Genetic data from: Cryptic persistence and loss of local endemism in Lake Constance charr subject to anthropogenic disturbance

Habitat restoration can help to protect and support endangered species. Following the restoration of Lake Constance to oligotrophic conditions, deep-water charr (originally described as Salvelinus profundus Schillinger, 1901) were rediscovered after more than 40 years of presumed extinction caused by eutrophication. Subsequent targeted surveys lead to the capture of a further 127 deep-water charr and 233 sympatric normal charr, Salvelinus cf. umbla. Given a history of intensive stocking in the lake and the possibility of introgressive hybridization, a discussion arose about the genetic status and future conservation strategies of both forms. The current study gathered life history traits and morphological and population genomic data for both extant forms, for comparison with 60–120 years' worth of historical data and museum specimens. The extant deep-water charr resembled historical specimens in terms of body shape, but significant differences between historical and extant normal charr included a decline in gill raker number over time and distinctly different body shapes and growth patterns. RAD-based population genomic analyses of the contemporary samples support these results, revealing the two extant forms to be highly divergent, albeit with a few putative hybrids. SNPs-based population assignment tests of historical and contemporary samples strongly suggest that deep-water charr persisted unaltered in Lake Constance during the eutrophic phase. Meanwhile, none of the historical genomic samples could be assigned to the extant normal S. cf. umbla population. Functional analyses of gill raker number and stocking intensity pointed to stocking with non-endemic charr as the most likely reason for the disappearance of the endemic normal form. These results show that interplay between different anthropogenic impacts, i.e. eutrophication and stocking can lead to irreversible but hard-to-detect impacts on endemic biodiversity. Understanding these impacts is a prerequisite for effective conservation of endangered populations of cryptic fish.