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A major challenge in understanding the response of populations to climate change is to separate the effects of local drivers acting independently on specific populations, from the effects of global drivers that impact multiple populations simultaneously and thereby synchronize their dynamics. We investigated the environmental drivers and the demographic mechanisms of the widespread decline in marine survival rates of Atlantic salmon (Salmo salar) over the last four decades. We developed a hierarchical Bayesian life cycle model to quantify the spatial synchrony in the marine survival of 13 large groups of populations (called stock units, SU) from two continental stock-groupings (CSG) in North America (NA) and Southern Europe (SE) over the period 1971-2014. We found strong coherence in the temporal variation in post-smolt marine survival among the 13 SU of NA and SE. A common North Atlantic trend explains 37% of the temporal variability of the survivals for the 13 SU and declines by a factor 1.8 over the 1971-2014 time series. Synchrony in survival trends is stronger between SU within each CSG. The common trends at the scale of NA and SE capture 60% and 42% of the total variance of temporal variations, respectively. Temporal variations of the post-smolt survival are best explained by the temporal variations of sea surface temperature (SST, negative correlation) and net primary production indices (PP, positive correlation) encountered by salmon in common domains during their marine migration. Specifically, in the Labrador Sea/Grand Banks for NA populations 26% and 24% of variance is captured by SST and PP, respectively and in the Norwegian Sea for SE populations 21% and 12% of variance is captured by SST and PP, respectively. The findings support the hypothesis of a response of salmon populations to large climate induced changes in the North Atlantic simultaneously impacting populations from distant continental habitats.

Fisheries targeting mixtures of populations risk the overutilization of minor stock constituents unless harvests are monitored and managed. We evaluated stock composition and exploitation of Atlantic salmon (Salmo salar) in a subsistence fishery in coastal Labrador, Canada, using genetic mixture analysis and individual assignment with a microsatellite baseline (15 loci, 11 829 individuals, 12 regional groups) encompassing the species’ western Atlantic range. Bayesian and maximum likelihood mixture analyses of fishery samples over 6 years (2006–2011; 1772 individuals) indicate contributions of adjacent stocks of 96%–97%. Estimates of fishery-associated exploitation were highest for Labrador salmon (4.2%–10.6% per year) and generally <1% for other regions. Individual assignment of fishery samples indicated nonlocal contributions to the fishery (e.g., Quebec, Newfoundland) were rare and primarily in southern Labrador, consistent with migration pathways utilizing the Strait of Belle Isle. This work illustrates how genetic analysis of mixed stock Atlantic salmon fisheries in the Northwest Atlantic using this new baseline can disentangle exploitation and reveal complex migratory behaviours., En l’absence de surveillance et de gestion des prises, les pêches qui ciblent des mélanges de populations posent un risque de surutilisation de stocks mineurs. Nous avons évalué la composition et l’exploitation des stocks de saumons atlantiques (Salmo salar) dans une pêche de subsistance sur la côte du Labrador (Canada) par l’analyse des mélanges génétiques et l’affectation d’individus à la lumière de données microsatellitaires de référence (15 microsatellites, 11 829 individus, 12 groupes régionaux) couvrant l’aire de réparation de l’espèce dans la partie ouest de l’océan Atlantique. Les analyses bayésiennes et de maximum de vraisemblance de mélanges d’échantillons tirés de cette pêche sur une période de 6 ans (2006–2011, 1772 individus) indiquent que les stocks adjacents constituent de 96 % à 97 % de cette pêche. Les estimations de l’exploitation associée à cette pêche étaient les plus élevées pour le saumon du Labrador (de 4,2 % à 10,6 % par année) et généralement <1 % pour le saumon d’autres régions. L’affection des individus des échantillons de la pêche indiquait que les contributions non locales à cette pêche (p. ex. de Québec ou Terre-Neuve) étaient rares et principalement limitées au sud du Labrador, ce qui concorde avec les voies de migration passant par le détroit de Belle-Isle. L’étude illustre comment l’analyse génétique de pêches au saumon atlantique de stocks mélangés dans le nord-ouest de l’Atlantique à la lumière de la nouvelle base de données de référence peut permettre de discriminer l’exploitation des différents stocks et révéler des comportements migratoires complexes.

Interceptory fisheries represent an ongoing threat to migratory fish stocks particularly when managed in the absence of stock specific catch and exploitation information. Atlantic salmon from the southern portion of the North American range may be subject to exploitation in the commercial and recreational salmon fisheries occurring in the French territorial waters surrounding St. Pierre and Miquelon off southern Newfoundland. We evaluated stock composition of Atlantic salmon harvested in the St. Pierre and Miquelon Atlantic salmon fishery using genetic mixture analysis and individual assignment with a microsatellite baseline (15 loci, 12,409 individuals, 12 regional groups) encompassing the species western Atlantic range. Individual salmon were sampled from the St. Pierre and Miquelon fishery over four years (2004, 2011, 2013, and 2014). Biological characteristics indicate significant variation among years in the size and age distribution. Nonetheless, estimates of stock composition of the samples showed consistent dominance of three regions (i.e., Southern Gulf of St. Lawrence, Gaspe Peninsula, and Newfoundland). Together salmon from these regions accounted for more than 70% of annual harvest over the decade examined. Comparison of individual assignments and biological characteristics revealed a trend of declining fresh water age with latitude of assigned region. Moreover, locally harvested Newfoundland salmon were ten times more likely to be small or one sea winter individuals whereas Quebec and Gaspe Peninsula salmon were two-three times more likely to be harvested as large or two sea winter salmon. Estimates of region specific catch were highest for salmon from the southern Gulf of St. Lawrence region ranging from 242 to 887 individuals annually. This work illustrates how genetic analysis of interceptory marine fisheries can directly inform assessment and management efforts in highly migratory marine species., Keywords: Mixed-stock analysis Genetic assignment Atlantic salmon Genetic structure Microsatellites

