Across rather than between river genetic structure in Atlantic salmon Salmo salar in north‐east Scotland, UK: potential causes and management implications

Abstract

The aim of this study was to examine the genetic structuring, based on c. 4300 single nucleotide polymorphic markers, of juvenile Atlantic salmon Salmo salar sampled from 11 rivers in north-east Scotland, which form part of a radial drainage system. Within this area, sites in the upper mountainous and lower coastal sections of the different rivers were more closely related than sites from the upper and lower sections of the same river. Differentiation between fish from upper and lower sections was related to both distance from the sea and elevation, which were themselves correlated. The occurrence of such cross-river genetic grouping appears to be the result of both similar selective pressures resulting in homologous adaptive differences within each river and also recent common ancestry between rivers. Examination of historical tagging information showed high rates (27·4%) of between-river straying in this region that may help to maintain the across rather than between-river structure. The existence of cross-river groupings highlights the complex structuring of S. salar populations and may confound genetic identification of single-river stocks. Furthermore, the results presented show that cross-river structuring should also be an important consideration in managing S. salar stocks.

A large wild salmon stock shows genetic and life history differentiation within, but not between, rivers

“…This is however within typical Atlantic salmon straying rates between watersheds, estimated from other studies (3-10%, Stabell 1984;Jonsson et al 2003;Keefer and Caudill 2014). Cauwelier et al (2018b) examined 11 Atlantic salmon rivers in Scotland and observed a similar pattern of upstream-downstream rather than among-river genetic structuring, associated with exceptionally high rates of straying between rivers (27.4%). This suggests an alternative hypothesis that factors independent of the bifurcation are maintaining the parallel upstream-downstream structure in the Kalix and Tornio.…”

Evidence for contemporary and historical gene flow between guppy populations in different watersheds, with a test for associations with adaptive traits

“…In our case, cross-watershed gene flow was found in two areas, both closely adjacent tributaries at the same elevation. This finding is reminiscent of a recent study of Atlantic salmon (Salmo salar), where fish located at the same elevation but in different rivers were more related to each other than to fish in the same river but at a different elevation (Cauwelier, Stewart, Millar, Gilbey, & Middlemas, 2018). Uniquely in our study, the two cross-watershed genetic linkages seemed to have occurred on different timescales (historical and contemporary) in different parts of the watershedsneither of which are associated with any known human-mediated introductions.…”

The early marine distribution of Atlantic salmon in the North‐east Atlantic: A genetically informed stock‐specific synthesis

“…This will require new screening panels and data baselines to be developed, ideally encompassing adaptively relevant and life‐history markers (e.g. Cauwelier et al., 2018). Encompassing markers such as Vgll3, six6 , also offers the possibility of comparing ocean migration and distribution patterns for different sea age phenotypes (Aykanat et al., 2020; Ayllon et al., 2015; Barson et al., 2015), enhancing understanding stock‐specific responses to environmental change.…”