Effects of early experience on the reproductive performance of Atlantic salmon

To examine the link between early experience and subsequentreproductive performance, we experimentally manipulated theearly experience of Atlantic salmon (Salmo salar). Salmon ofa common genetic background were reared as juveniles eithernaturally in the river or artificially in a hatchery (sea ranched),depriving them of river experience, and then allowed to growto maturity naturally in the ocean. At maturity, the competitiveand reproductive abilities of these fish were compared in fourexperiments quantifying reproductive success. Although levelsof aggressive behavior were similar, the experience-deprived,sea-ranched males were involved in more prolonged aggressiveencounters and incurred greater wounding and mortality thanwild males. Furthermore, sea-ranched males were less able tomonopolize spawnings and as a result obtained 51% the reproductivesuccess of wild males across the experiments. This reproductiveinferiority varied directly with the male density and bias inthe sex ratio, reflecting the intensity of male breeding competition.A lower intensity of female than male competition was likelyresponsible for the lack of differences in breeding performancebetween sea-ranched and wild females. Sea-ranched females, however,produced smaller eggs than wild females, apparently in responseto their higher juvenile growth rate. Differences in migratorybehavior were also apparent, as sea-ranched males and femalesascended the River Imsa later than wild fish. Our results indicatethat early experience has implications for subsequent adultreproductive performance, affecting the development of specializedskills and traits important not only for early life, but alsolater life.