Circumpolar genetic population structure of capelin Mallotus villosus

Capelin Mallotus villosus is the most abundant pelagic fish species in boreal and subarctic waters. The ecological and commercial importance of capelin emphasizes the need for a better understanding of the genetic population structure of the species and the mechanisms underlying its population dynamics. With this aim, 1155 capelin from the entire distributional range of the species were genotyped using 9 recently-developed microsatellite markers. The genetic analyses clearly demonstrated that the circumpolar capelin population can be divided into 4 regional groups: (1) West Pacific, (2) East Pacific, (3) Newfoundland, and (4) Northeast Atlantic and West Greenland. Highly significant genetic differentiation was observed between capelin from the western and eastern Pacific, and a high assignment success within both regions indicated minimal gene flow between these populations. Within the Atlantic Ocean, the Newfoundland population was differentiated from all the other samples. Among the remaining samples within the Atlantic Ocean the microsatellite data were less conclusive. Comparison of our results with studies of species with similar distribution, duration of planktonic stages and dispersal capacity suggests that genetic structuring of capelin within the complex system of the Northeast Atlantic Ocean cannot be ruled out.