Microsatellite DNA analysis of Pacific hake Merluccius productus population structure in the Salish Sea

This study presents the first microsatellite DNA study of population structure of Pacific hake, Merluccius productus (also known as Pacific whiting) within the Salish Sea, which has been identified as a distinct population segment under the US Endangered Species Act and is currently listed as a federal Species of Concern. In contrast, a separate coastal stock component of Pacific hake represents the most abundant commercial groundfish species on the US West Coast. We surveyed variation at 10 microsatellite DNA loci in a total of 655 individuals from three Salish Sea locations (Port Susan (PTS) and Dabob Bay in Washington and south-central Strait of Georgia (SOG) in British Columbia), three coastal locations (two off southern California and one in the Gulf of Alaska), and the Northern Gulf of California (GOC), México. No significant differences were detected among temporal samples from both PTS and SOG locations. Multilocus measures of population subdivision between coastal and Salish Sea populations (all pairwise FST ≥ 0.03) and between PTS and SOG populations (FST ≥ 0.01) suggest a moderate degree of demographic isolation among these spawning populations. No significant genetic differences were found among the three coastal Pacific hake samples; however, Pacific hake from the GOC were significantly differentiated from both coastal (FST > 0.05) and Salish Sea (FST ≥ 0.03) Pacific hake. Correlations between genetic and geographic distance showed that Pacific hake display a very strong isolation by distance signal, both over the whole study area (∼4500 km; r2 = 0.94) and within the Salish Sea (∼280 km; r2 = 0.72). This study suggests that PTS and SOG populations are to some extent demographically isolated from each other.