Assessing population genetic structure and hatchery introgression in eastern brook trout (salvelinus fontinalis) in the Beebe River Watershed

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brook trout , Beebe River (N.H.)
Lamy, Jared B.
In northern New England, stream fragmentation is most pervasive in the form of culverts at road crossings, a result of decades of logging. The Beebe River watershed (Campton/Sandwich, NH) is an example of a system that has been impacted by historical land use practices. Access to ten kilometers of headwater habitat was blocked by four undersized culverts, preventing Eastern Brook Trout (Salvelinus fontinalis) from accessing valuable spawning habitat and thermal refugia, as well as isolating populations above crossings. In September of 2017, an extensive restoration project replaced the culverts with stringer bridges, reconnecting streams that had been fragmented for decades. This restoration presented a unique opportunity to examine Brook Trout population genetic structure before and after restoration to develop an understanding of the success of the project in terms of its benefits to the persistence of Brook Trout. Prior to restoration in 2016, fin-clips (n=309) were collected via backpack electrofishing from throughout the watershed and genotyped at twelve microsatellite loci. Assignment analysis suggests populations above culverts belong to distinct genetic clusters. In contrast, results from non-fragmented tributaries suggest admixture is occurring where individuals are physically able to move throughout the watershed. Analysis of genotypes collected in 2018 (n=250) suggests minimal change in population structure post-restoration. Because the Beebe River watershed is heavily stocked with hatchery raised Brook Trout, the degree to which introgression of hatchery genetics into wild populations occurs is also being examined. Results suggest significant introgression has occurred throughout the study area.