MITOCHONDRIAL-DNA ANALYSIS OF HARBOR PORPOISE, PHOCOENA-PHOCOENA, SUBPOPULATIONS IN NORTH-AMERICAN WATERS

Harbour porpoises, Phocoena phocoena, suffer heavy incidental exploita tion by commercial fisheries of North America. For effective managemen t of this problem, information on population structure is essential. M itochondrial DNA (mtDNA) of 204 harbour porpoises from North American waters was analysed primarily to assess population structuring and gen etic diversity. Nine restriction enzymes were used to survey a mean of 588 base pairs (or 3.6%) of the estimated size of harbour porpoise mt DNA (16 346 +/- 524 (SD) base pairs). Analysis of the frequency distri bution of haplotypes supports the classification of some previously pr oposed subpopulations within the western North Atlantic and suggests t hat females are more philopatric than males. High diversity estimates suggest that the western North Atlantic subpopulations are not serious ly depleted of genetic variation. The present study also showed that e astern North Pacific and western North Atlantic populations are fixed for haplotypes of different lineages with an estimated mean divergence of 2.3%. Under the reported rates of mtDNA evolution of 0.5-2.0%/mill ion years, the magnitude of this divergence estimate is inconsistent w ith the hypothesis that divergence of eastern North Pacific and wester n North Atlantic harbour porpoises dates only to the Pleistocene. Rece nt suggestions for separate Atlantic and Pacific subspecies are also s upported.