The genetic consequence of hatchery-rearing on life-history traits of the Atlantic salmon (Salmo salar L): a comparative analysis of sea-ranched salmon with wild and reared parents

We examined the influence of parental breeding history (wild or hatchery-reared and released) and the parental sea-age of Atlantic salmon (Salmo salar L.) on the life-history traits of the subsequent sea-ranched generation. The progeny of mating groups with different parental breeding histories and parental sea-ages were compared. During the experiment, 22000 2-year-old tagged smelts were released into the estuary of the River Kemijoki, in 1986 and 1988. The total recovery rate of the released smelts was over 10%. The sea growth rate of progeny was not independent of parental traits, breeding history or female or male sea-age. The progeny of ranched parents grew more rapidly in the sea than did the progeny of wild parents. Nor was sea-age at maturity of progeny independent of parental traits. The model, in which sea-age at maturity of progeny was dependent on the parental breeding history, but not on female sea-age, fitted the data well (P = 0.535). The ranched parents produced more mature grilse (52%) than did wild parents (37%; P = 0.026). The tests of independence revealed that sea-age at maturity of progeny was dependent on male sea-age (P = 0.670) more than on female sea-age (P = 0.178). However, the annual age distributions of offspring captured during the spawning migration were similar to those of parental sea-age groups. The progeny of three-sea-winter (3SW) ranched females were larger after two sea-growth periods and were captured relatively more often in the northern Main Basin than were the progeny of ranched two-sea-winter (2SW) females. These results support the hypothesis that different selective factors, whether intentional or unintentional, and domestication effects during the parental juvenile period change the genetic characteristics of growth and sea-age at first maturity. However, parental sea-age also had a genetic influence on the progeny. Maintenance of viable and genetically variable sea-ranched salmon stocks in the Baltic present a great challenge today and will continue to do so in the future. (C) 1997 Elsevier Science B.V.