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.

全球范围内的渔业资源管理者广泛采用人工增殖放流手段，以维持休闲垂钓与商业捕捞共同利用的鱼类种群，但此类手段的效益仍存在争议。早期放流实践多使用外来种群，而当前的增殖项目则更多考虑对本地鱼类进行人工繁育（支持性增殖，supportive breeding）。解析此类管理策略所带来的复杂遗传效应，是一项兼具经济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如此。
本研究聚焦于日内瓦湖（横跨瑞士与法国）的衰退北极红点鲑（Arctic charr, Salvelinus alpinus）种群——该种群最初于20世纪80年代初期通过投放异地鱼类开展增殖放流，随后转为采用支持性增殖模式。基于此背景，本研究利用当代与历史样本开展遗传学调查，以刻画过去50年间，即人工孵化放流实施前后，该种群遗传多样性与遗传结构的演化历程。
研究结果显示，外源鱼类的引入与20世纪80至90年代的遗传瓶颈、哈迪-温伯格平衡（Hardy-Weinberg Equilibrium, HWE）的打破、遗传多样性的下降、产卵场间遗传分化程度的加剧，以及种群遗传组成的改变存在关联。结合环境条件的改善，后续三十年间采用本地鱼类开展的支持性增殖，使得种群重新恢复了哈迪-温伯格平衡与初始的遗传变异水平。但当前的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已出现显著的遗传均质化现象。
本研究在全面的时空框架下，阐明了不同增殖放流策略所带来的剧烈遗传效应，并表明通过非本地鱼类放流引发的遗传改变，可借助支持性增殖得到部分逆转。研究建议，基于保护的增殖项目应优先考虑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均质化进程。