Genetic evidence for limited trans-Atlantic movements of the harbor porpoise Phocoena phocoena

In the North Atlantic, 14 regional subpopulations have been proposed for the harbor porpoise Phocoena phocoena (Linnaeus, 1758). To what degree these populations experience genetic interchange is relatively unknown, particularly on the larger scale of the North Atlantic as a whole. With the recent completion of several regional genetic studies on population structure of the harbor porpoise in the North Atlantic, came the opportunity to combine datasets in an effort to broaden the geographic scope of focus. Three datasets comprised of mitochondrial DNA control region sequences, representing the Northeast and Northwest Atlantic regions were pooled and reanalyzed to examine the degree of trans-Atlantic exchange among harbor porpoise populations, and to examine the evolutionary history of the species in the North Atlantic. The movement of harbor porpoises across the Atlantic appears to occur at a low level. Genetic variability in the Northeast Atlantic is significantly lower than in the Northwest Atlantic, and may indicate a more recent recolonization for the Northeast Atlantic. The star phylogeny of northeastern haplotypes, with a number of rare haplotypes closely related to the most abundant type, indicates a recent population expansion. A disjunction in haplotypic frequencies between the Northeast and Northwest Atlantic probably occurs east of Greenland, but the exact location and source of the disjunction has yet to be determined. Received: 23 March 1998 / Accepted: 3 December 1998