Genetic introgression between wild and stocked brown trout in the Douro River basin, Spain

Abstract

The genetic diversity of Spanish brown trout is currently threatened by stocking with exogenous brown trout from Central and Northern Europe. In the Douro River basin 25% of the analysed populations in the present study showed introgression by genes of hatchery origin. The mean introgression estimated by the single locus approach (S |) varied from 0 to 22% among populations, with a mean value of 3%. The hatchery allele markers were absent in populations where stocking ceased in 1993. However, the introgression effect was observed in all populations stocked until 1998. It seems that cessation of stocking is a good measure for restoring native populations. A thorough review of published and present data of genetic interactions between wild and stocked brown trout in Spanish rivers indicates different levels of introgression between basins. The absence of a clear geographical pattern in the introgression level suggests that ecological interactions and local stocking programmes may play an important role in stocking success. Finally, several guidelines are provided for conservation and management of native brown trout populations in Spanish rivers. 2001 The Fisheries Society of the British Isles

Genomewide introgressive hybridization patterns in wild Atlantic salmon influenced by inadvertent gene flow from hatchery releases

“…Except for five comparisons involving Loobu samples, introgression estimate (Taggart & Ferguson ; Almodovar et al . ) based on SNPs resulted in higher values compared to the alternative estimate I (Karlsson et al . ) based on admixture modelling and multilocus microsatellite genotype data.…”

“…Second, introgression was quantified from allele frequency shifts for each SNP marker based on the expression: = ( p w ‐ p n ) × ( p h ‐ p n ) −1 , where p w , p h and p n are the allele frequencies of the wild population, the hatchery stock and the native population sample collected before large‐scale releases, respectively (Taggart & Ferguson ; Almodovar et al . ). To ensure that the locus‐specific and genomewide introgression estimates were as accurate as possible, for subsequent analysis, we used only a subset of SNPs (upper 30th percentile) that showed the highest genetic differentiation ( F ST ) between hatchery stock and the earliest wild samples.…”

Interactive effects of cover and hydraulics on brown trout habitat selection patterns

“…Consequently, the knowledge of the habitat requirements of species is essential for assessing different impacts from human activities on fish communities. This is especially relevant in salmonid wild populations of south European countries which are currently threatened by habitat destruction, pollution, introduction of exotic especies, overfishing and introgression of foreign genes as a result of artificial stocking (Almodóvar and Nicola, 1998Almodóvar et al, 2001Almodóvar et al, , 2002Almodóvar et al, , 2006aElvira and Almodóvar, 2001).…”

Habitat Use by Native and Stocked Trout (Salmo Trutta L.) in Two Northeast Streams, Portugal

“…However, limitations in space and time associated with high effective costs have resulted many times in the low success rate of these activities. Furthermore, several studies have reported negative consequences of stocking such as the spread of parasites and diseases (MOFFIT et al, 1998), an increase of competitive interactions (NICKELSON et al, 1986;McMICHAEL and PEARSONS, 1997), and, more recently, genetic introgression (BLANCO et al, 1998;CAGIGAS et al, 1999;ALMODÓVAR et al, 2001). …”