Genetic Population Structure among Source Populations for Coaster Brook Trout in Nipigon Bay, Lake Superior

Abstract

AbstractPopulations of coaster brook trout Salvelinus fontinalis, a potadromous ecotype endemic to Lake Superior, have declined precipitously over the past 150 years. This study quantified the relatedness and genetic structure of remnant coaster and river‐resident brook trout within Nipigon Bay using microsatellite DNA markers. Individual assignment tests confirmed that coaster brook trout are a life history variant of brook trout derived from populations in tributary habitats, rather than a genetically distinct subspecies or evolutionarily significant unit. Furthermore, coasters appear to act as vectors for gene flow among riverine populations, providing genetic connectivity among allopatric tributaries. Molecular data indicated substantial gene flow among several below‐barrier populations, whereas other tributaries contained separate, largely discrete populations. Isolated above‐barrier populations showed the greatest interpopulation differentiation, with limited downstream gene flow observed within tributaries. The relative contributions of the sampled tributary populations to the coasters in Nipigon Bay were highly variable among rivers, indicating that management of source river populations will be critical for the effective conservation and restoration of coaster brook trout within Lake Superior.