Data from: Stocking activities for the Arctic charr in Lake Geneva: genetic effects in space and time

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 the present 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 of genetic diversity, an increase of 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 spatio-temporal framework, and suggests that genetic alteration by non-local 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.

全球渔业资源管理者广泛采用人工增殖放流手段，以维持休闲捕捞与商业捕捞所依赖的鱼类种群，但其实施效益始终存在争议。早期的放流实践多使用外来品系，而当前的增殖项目则更多采用本地鱼类开展人工繁育，即辅助繁育（supportive breeding）。阐明此类管理策略所引发的复杂遗传效应，是一项兼具经济价值与保护意义的重要研究课题，在鱼类种群衰退的背景下尤为关键。本研究聚焦瑞士与法国交界的日内瓦湖内正面临衰退的北极红点鲑（Salvelinus alpinus）种群——该种群最初于20世纪80年代初通过异地鱼类进行增殖放流，后续转而采用辅助繁育手段。基于此，本研究结合当代与历史样本开展遗传调查，以厘清人工繁育辅助措施实施前后近50年间该种群的遗传多样性与遗传结构演变历程。研究结果显示，异地鱼类的引入与20世纪80至90年代的遗传瓶颈、哈迪-温伯格平衡（Hardy-Weinberg Equilibrium, HWE）偏离、遗传多样性下降、产卵场间遗传分化加剧以及种群遗传组成改变密切相关。结合后续改善的栖息环境，长达三十年的本地鱼类辅助繁育工作，使该种群重新恢复了哈迪-温伯格平衡与初始遗传变异水平。但当前各产卵场尚未完全恢复其原始遗传组成，且全湖范围内的产卵场间已出现广泛的遗传同质化现象。本研究在全面的时空框架下，揭示了不同增殖放流策略所带来的剧烈遗传效应，并表明异地放流引发的遗传改变，可通过辅助繁育得到部分逆转。本研究建议，基于保护目标的增殖项目应优先考量本地种群的遗传多样性，并制定合理的操作规范，以限制该北极红点鲑种群的遗传同质化进程。