Assessing the long-term genetic impact of historical stocking events on contemporary populations of Atlantic salmon (Salmo salar L.) (original) (raw)
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Fisheries Management and Ecology, 2008
Supplementation of wild fish with non-native or domesticated fish is common practice. However, these stocked and native fish differ both ecologically and genetically and, in the wild, they interact in a multitude of ways, often with negative repercussions for the native population. This study assessed the long-term genetic impact of historical stocking activities on a contemporary population of Atlantic salmon, Salmo salar L. During the 1960s salmon from hatcheries in Scotland and Iceland were transplanted to the River Dart, England. Microsatellite loci were used to assess the current level of population admixture between samples taken from the source location of the stocked fish during the 1960s and contemporary Dart populations. After allowances were made for natural genetic relationships between donor and recipient populations, the long-term impact of the historical stocking events on a catchment scale appears minimal. However, one tributary consistently reflected closer genetic relationships with the donor populations, indicating a possible long-term impact on a localised scale.
Ecology and evolution, 2013
While the stocking of captive-bred fish has been occurring for decades and has had substantial immediate genetic and evolutionary impacts on wild populations, its long-term consequences have only been weakly investigated. Here, we conducted a spatiotemporal analysis of 1428 Atlantic salmon sampled from 1965 to 2006 in 25 populations throughout France to investigate the influence of stocking on the neutral genetic structure in wild Atlantic salmon (Salmo salar) populations. On the basis of the analysis of 11 microsatellite loci, we found that the overall genetic structure among populations dramatically decreased over the period studied. Admixture rates among populations were highly variable, ranging from a nearly undetectable contribution from donor stocks to total replacement of the native gene pool, suggesting extremely variable impacts of stocking. Depending on population, admixture rates either increased, remained stable, or decreased in samples collected between 1998 and 2006 compared to samples from 1965 to 1987, suggesting either rising, long-lasting or short-term impacts of stocking. We discuss the potential mechanisms contributing to this variability, including the reduced fitness of stocked fish and persistence of wild locally adapted individuals.
Freshwater Biology, 2009
1. An important goal of conservation biology is to preserve the evolutionary potential of a species by maintaining natural levels of genetic diversity. Here, we assess the population differentiation in the Atlantic salmon, Salmo salar, listed in Annex II of the European Habitats Directive, to provide valuable information for its conservation in Normandy (France).2. Samples collected from 10 natural sites revealed that 13 of 14 microsatellite loci were polymorphic. Significant differentiation among populations was detected (FST = 0.054, P < 0.001), and all FST pairwise comparisons except one were significant. A genetic split was observed between populations inhabiting streams with limestone geology compared to those inhabiting streams with siliceous geology, which could reflect adaptative differences.3. Hatchery stocks used for the restocking of two rivers were genetically distinct from native stocks.4. Analysis of three stream habitats restored in 1995 showed that all were recolonized naturally by wild salmon from geographically close populations and no founder effects were detected. Allelic richness was similar between recolonized and wild populations.5. From a management perspective, our study revealed that restoration of habitat is very effective to recreate new populations in rivers from which salmon have disappeared and that natural recolonization can be fast and effective in terms of genetic diversity.
Endangered Species Research, 2020
Many Atlantic salmon Salmo salar populations in Europe are threatened by previous stocking with foreign hatchery strains. Temporal patterns of genetic characteristics of salmon from northern Spain, the southernmost European populations, were compared before and after species decline and heavy stocking with specimens from northern Europe. Eleven microsatellite loci were analysed in archival (scales from 1958-1960) and contemporary (2007-2008) samples from the River Sella. Temporal analyses revealed a similar heterozygosity between archival and contemporary samples, despite a drastic decrease in population abundance, while the contemporary sample showed a higher allelic richness due to the occurrence of foreign alleles. Considering only the alleles with at least 4% frequency in the archival sample, 2 alleles exclusive to the River Sella were absent in the contemporary sample, and 14 alleles showed a decrease of at least 4% frequency. Four alleles common in Scotland showed a high occur...
Conservation Genetics, 2013
Although the tendency of Atlantic salmon Salmo salar to form differentiated populations among rivers and among tributaries within large river systems ([100 km-long) is well documented, much less is known about population structure within small river systems (\30 km-long). In the present study, we investigated the genetic effects of straying of hatchery-reared salmon on population structure and genetic composition within the Ellidaár river system, a small system (21 km total length) in SW Iceland. We analyzed spatial and temporal variation of wild and domesticated samples (farmed and ranched; n = 931) using seven microsatellite loci. Estimates of population differentiation [F ST , genetic tree (D A )] and Bayesian cluster analysis (STRUCTURE) revealed a significant population structure as well as relative long-term temporal stability of the genetic composition in the main river from 1948 to 2005. However, the genetic composition of the tributary populations was unstable and genetically homogenized in recent years. Wild-hatchery hybrids were detected during the influx of strays as well as few years after, suggesting that introgression has changed the genetic composition of the wild populations. More investigations are needed in Iceland and elsewhere on possible fine-scale population differentiation and factors leading to it. Finescale population differentiation as observed in the present study has implications for the resolution with which harvest and habitat management of salmon should be conducted. In addition, farming and ranching operations should be located to minimize potential negative effects of strays on wild fish.
