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

Abstract

Artificial stocking practices are widely used by resource managers worldwide, in order to sustain fish populations exploited by both recreational and commercial activities, but their benefits are controversial. Former practices involved exotic strains, although current programs rather consider artificial breeding of local fishes (supportive breeding). Understanding the complex genetic effects of these management strategies is an important challenge with economic and conservation implications, especially in the context of population declines. In this study, we focus on the declining Arctic charr (Salvelinus alpinus) population from Lake Geneva (Switzerland and France), which has initially been restocked with allochtonous fishes in the early eighties, followed by supportive breeding. In this context, we conducted a genetic survey to document the evolution of the genetic diversity and structure throughout the last 50 years, before and after the initiation of hatchery supplementation, using contemporary and historical samples. We show that the introduction of exotic fishes was associated with a genetic bottleneck in the 1980–1990s, a break of Hardy–Weinberg Equilibrium (HWE), a reduction in genetic diversity, an increase in genetic structure among spawning sites, and a change in their genetic composition. Together with better environmental conditions, three decades of subsequent supportive breeding using local fishes allowed to re‐establish HWE and the initial levels of genetic variation. However, current spawning sites have not fully recovered their original genetic composition and were extensively homogenized across the lake. Our study demonstrates the drastic genetic consequences of different restocking tactics in a comprehensive spatiotemporal framework and suggests that genetic alteration by nonlocal stocking may be partly reversible through supportive breeding. We recommend that conservation‐based programs consider local diversity and implement adequate protocols to limit the genetic homogenization of this Arctic charr population.

Howling from the past: historical phylogeography and diversity losses in European grey wolves

“…range retraction has triggered population differentiation in alpine chipmunks [49]). Analyses of historical DNA also evidenced reduction of diversity and/or shifts in genetic composition and structure among a wide array of other declining animals, including birds [50 -53], fishes [54] as well as insects [55,56]. In comparison to most of these regional studies however, our historical phylogeography has the advantage to analyse fine-scale genetic fluctuations using a large number of historical samples over an extended biogeographical region and constitutes one of the most exhaustive spatio-temporal survey of historical DNA to date.…”

Warming winters threaten peripheral Arctic charr populations of Europe

“…The resident charr populations are considered indigenous to each lake. Following drastic declines in the Arctic charr of Lakes Bourget and Geneva during the twentieth century, presumably due to eutrophication, large-scale restocking of the native populations with allochthonous eggs occurred in the early 1980s (Cachera et al 2010;Caudron et al 2014;Savary et al 2017). A single documented introduction into Bunaveela with an Icelandic strain of charr eggs occurred in 1971 (Piggins and Went 1971), although the population is most likely native-the population has been self-sustaining since at least the 1970s and Bunaveela shares many specific physical characteristics with other native Irish charr lakes (Igoe and Hammar 2004).…”

Genetic evaluation of migratory fish: Implications for conservation and stocking programs

“…Studies in which population genetics tools are used to investigate gene flow and to identify migrants among the fish population are needed (e.g., Almada et al, 2017). Moreover, assessment of the genetic diversity status of fish species downstream and upstream of hydropower dams to detect possible effects of the dams and extensive fish stocking is an important step for conservation (Cooper et al, 2017; Savary et al, 2017; Vera‐Escalona, Senthivasan, Habit, & Ruzzante, 2018). In Brazil, the Companhia de Desenvolvimento Vale São Francisco (Codevasf) has implemented fish stocking programs at the Três Marias (TM) hydrobiology and fish farming station since 1980, with the release of thousands of fish broods into the upper São Francisco River.…”