Interceptory fisheries represent an ongoing threat to migratory fish stocks particularly when managed in the absence of stock specific catch and exploitation information. Atlantic salmon from the southern portion of the North American range may be subject to exploitation in the commercial and recreational salmon fisheries occurring in the French territorial waters surrounding St. Pierre and Miquelon off southern Newfoundland. We evaluated stock composition of Atlantic salmon harvested in the St. Pierre and Miquelon Atlantic salmon fishery using genetic mixture analysis and individual assignment with a microsatellite baseline (15 loci, 12,409 individuals, 12 regional groups) encompassing the species western Atlantic range. Individual salmon were sampled from the St. Pierre and Miquelon fishery over four years (2004, 2011, 2013, and 2014). Biological characteristics indicate significant variation among years in the size and age distribution. Nonetheless, estimates of stock composition of the samples showed consistent dominance of three regions (i.e., Southern Gulf of St. Lawrence, Gaspe Peninsula, and Newfoundland). Together salmon from these regions accounted for more than 70% of annual harvest over the decade examined. Comparison of individual assignments and biological characteristics revealed a trend of declining fresh water age with latitude of assigned region. Moreover, locally harvested Newfoundland salmon were ten times more likely to be small or one sea winter individuals whereas Quebec and Gaspe Peninsula salmon were two-three times more likely to be harvested as large or two sea winter salmon. Estimates of region specific catch were highest for salmon from the southern Gulf of St. Lawrence region ranging from 242 to 887 individuals annually. This work illustrates how genetic analysis of interceptory marine fisheries can directly inform assessment and management efforts in highly migratory marine species., Keywords: Mixed-stock analysis Genetic assignment Atlantic salmon Genetic structure Microsatellites

Fisheries targeting mixtures of populations risk the overutilization of minor stock constituents unless harvests are monitored and managed. We evaluated stock composition and exploitation of Atlantic salmon (Salmo salar) in a subsistence fishery in coastal Labrador, Canada, using genetic mixture analysis and individual assignment with a microsatellite baseline (15 loci, 11 829 individuals, 12 regional groups) encompassing the species’ western Atlantic range. Bayesian and maximum likelihood mixture analyses of fishery samples over 6 years (2006–2011; 1772 individuals) indicate contributions of adjacent stocks of 96%–97%. Estimates of fishery-associated exploitation were highest for Labrador salmon (4.2%–10.6% per year) and generally <1% for other regions. Individual assignment of fishery samples indicated nonlocal contributions to the fishery (e.g., Quebec, Newfoundland) were rare and primarily in southern Labrador, consistent with migration pathways utilizing the Strait of Belle Isle. This work illustrates how genetic analysis of mixed stock Atlantic salmon fisheries in the Northwest Atlantic using this new baseline can disentangle exploitation and reveal complex migratory behaviours., En l'absence de surveillance et de gestion des prises, les pêches qui ciblent des mélanges de populations posent un risque de surutilisation de stocks mineurs. Nous avons évalué la composition et l'exploitation des stocks de saumons atlantiques (Salmo salar) dans une pêche de subsistance sur la côte du Labrador (Canada) par l'analyse des mélanges génétiques et l'affectation d'individus a` la lumière de données microsatellitaires de référence (15 microsatellites, 11 829 individus, 12 groupes régionaux) couvrant l'aire de réparation de l'espèce dans la partie ouest de l'océan Atlantique. Les analyses bayésiennes et de maximum de vraisemblance de mélanges d'échantillons tirés de cette pêche sur une période de 6 ans (2006–2011, 1772 individus) indiquent que les stocks adjacents constituent de 96 % a` 97 % de cette pêche. Les estimations de l'exploitation associée a` cette pêche étaient les plus élevées pour le saumon du Labrador (de 4,2 % a` 10,6 % par année) et généralement <1 % pour le saumon d'autres régions. L'affection des individus des échantillons de la pêche indiquait que les contributions non locales a` cette pêche (p. ex. de Québec ou Terre-Neuve) étaient rares et principalement limitées au sud du Labrador, ce qui concorde avec les voies de migration passant par le détroit de Belle-Isle. L'étude illustre comment l'analyse génétique de pêches au saumon atlantique de stocks mélangés dans le nord-ouest de l'Atlantique a` la lumière de la nouvelle base de données de référence peut permettre de discriminer l'exploitation des différents stocks et révéler des comportements migratoires complexes. [Traduit par la Rédaction]