Harp Seals comprise three populations associated with whelping areas on pack ice in the Greenland Sea, White Sea, and Northwest Atlantic “Gulf” and “Front”. Complete mitochondrial DNA genome sequences have identified nearly 600 single-nucleotide polymorphisms ("SNPs"). Every individual has a unique mtDNA sequence. The figure shows evidence for the existence of deep ancestral clades confined to the eastern populations, and relatively close relationships within and between western populations in a more recent clade. The occurence of individuals taken in the Greenland Sea (green squares at left) within this "western" genotype clade suggests historical movement from west to east.