Evaluation of genetic effects on wild salmon populations from stock enhancement

Atlantic salmon populations have declined in recent decades. Many of the threats to the species during its freshwater and coastal residency periods are known, and management approaches are available to mitigate them. The global scale of climate change and altered ocean ecosystems make these threats more difficult to address. Managers need to be aware that promoting strong, healthy, and resilient wild populations migrating from rivers is the optimal approach currently to reduce the impacts of changing ecosystems and low marine survival. We argue that a fundamental strategy should be to ensure that the highest number of wild smolts in the best condition leave from rivers and coastal areas to the ocean. There is great scope for water quality, river regulation, migration barriers, and physical river habitat improvements. Maintenance of genetic integrity and diversity of wild populations by eliminating interbreeding with escaped farmed salmon, eliminating poorly planned stocking, and reducing impacts that reduce population sizes to dangerously low levels will support the ability of Atlantic salmon to adapt to changing environments. Reducing the impacts from aquaculture and other human activities in coastal areas can greatly increase marine survival in affected areas. As most of the threats to wild salmon are the result of human activities, a focus on human dimensions and improved communication, from scientific and management perspectives, needs to be increasingly emphasized. When political and social will are coupled with adequate resources, managers often have the tools to mitigate many of the threats to wild salmon.

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“…and ensuring that all hatchery-produced fish are traceable so that the effects of stocking can be evaluated Hagen et al, 2019;Hagen et al, 2020).…”

Section: Artificial Stocking Of Natural Populations To Augment Abundancementioning

confidence: 99%

Atlantic salmon in a rapidly changing environment—Facing the challenges of reduced marine survival and climate change

Thorstad

Bliss

Breau

et al. 2021

Aquatic Conservation

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“…In the past few decades, stock enhancement has been one of the popular approaches for biodiversity conservation and fisheries management, particularly for species showing sharp declines in biomass. However, previous studies have shown that the ecological and genetic effects of hatchery releases are also of real concern because of potential negative impacts on wild populations as well as their adaptivity to varying degrees (Grant et al, 2017) [e.g., Atlantic salmon (Hagen et al, 2020), Salvelinus fontinalis (Marie et al, 2010), A. schlegelii (Shan et al, 2020)]. Although large yellow croaker has become one of the marine fish species cultured at the largest scale for hatchery release in mainland China, our results revealed no significant divergence or population structure among the JSW, ZSW, MZW, MYW, and YXW populations, while the SSBW population showed high genetic relatedness to the cultured population in terms of genetic structure and genetic diversity (Table 1, Figure 3, and Supplementary Figure 5).…”

Section: Is the Phylogeographical Pattern Of The Wild Large Yellow Croaker Population Influenced By Release Activities?mentioning

confidence: 99%

“…To recover the wild resources of large yellow croaker, large amounts of hatchery-reared juveniles have been released into the coastal waters of Fujian, Zhejiang, and Jiangsu provinces each year since 2000 (Liu, 2013). A series of previous studies have shown that stock enhancement usually has negative ecological and genetic impacts on wild populations (Grant et al, 2017;Hagen et al, 2020), such as genetic homogenization (Marie et al, 2010) and decreased genetic diversity (Shan et al, 2020). Moreover, hatchery-reared individuals may replace rather than increase the abundance of wild populations or may be harmful to other species through ecological interactions (Grant et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Resource Status and Effect of Long-Term Stock Enhancement of Large Yellow Croaker in China

Yuan

Lin

et al. 2021

Front. Mar. Sci.

