Loss of genetic integrity in wild lake trout populations following stocking: insights from an exhaustive study of 72 lakes from Québec, Canada

Abstract

Stocking represents the most important management tool worldwide to increase and sustain commercial and recreational fisheries in a context of overexploitation. Genetic impacts of this practice have been investigated in many studies, which examined population and individual admixture, but few have investigated determinants of these processes. Here, we addressed these questions from the genotyping at 19 microsatellite loci of 3341 adult lake trout (Salvelinus namaycush) from 72 unstocked and stocked lakes. Results showed an increase in genetic diversity and a twofold decrease in the extent of genetic differentiation among stocked populations when compared to unstocked. Stocked populations were characterized by significant admixture at both population and individual levels. Moreover, levels of admixture in stocked populations were strongly correlated with stocking intensity and a threshold value of total homogenization between source and stocked populations was identified. Our results also suggest that under certain scenarios, the genetic impacts of stocking could be of short duration. Overall, our study emphasizes the important alteration of the genetic integrity of stocked populations and the need to better understand determinants of admixture to optimize stocking strategies and to conserve the genetic integrity of wild populations.

Climate, Demography, and Zoogeography Predict Introgression Thresholds in Salmonid Hybrid Zones in Rocky Mountain Streams

“…Relaxation of introgression in native taxa has been observed following the cessation of stocking elsewhere e.g., between native Guadalupe bass Micropterus treculii and introduced smallmouth bass M . dolomieu [83] or native and introduced stocks of lake trout Salvelinus namaycush [84]. Likewise, suppression or removal of naturalized rainbow trout populations could reduce the likelihood of substantial introgression [85], as could epizootics to which rainbow trout are more susceptible (e.g., whirling disease, but see [86]).…”

Stocking activities for the Arctic charr in Lake Geneva: Genetic effects in space and time

“…Here, the three decades of supportive breeding, from 1983 onwards, allowed the partial restoration of the original genetic nature of Lake Geneva's population and its levels of diversity (lesser genetic differentiation between current and original fishes, and similar levels of H o , A r , and F is ). We show that the Arctic charr responded significantly, and very rapidly to these changes, possibly also due to the high intensity of stocking (which correlates to the amount of genetic changes; Valiquette et al, 2014), and the important contribution of stocked fishes in the population (45%-90% depending on age class ;Caudron et al, 2014). In some cases, genetic diversity was even found to increase following such restocking practices, when lake populations are highly structured spatially and may admix with releases obtained from breeders caught in close-by, yet On the other hand, the continuous restocking clearly led to the rapid and strong homogenization of the lake's population (toward null F st ): even if the original genetic structure was low to begin with, it is virtually inexistent nowadays.…”

“…The common practice is to raise and release the offspring of few adults (artificially obtained by in-farm fecundation), yielding a disproportionate amount of siblings among released stocks and thus low effective size and genetic diversity. Fishes from this period also seem substantially different than original wild stocks (disruptive clustering on the PCA, Figure (Miller, Mero, & Younk, 2012;Perrier, Guyomard, Bagliniere, & Evanno, 2011;Perrier et al, 2013), an effect intimately linked to stocking intensity (Valiquette et al, 2014). In addition, it is not excluded that demographic processes (i.e., historical decline, as reported during the 1970s in the lake) may have contributed to this genetic bottleneck.…”

“…The massive releases of Danish fishes (1979)(1980)(1981)(1982) caused significant changes in the genetic structure, nature, and diversity of the lake's population. This pattern likely reflects a situation where many fishes are the product of admixture between exotic and local fishes (as, e.g., Gharrett, Smoker, Reisenbichler, & Taylor, 1999;Le Cam et al, 2015;Valiquette, Perrier, Thibault, & Bernatchez, 2014), which may have induced outbreeding depression (breakdown of co-adapted interactions; Allendorf et al, 2001;Edmands, 2007;Bougas et al, 2010). The common practice is to raise and release the offspring of few adults (artificially obtained by in-farm fecundation), yielding a disproportionate amount of siblings among released stocks and thus low effective size and genetic diversity.…”

Recent genetic changes in enhanced populations of sea trout (Salmo truttam.trutta) in the southern Baltic rivers revealed with SNP analysis

“…Utter et al 1987;Wenne 1992;Poteaux and Berrebi 1997;Halvorson et al 2001;Was et al 2004;Poćwierz-Kotus et al 2007;Wenne et al 2007;Filipowicz et al 2008;Beaumont et al 2010;Wenne et al 2011;Kohout et al 2013;Nakajima et al 2014). Microsatellites are regularly used in fisheries related applications and research (Was and Wenne 1998;Griffiths et al 2013;Perrier et al 2013;Pukk et al 2013;Bernaś et al 2014;Koljonen et al 2014;Thaulow et al 2014;Valiquette et al 2014). However, the high potential of more recently discovered and developed single nucleotide polymorphisms (SNPs) to uncover population structures and find genomic regions (islands) under selection has become increasingly recognized (Lamaze et al 2012;Pustovrh et al 2012;Ozerov et al 2013;Milano et al, 2014;Poćwierz-Kotus et al 2015b;Sušnik Bajec et al 2015).…”