The Atlantic salmon belonging to populations of four rivers in the Murmansk Кegion – the Kola, the Tuloma, the Ponoy and the Varzuga, was the object of the study. The paper investigates the reasons for the population dynamics of re-spawning individuals in the spawning salmon populations in the said rivers by searching for statistically significant relationships between the proportion of re-spawning individuals and abiotic factors. Correlation analysis was used as the mathematical research tool. The authors considered their own and literature data on the timing of downstream migration of kelts and their return to repeat spawning, as well as the age structure of the re-spawning subpopulation. Comparison of interannual changes in the proportion of re-spawning individuals in different populations did not reveal any synchronism in the dynamics of this indicator. This fact suggests there exist factors specific to each population that regulate the number of re-spawning salmon individuals. Further analysis showed that in some cases the proportion of re-spawning individuals demonstrated a weak correlation with water temperature in the sea, in other cases – with temperature and water level in the river. In particular, water level has great influence on the proportion of re-spawning individuals in the Kola and Varzuga rivers, but this influence is alternating: while in the Kola River the number of re-spawning individuals in Atlantic salmon populations is in reased by a high level of flood water, in the Varzuga River, on the contrary, it is decreased by this factor. The explanation lies in the different hydrological characteristics of the rivers: in the shallow Varzuga, high flood leads to ice clogging, which can cause a mass death of kelts. The number of re-spawning salmon depends on the overall state of reproduction: the higher the risk of anthropogenic impact, the smaller the relative number of re-spawning individuals, and the simpler the age structure of the spawning stock.