Population structure and seasonal movements of narwhals, Monodon monoceros, determined from mtDNA analysis.

We determined the nucleotide sequence of the first 287 base pairs in the mitochondrial control region from 74 narwhals, Monodon monoceros, collected in the North-west Atlantic. We detected four polymorphic sites that defined five haplotypes, two of which were found in single specimens. The same DNA sequence was characterized in an additional 353 specimens by digestion with two restriction endonucleases. In this manner each specimen could be assigned to one of the three most common haplotypes. The nucleotide diversity for the total sample (as well as the sequenced subset) was estimated as 0.0017 and pairwise genetic distances between haplotypes ranged from 0.0035-0.0070. The low nucleotide diversity and the low average pairwise genetic distance between haplotypes suggest a recent expansion in abundance from a small founding population. Despite the low degree of variation, frequencies of the common haplotypes differed markedly between areas. The results indicate isolation, even between geographically close areas, as well as fidelity to specific summer and autumn feeding grounds. Heterogeneity within a presumed single breeding ground suggests mixing of pods with different haplotypic composition.