Abstract
Large-scale hatchery releases are carried out for many marine fish species worldwide; nevertheless, the long-term effects of this practice on the genetic structure of natural populations remains unclear. The lack of knowledge is especially evident when independent stock enhancement programs are conducted simultaneously on the same species at different geographical locations, as occurs with red sea bream (Pagrus major, Temminck et Schlegel) in Japan. In this study, we examined the putative effects of intensive offspring releases on the genetic structure of red sea bream populations along the Japanese archipelago by genotyping 848 fish at fifteen microsatellite loci. Our results suggests weak but consistent patterns of genetic divergence (F ST = 0.002, p < 0.001). Red sea bream in Japan appeared spatially structured with several patches of distinct allelic composition, which corresponded to areas receiving an important influx of fish of hatchery origin, either released intentionally or from unintentional escapees from aquaculture operations. In addition to impacts upon local populations inhabiting semi-enclosed embayments, large-scale releases (either intentionally or from unintentional escapes) appeared also to have perturbed genetic structure in open areas. Hence, results of the present study suggest that independent large-scale marine stock enhancement programs conducted simultaneously on one species at different geographical locations may compromise native genetic structure and lead to patchy patterns in population genetic structure.
Highlights
Spatial patterns in genetic structure of organisms in the wild reflect historical and contemporary effects of micro-evolutionary processesPLOS ONE | DOI:10.1371/journal.pone.0125743 May 20, 2015Effects of Releases on the Genetic Structure of Red Sea Bream
While most studies have addressed the genetic effects of juvenile releases for specific programs at specific locations, little is known about the genetic integrity of large marine populations when several independent stock enhancement programs are conducted on the same species at different locations across its distribution range [11]
In addition to characterizing the genetic resources of the species in the country, we investigated whether independent largescale stock enhancement programs conducted simultaneously on the same species at different geographical locations may perturb the genetic structure of red sea bream in Japan; and if so, whether the effects are restricted to semi-enclosed areas or whether could they be detected in more open areas
Summary
Spatial patterns in genetic structure of organisms in the wild reflect historical and contemporary effects of micro-evolutionary processes (e.g., genetic drift, gene flow, mutation, selection). These strategies can contribute to increase recaptures; they can render small local native populations more vulnerable than in the open sea, where dispersal and gene flow possibilities are higher In this regard, while most studies have addressed the genetic effects of juvenile releases for specific programs at specific locations, little is known about the genetic integrity of large marine populations when several independent stock enhancement programs are conducted on the same species at different locations across its distribution range [11]. Genetic studies of the effects of stock enhancement mostly have been conducted in two prefectures, Kagoshima and Kanagawa In both cases, significant differences among the gene pools of released offspring and native wild populations were reported [23,24,25]. The northwestern prefecture of Akita appears as an exception, accounting for 500,000–1 million juvenile releases annually
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