Salmon populations from the River Eden in Cumbria, UK, were sampled in the years 1999, 2000 & 2002. A radio-tracking analysis and demographic data revealed gender-specific difference in body-size depending on how long a salmon had spent at sea i.e. their sea-winter tactic. These differences are likely to stem from gender-specific costs in both foraging at sea, and the upstream migration. In addition, gender-specific patterns were observed in the distance a salmon would migrate upstream to spawn, these differences were again dependent on the sea-winter tactic employed by the individual. Females spawn, on average, at different distances upstream depending on their time at sea, no such trend occurs in males. It is hypothesised that this is due to male behaviour being shaped to compete for more mating opportunities, in contrast to female behaviour, which is shaped to seeking out better quality breeding sites. A genetic analysis of adult salmon using 11 microsatellite loci revealed that river geography contributes to population structure. This occurs at both the between-river, and the within-river level (overall F_ST = 0.01). Individual assignment testing revealed gender-specific patterns of dispersal; furthermore, differences were found between the sexes in heterozygosity and allelic richness. Estimations of effective population size were all < 100, well below the level of 500 suggested to counter the deleterious effects of genetic drift. A genetic analysis of juvenile salmon using 10 microsatellite loci found that in the Eden catchment, the within-river component of genetic variation was 10x higher than the between-river component (AMOVA; overall F_ST = 0.048). This suggests that managing salmon on a river-by-river basis may not be appropriate.