Effective number of breeders in relation to census size as management tools for Atlantic salmon conservation in a context of stocked populations

Monitoring short-term fluctuations in effective population sizes (N-e) and effective number of breeders (N-b), as well as their ratio to adult census population size (N-e/N-c and N-b/N-c), provide insight into population demography and inform conservation programs towards limiting long-term loss of evolutionary potential in wild populations. In this study, we monitored short-term variations of N-b and N-b/N-c over three consecutive years for nine Atlantic salmon populations from Quebec, Canada. We documented how these population genetic parameters were influenced by anadromous population size as well as yearly and long-term stocking intensity. Towards this end, 15 microsatellites were used to genotype about 100 one-year-old parrs for each of three consecutive years for nine genetically distinct populations (total n = 2506) from Qubec, Canada. Yearly stocking intensity had a negative effect on N-b/N-c, possibly as a consequence of a reduced reproductive contribution of stocked relative to wild fish. However, the impact of long-term stocking intensity on N-b/N-c was not significant, which may indicate relatively weak carry-over effects of stocking on future generations. Also, N-b/N-c was negatively correlated with N-c, suggesting compensatory mechanisms, as previously reported in other salmonids. Overall, this study provides evidence of relatively weak and short-term effect of stocking on N-b/N-c ratio in Atlantic salmon populations and suggests potential biological mechanisms leading to the significant negative relationship between N-b/N-c and N-c.