Abstract
The extent to which stray, hatchery-reared salmon affect wild populations is much debated. Although experiments show that artificial breeding and culture influence the genetics of hatchery salmon, little is known about the interaction between hatchery and wild salmon in a natural setting. Here, we estimated historical and contemporary genetic population structures of chum salmon (Oncorhynchus keta) in Prince William Sound (PWS), Alaska, with 135 single nucleotide polymorphism (SNP) markers. Historical population structure was inferred from the analysis of DNA from fish scales, which had been archived since the late 1960’s for several populations in PWS. Parallel analyses with microsatellites and a test based on Hardy-Weinberg proportions showed that about 50% of the fish-scale DNA was cross-contaminated with DNA from other fish. These samples were removed from the analysis. We used a novel application of the classical source-sink model to compare SNP allele frequencies in these archived fish-scales (1964–1982) with frequencies in contemporary samples (2008–2010) and found a temporal shift toward hatchery allele frequencies in some wild populations. Other populations showed markedly less introgression, despite moderate amounts of hatchery straying. The extent of introgression may reflect similarities in spawning time and life-history traits between hatchery and wild fish, or the degree that hybrids return to a natal spawning area. The source-sink model is a powerful means of detecting low levels of introgression over several generations.
Highlights
Interactions between hatchery-reared and wild Pacific salmon can be a source of genetic change within and among wild populations [1]
Even when the initial hatchery brood stock is drawn from nearby wild populations, hatchery culture can change the genetic makeup of the hatchery population, especially in segregated hatchery populations, in which brood stocks are selected from fish returning to the hatchery [2,3]
Some hatchery fish inevitably stray into wild populations, and the degree of influence these fish have on wild populations is related to the intensity of stock enhancements [4], the amount of genetic divergence between hatchery and wild populations [4,5], and the extent of genetic introgression of hatchery genotypes into wild populations [6]
Summary
Interactions between hatchery-reared and wild Pacific salmon can be a source of genetic change within and among wild populations [1]. A key variable moderating the effects of hatcheryreared strays on wild populations appears to be the degree of lifehistory divergence between the hatchery and wild populations [4,6,7]. The effects of stray hatchery fish on wild populations can be measured in several ways. While stray hatchery fish may influence wild populations ecologically [9], they may not necessarily mate with wild fish. Run timing in a wild population of coho salmon (Oncorhynchus kisutch) shifted to earlier times as a result of the genetic influence of strays from a hatchery in which eggs were taken from the early portion of the run [11]
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