Population assignment and local adaptation along an isolation-by-distance gradient in Pacific cod (Gadus macrocephalus)

The discernment of populations as management units is a fundamental prerequisite for sustainable exploitation of species. A lack of clear stock boundaries complicates not only the identification of spatial management units, but also the assessment of mixed fisheries by population assignment and mixed stock analysis. Many marine species, such as Pacific cod, are characterized by isolation-by-distance, showing significant differentiation but no clear stock boundaries. Here, we used restriction-site associated DNA (RAD) sequencing to investigate population structure and assess power to genetically assign Pacific cod to putative populations of origin. Samples were collected across the species range in the Eastern Pacific Ocean, from the Salish Sea to the Aleutian Islands. A total of 6,425 putative biallelic single nucleotide polymorphisms were identified from 276 individuals. We found a strong isolation-by-distance signal along coastlines that mirrored previous microsatellite results, and p...