Pattern and variability in the breeding system of Atlantic salmon (Salmo salar), with comparisons to other salmonids

The breeding system of Atlantic salmon (Salmo salar) is shaped both by natural selection for offspring production and by sexual selection for access to mating opportunities. These evolutionary forces operate with differing intensities in the two sexes to shape their breeding behaviour and tactics. Female breeding success is largely dependent on egg production, access to breeding territories, and nest quality and survival. By contrast, male breeding success is largely determined by access to ovipositing females. As such, the breeding system of Atlantic salmon is similar to that of other members of the subfamily Salmoninae. However, early male maturity, a common pattern within the Salmoninae, reaches its greatest expression in both terms of frequency and magnitude of the mature male size difference in Atlantic salmon. Despite generalities, spawning populations of Atlantic salmon are not static, as they exhibit spatial and temporal variability in demography (e.g., spawner density, sex ratio, age at maturity, and body size). Events, both natural and anthropogenic (e.g., exploitation, habitat alteration, and climatic changes), affect this variability and ultimately shape the breeding system.