26%, 36% and 35% of the 1983-yearclass, caught as juvenile cod in 1984 and on the spawning ground in 1986 and 1987, respectively. The released cod seemed to have had the same recruitment pattern to the spawning stock as wild cod of the same yearclass. Comparison of genetic characters between wild and artificially reared cod demonstrated that a rare allele in the enzyme phosphoglucomutase was not present in the broodstock, and subsequently was lost during the artificial production of fry. However, no genetic changes in the other systems investigated were detected, neither when comparing the reared cod fry with the broodstock, nor during the period from release to recruitment to the spawning stock.