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The large yellow croaker, Larimichthys crocea, was once the most abundant and economically important marine fish in China. Thus far, it has also been the most successful mariculture fish species in China. However, its wild stock severely declined in the 1970s because of overexploitation, and therefore hatchery release has been carried out for stock enhancement since 2000. As a migratory fish, large yellow croaker was divided into three geographical stocks according to ambiguous morphological and biological characteristics in early documents. To investigate the identity of wild large yellow croaker populations and assess the influence of hatchery supplementation on wild populations, a total of 2,785 cultured individuals and 591 wild individuals were collected from 91 hatcheries and six wild populations along the coast of mainland China and analyzed using two mitochondrial genes [cytochrome oxidase I (COI) and cytochrome b (Cyt b)] and one nuclear gene (RyR3). The higher haplotype diversity and moderate nucleotide diversity of wild large yellow croaker indicated that overexploitation, which caused a sharp decrease in biomass, did not lead to a loss of genetic diversity. According to phylogenetic construction and network analysis, the absence of a significant population structure pattern revealed a single panmictic population of wild large yellow croaker with exception of a population collected from the Sansha Bay, which showed high genetic relatedness to the cultured population, suggesting significant genetic effects resulting from stock enhancement. Overall, our study suggests no genetic differentiation in the entire wild population of large yellow croaker, which means that we have great flexibility in mixing and matching farmed and wild populations. However, since the result showed that domestication, the relaxation of purifying selection, increased genetic loads, and maladapted farmed fish will be at a selective disadvantage when cultured juveniles are released in the wild, the effectiveness of stock enhancement and the negative impact of hatchery-wild fish hybridization on the wild population must be carefully evaluated in future.

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“…Thus, long-term stock enhancement, using hatchery stocks, may cause a depletion of genetic diversity in local populations through direct replacement or genetic drift (Christie et al, 2012). Finally, restoration of wild populations with stock enhancement can reduce the Ne of the entire mixed population, based on the Ryman-Laikre effect (Hagen et al, 2021). But in this study, the S. schlegelii population had large Ne values before and after release and the confidence intervals were infinite (Pcrit = 0.05 or 0.02).…”

Section: Assessment Of the Potential Genetic Impactmentioning

confidence: 99%

Genetic Stock Identification and Adaptability of Hatchery-Reared Black Rockfish, Sebastes schlegelii, Released Into the North Yellow Sea waters

Liu

Wang

et al. 2022

Front. Mar. Sci.

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Successful stock enhancement refers to the maintenance of economic profit, whilst minimizing negative genetic and ecological effects. As hatchery environments differ from natural habitats, post-release identification of hatchery-reared juveniles, and estimation of their adaptability are essential steps in conducting responsible stock enhancement. The black rockfish is an important fishery species in Japan, South Korea and China. Overfishing has dramatically decreased natural resources and a stock enhancement program was first initiated in the Liaodong peninsula in 2019. We traced this program and used nine microsatellite markers to identify 279 individuals as being hatchery-reared, out of 710 captured fish, with a resource contribution rate of 39.30%. These results indicated that stock enhancement of this species is likely to maintain a positive economic performance. To understand the potential genetic impacts on the local wild population, the genetic patterns of S. schlegelii stocks (wild controls from 2017, wild controls from 2018, female broodstock from 2019, recaptured hatchery-reared fish from 2019 and recaptured non-hatchery-reared fish from 2019 stocks) from the same habitat were evaluated before and after artificial stocking. We found that the S. schlegelii population was able to maintain high genetic diversity and showed weak genetic differentiation, but potential genetic introgression derived from stock enhancement should be concerned. The hatchery-reared individuals showed good adaptability, as shown by feeding condition and growth status. There was no obvious morphology difference between hatchery-reared fish and their wild counterparts, but hatchery-reared fish seemed to be bigger in size (significantly higher in MDB and BW), had a larger head (significantly larger in PRL/HL and ID/HL) and smaller paired fins (significantly smaller PCFL/BL), when compared with wild individuals across all investigation months. Our results provided insights into management of black rockfish enhancement in the future.

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Evaluation of genetic effects on wild salmon populations from stock enhancement

Cited by 30 publications

References 47 publications

Atlantic salmon in a rapidly changing environment—Facing the challenges of reduced marine survival and climate change

Atlantic salmon in a rapidly changing environment—Facing the challenges of reduced marine survival and climate change

Resource Status and Effect of Long-Term Stock Enhancement of Large Yellow Croaker in China

Genetic Stock Identification and Adaptability of Hatchery-Reared Black Rockfish, Sebastes schlegelii, Released Into the North Yellow Sea waters

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