Genetic Structuring of Brook Trout Populations in the Connecticut River Basin

Brook trout (Salvelinus fontinalis) are the only native trout in streams of the Connecticut River basin and the eastern US.  Within this range, brook trout persistence is threatened by many factors including increasing stream temperatures, competition with non-native fish species, stream network fragmentation from dams and roads, and habitat degradation through poor land management of riparian zones, sedimentation from road runoff, and land development in watersheds resulting in reduced water quality.  In many watersheds, these threats have forced brook trout out of larger streams and limited them to headwater habitats.  While many attempts to restore brook trout populations are underway, many populations are still well below historic abundances.  The objective of this study is to determine the spatial scale of genetic structuring of brook trout in the Connecticut River basin and characterize factors that influence its variation.  Sampling occurred within the watersheds of two main tributaries to the Connecticut River, the Westfield River, MA and the West River, VT.  We obtained genetic samples from three sub-watersheds within these larger watersheds.  Within a sub-watershed, genetic samples were taken from four or five tributaries and the sub-watershed mainstem.  We analyzed brook trout genetic samples at eight microsatellite loci.  These loci were used to assess how genetic diversity and genetic divergence varied across the hierarchy of spatial scales that were sampled.  In most sub-watersheds, the majority of genetic diversity appears to occur within streams of a sub-watershed.  In some sub-watersheds, there was significant genetic divergence among sample sections within streams and among streams within sub-watershed.  However, there is also genetic evidence indicating that gene flow between streams within sub-watersheds does occur.  The use of population genetic analyses has allowed us to determine that conservation efforts should focus on the sub-watershed scale.  Management efforts that help promote gene flow both within and among streams should improve genetic diversity and population persistence. A more thorough understanding of what influences variation in the spatial scale of population structuring is key to making effective conservation and management decisions for this species.