EFFECTS OF EARLY EXPERIENCE ON THE REPRODUCTIVE-PERFORMANCE OF ATLANTIC SALMON

To examine the link between early experience and subsequent reproducti ve performance, we experimentally manipulated the early experience of Atlantic salmon (Salmo salar). Salmon of a common genetic background w ere reared as juveniles either naturally in the river or artificially in a hatchery (sea ranched), depriving them of river experience, and t hen allowed to grow to maturity naturally in the ocean. At maturity th e competitive and reproductive abilities of these fish were compared i n four experiments quantifying reproductive success. Although levels o f aggressive behavior were similar, the experience-deprive; sea-ranche d males were involved in more prolonged aggressive encounters and incu rred greater wounding and mortality than wild males. Furthermore, sea- ranched males were less able to monopolize spawnings and as a result o btained 51% the reproductive success of wild males across the experime nts. This reproductive inferiority varied directly with the male densi ty and bias in the sex ratio, reflecting the intensity of male breedin g competition, A lower intensity of female than male competition was l ikely responsible for the lack of differences in breeding performance between sea-ranched and wild females. Sea-ranched females, however, pr oduced smaller eggs than wild females, apparently in response to their higher juvenile growth rate. Differences in migratory behavior were a lso apparent, as sea-ranched males and females ascended the River Imsa later than wild fish. Our results indicate that early experience has implications for subsequent adult reproductive performance, affecting the development of specialized skills and traits important not only fo r early life, but also later life.