A REVIEW OF HOMING AND STRAYING OF WILD AND HATCHERY-PRODUCED SALMON

This paper reviews studies on the patterns of straying of adult salmon ids from their river or hatchery of origin, with emphasis on Pacific s almon. The prevalence of straying varies greatly among populations. In general, introduced (i.e. non-native) populations and salmon displace d from their rearing site for release stray more than native salmon an d those reared and released on-site. Evidence that standard hatchery p ractices increase the tendency of salmon to stray is equivocal but rel eases of salmon at a different season from the normal migration period can increase straying. Estimates of straying vary greatly between hat cheries and rivers, so general statements on straying proportions have minimal biological significance. Straying between hatcheries and spaw ning grounds gives cause for concern because there is evidence that th e offspring of hatchery-produced salmon may be less viable than those from local wild fish. The impact of straying on local gene pools depen ds not only on the prevalence of straying but on the degree of assorta tive mating and survival differential between populations. At present, fundamental gaps in our understanding of the genetic and environmenta l factors that influence straying hinder accurate prediction of the le vels and consequences of straying.