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

Abstract

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-yearold parrs for each of three consecutive years for nine genetically distinct populations (total n = 2506) from Québec, 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 .

Estimating the effective number of breeders from single parr samples for conservation monitoring of wild populations of Atlantic salmon Salmo salar

“…For population monitoring purposes, either in the context of a LITS or for point evaluation of management practices, comparison of N b estimates through time and space [control v . treatment comparison (Ozerov et al, )] or between populations [evaluating the effect of stocking (Perrier et al, )], several factors should be considered during sampling design as demonstrated herein. First, sampling time of year should be the same across years and populations, because it is sensitive to time of sampling as N b accounts for YOY survival until sampling.…”

“…There was no significant correlation between N b and N c across 10 years in the River Nivelle. Indeed, N b and N c did not co‐vary across years leading to high inter‐annual variation of N b : N c as previously reported for the species (Palstra et al, ; Ferchaud et al, ; Perrier et al, ). This typical variation in N b : N c in combination with lack of correlation between N b and N c may indicate that variance in reproductive success could be an important factor in N b variation in this population, in addition to the number of individuals that effectively reproduced (Luikart et al, ).…”

“…In this context, genetic monitoring of effective population size has been recognized as a complementary resource for conservation planning (Dodson et al, ). Routine implementation in population management, however, has not followed, probably due to the continuous development of refined methods over the past decade (Wang et al, ) and the limited number of studies showcasing practical applications in the context of population management (but see Ozerov et al, ; Whiteley et al, ; Ferchaud et al, ; Perrier et al, for recent examples). A second objective of this study is to bridge the gap between academia and resource management practice.…”

Effective number of breeders, effective population size and their relationship with census size in an iteroparous species,Salvelinus fontinalis

“…R. Soc. B 283: 20152601 phenomenon and is a function of variation in the effective number of breeders (see also [14,39,43]) and in reproductive success. In fact, given the estimated age-specific survival rates and age-or size-specific relative frequencies, we have shown with AGENE [34] that very high variances in reproductive success (between 50 and 100 times higher than the mean reproductive success) are necessary to generateN e =N c in the 0.05-0.02 range (200 times higher to generate ratios % 0.01).…”

Effective size of density-dependent populations in fluctuating environments

“…They attributed this to decreased variance in reproductive success at small population sizes ( see also Hedrick ; Perrier et al. ) and suggested several biological explanations, such as higher fraction of reproducing individuals in small populations, a decrease in competition for mates or a decrease in embryo mortality. In the current study, neither annual nor lifetime variance in reproductive success decreased as N decreased.…”