Spatial association of genetically similar Atlantic salmon juveniles and sex bias in spatial patterns in a river

Atlantic salmon ( Salmo salar ) juveniles were electrofished along a 300-m stretch of a river to test for possible associations between genetic similarity and geographical distance between individuals. Multilocus DNA fingerprinting showed that genetically similar juveniles (1–4 years old) were found closer together in the river than less related individuals. However, the association between genetic similarity and geographical distance, although significant, was not strong. This may indicate that factors other than genetic relatedness influence the positioning in the river. A sex bias in the relationship between genetic similarity and geographical distance was caused by a difference between sexually mature and immature males. The study shows that sampling of salmon juveniles should be spread over a wide stretch of the river in order to avoid sampling relatives. Moreover, by including several year classes, the overall degree of genetic similarity is effectively reduced compared with sampling individuals of similar age.