Replicate divergence between and within sounds in a marine fish: the copper rockfish (Sebastes caurinus)

Understanding the factors that influence larval dispersal and connectivity among marine populations is critical to the conservation and sustainable management of marine resources. We assessed genetic subdivision among ten populations of copper rockfish (Sebastes caurinus) representing paired samples of outer coast and the heads of inlets in five replicate sounds on the west coast of Vancouver Island, British Columbia, using 17 microsatellite DNA loci. Overall, subdivision (F-ST) was low (F-ST=0.031, P<0.001), but consistently higher between paired coast and head of inlet sites (mean F-ST=0.047, P<0.001) compared to among the five coast sites (mean F-ST=-0.001, P>0.5) or among the five head of inlet sites (mean F-ST=0.026, P<0.001). Heterozygosity, allelic richness and estimates of effective population size were also lower in head of inlet sites than in coast sites. Bayesian analysis identified two genetic groups across all samples, a single genetic group among only coast samples, two genetic groups among head of inlet samples and two genetic groups within each sound analysed separately. Head of inlet copper rockfish tended to be shorter with lower condition factors and grew more slowly than coast sites fish. Reduced physical connectivity and selection against immigrants in contrasting outer coast-head of inlet environments likely contribute to the evolution of population structure of copper rockfish. Based on genetic connectivity, coast sites appear to be better served by existing marine protected areas than are head of inlet sites.