Effective size of a wild salmonid population is greatly reduced by hatchery supplementation

Abstract

Many declining and commercially important populations are supplemented with captive-born individuals that are intentionally released into the wild. These supplementation programs often create large numbers of offspring from relatively few breeding adults, which can have substantial population-level effects. We examined the genetic effects of supplementation on a wild population of steelhead (Oncorhynchus mykiss) from the Hood River, Oregon, by matching 12 run-years of hatchery steelhead back to their broodstock parents. We show that the effective number of breeders producing the hatchery fish (broodstock parents; N b ) was quite small (harmonic mean N b ¼ 25 fish per brood-year vs 373 for wild fish), and was exacerbated by a high variance in broodstock reproductive success among individuals within years. The low N b caused hatchery fish to have decreased allelic richness, increased average relatedness, more loci in linkage disequilibrium and substantial levels of genetic drift in comparison with their wild-born counterparts. We also documented a substantial Ryman-Laikre effect whereby the additional hatchery fish doubled the total number of adult fish on the spawning grounds each year, but cut the effective population size of the total population (wild and hatchery fish combined) by nearly two-thirds. We further demonstrate that the Ryman-Laikre effect is most severe in this population when (1) 410% of fish allowed onto spawning grounds are from hatcheries and (2) the hatchery fish have high reproductive success in the wild. These results emphasize the trade-offs that arise when supplementation programs attempt to balance disparate goals (increasing production while maintaining genetic diversity and fitness).

Genetic effects of marine stock enhancement: a case study based on the highly piscivorous Japanese Spanish mackerel

“…In general, therefore, x should be larger than N c /(N c + N w ) in almost all hatchery-release programs, and this produces a Ryman-Laikre effect (N e < N w ). Christie et al (2012) found a substantial Ryman-Laikre effect for the steelhead population in the Hood River. In our example, N c /(N c + N w ) = 11/(11 + 433) = 0.0248 and x = 0.11, which satisfies the condition for a Ryman-Laikre effect of x > N c /(N c + N w ).…”

“…When information is available before the potential impact, the sampling design is often referred to as a before-after control-impact (BACI) design (Smith 2002). This type of design can be used to detect the genetic effects of hatchery release, although in practice these comparisons are not feasible for many populations because of the lengthy history of anthropogenic intervention (Christie et al 2012). We used mitochondrial DNA (mtDNA) and microsatellite DNA (msDNA) markers to evaluate the population structure of the JSM pre-and post-stocking, changes in genetic variation, and the genetic mixing proportions of hatchery fish in the SIS.…”

“…This is known as the Ryman-Laikre effect, by which the inbreeding effective size of the entire population (wild plus hatchery) is reduced relative to that of the original wild population (without hatchery release) (Ryman and Laikre 1991). Despite such a serious effect on stocked populations, the Ryman-Laikre effect has been largely ignored in current practice for over 20 years (Christie et al 2012). A second concern is the potential for a reduction in fitness of the stocked population.…”

Population genetic structure in European lobsters: implications for connectivity, diversity and hatchery stocking

“…areas closed to fishing; Hoskin et al 2011) is that the admixture of hatchery stock can compromise the fitness of wild populations: rearing in artificial environments can promote traits that are maladapted to the wild and may be introduced to natural stock (Araki et al 2007, Christie et al 2012a, while relative genetic homogeneity among cultured individuals may reduce the effective size of the targeted stock (Christie et al 2012b). Hatchery stocking also has the potential to disrupt the structuring of intra-specific genetic diversity (Ward 2006, Lorenzen et al 2010.…”

PERTUMBUHAN DAN VARIASI GENETIK IKAN BANDENG, Chanos chanos DARI PROVINSI ACEH, BALI, DAN GORONTALO, INDONESIA

“…Hal ini dikarenakan penurunan variasi genetik akan berdampak pada pertumbuhan, dan rentan terhadap serangan penyakit, serta perubahan lingkungan (Stringwell et al, 2014). Penurunan keragaman dapat terjadi menggunakan induk dalam jumlah yang terbatas dan berkerabat dekat akibat terjadinya peningkatan inbreeding yang berdampak performa (Christie et al, 2012;Fisch et al, 2015). Oleh karena itu, perlu dilakukan pengamatan variasi genetik dan pertumbuhan benih bandeng hingga menjadi calon induk dari lokasi yang berbeda.…”