Loss of regional population structure in Atlantic salmon, Salmo salar L., following stocking
Ices Journal of Marine Science, 2006
Many wild Atlantic salmon populations have been stocked with cultured fish during the past century. To evaluate the degree and the direction of the resulting genetic changes in wild southern European populations of Atlantic salmon, the variation at microsatellite loci was examined in historical and modern scale samples from five Spanish and two French rivers. Significant genetic differentiation between neighbouring rivers, which is typical of Atlantic salmon and which existed before stocking, appears to have been lost after only a decade of stocking with fish of foreign origin. Apparent introgression of foreign-origin genes into local gene pools was detected in the populations studied. These results indicate that stocking risks the loss of genetic diversity in wild salmon populations.
ICES Journal of Marine Science, 2006
The Connecticut River lost its Atlantic salmon population as a result of human activity 200 years ago. Cultured stocks, derived mainly from the Penobscot River, were employed to restore the population, and an annual run of salmon has been successfully re-established, although the population is not yet self-sustaining. We examined variation at microsatellite loci in historical scale and modern tissue samples to evaluate the degree and direction of any genetic changes that have occurred in the introduced population. The current genetic pattern of the Connecticut River population is very similar to that of its Penobscot River donor population. We found no differences in heterozygosity, mean number of alleles per locus, number of migrants, or FST values between the two populations, suggesting that no genetic bottlenecks had occurred during the restoration programme.
Fisheries Management and Ecology, 2011
Population genetic studies can be useful for informing conservation and management. In Atlantic salmon, Salmo salar L., population structuring frequently occurs between river systems, but contrasting patterns occur within rivers, highlighting the need for catchment-specific studies to inform management. Here, population structure of Atlantic salmon was examined in the River Tamar, United Kingdom, using 12 microsatellite loci. Gene diversity and allelic richness ranged from 0.80 to 0.84 and from 8.96 to 10.24, respectively. Some evidence of genetic structure was found, including significant genetic differentiation between samples in different subcatchments (pairwise h and tests of genic differentiation), results from assignment tests and a pattern of isolation by distance. Conversely, STRUCTURE revealed only one population cluster, and an analysis of molecular variance showed no significant variation between subcatchments. Evidence of population bottlenecks depended on the mutation model assumed and is discussed with reference to catchment-specific studies of stock abundance. Implications for implementing management actions are considered.
The Use of Microsatellite DNA Loci for Genetic Monitoring of Atlantic Salmon Populations
North American Journal of Aquaculture, 2000
This work addresses the application of a new group of molecular markers, microsatellite loci, to monitor genetic diversity in stocks used in fish enhancement programs. To illustrate the potential use of these markers, we examined the genetic variation associated with the Connecticut River and Penobscot River populations of Atlantic salmon Salmo salar in the United States. Both rivers are stocked annually with fry from captive or cultured stocks that are one generation removed from sea-run adults. We analyzed microsatellite loci variation among sea-run adults and the derived cultured stock for the Connecticut River in a given year, along with two consecutive cohorts of cultured age-0 juveniles for the Penobscot River. Our results reveal subtle differences in allele frequencies between the two samples for each stock and some potential increases of homozygotes. These results demonstrate the potential value of microsatellite loci for routine genetic monitoring of cultured Atlantic salmon populations associated with restoration programs in the eastern United States.
While introductions and supplementations using non-native and potentially domesticated individuals may have dramatic evolutionary effects on wild populations, few studies documented the evolution of genetic diversity and life-history traits in supplemented populations. Here, we investigated yearto-year changes from 1989 to 2009 in genetic admixture at 15 microsatellite loci and in phenotypic traits in an Atlantic salmon (Salmo salar) population stocked during the first decade of this period with two genetically and phenotypically distinct source populations. We detected a pattern of temporally increasing introgressive hybridization between the stocked population and both source populations. The proportion of fish returning to the river after a single winter at sea (versus several ones) was higher in fish assigned to the main source population than in local individuals. Moreover, during the first decade of the study, both single-sea-winter and multi-sea-winter (MSW) fish assigned to the main source population were smaller than local fish. During the second decade of the study, MSW fish defined as hybrids were lighter and smaller than fish from parental populations, suggesting outbreeding depression. Overall, this study suggests that supplementation with nonlocal individuals may alter not only the genetic diversity of wild populations but also life-history traits of adaptive significance.