Mitochondrial DNA analysis of harbour porpoises (Phocoena phocoena) in the Baltic Sea, the Kattegat–Skagerrak Seas and off the west coast of Norway

Abstract

Incidental mortality of harbour porpoises, Phocoena phocoena, from captures in fishing gear has been documented consistently as severe in some European waters. Since fishing effort varies greatly among regions, management units must be defined for more effective conservation of this species. In this study, analysis of mitochondrial DNA (mtDNA) restriction fragments was performed to investigate the population structure of harbour porpoises in the Baltic Sea, the joint Kattegat–Skagerrak Seas and off the west coast of Norway. Mitochondrial DNA of 65 harbour porpoises collected from three regions was analysed with nine restriction enzymes. Analysis of the heterogeneity in the frequency distribution of haplotypes among provisional subpopulations revealed significant differences, which supports the recognition of three different subpopulations and thus three separate management units. Furthermore, indices of haplotypic diversity (range: 0.211 to 0.628) and nucleotide diversity (range: 0.070 to 0.168) of these provisional subpopulations were much lower than for western North Atlantic subpopulations, which is consistent with the view that harbour porpoises in European waters, particularly in the Baltic Sea, are depleted.