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 s tretch of a river to test for possible associations between genetic similar ity and geographical distance between individuals. Multilocus DNA fingerpri nting showed that genetically similar juveniles (1-4 years old) were found closer together in the river than less related individuals. However, the as sociation between genetic similarity and geographical distance, although si gnificant, was not strong. This may indicate that factors other than geneti c relatedness influence the positioning in the river. A sex bias in the rel ationship between genetic similarity and geographical distance was caused b y a difference between sexually mature and immature males. The study shows that sampling of salmon juveniles should be spread over a wide stretch of t he river in order to avoid sampling relatives. Moreover, by including sever al year classes, the overall degree of genetic similarity is effectively re duced compared with sampling individuals of similar age. (C) 1999 The Fishe ries Society of the British Isles.