THE POPULATION-STRUCTURE OF THE HARBOR PORPOISE, PHOCOENA-PHOCOENA, IN DANISH WATERS AND PART OF THE NORTH-ATLANTIC

A study of the homogeneity between putative stocks of Phocoena phocoen a in the North Sea and inner Danish waters was performed using isozyme electrophoresis. Two polymorphic systems, mannose phosphate isomerase (MPI) and phosphoglucomutase (PGM) were used in the analysis. A two-l ocus homogeneity test showed an effect of season and locality on the g enotypic distribution. This led to a division of the total sample into season and into the two localities, the inner Danish waters (IDW) and the North Sea. The samples were then compared to the Hardy-Weinberg e xpectations where a deficit in heterozygotes was observed in the North Sea sample in both systems and at the Pgm locus in the total sample, indicating a mixing of sub-populations. A hierarchical contingency tab le analysis, also based on the genotypic distribution, showed a combin ed effect of season and locality and only an insignificant effect of s ampling period, thus supporting the division into season and locality. The seasonal effect is further supported by earlier observations of a seasonal migration of harbour porpoises out of the Baltic in winter. A significant difference was observed between the two supposed sub-pop ulations, IDW-summer and North Sea-summer samples, based on the genoty pic distribution. This could also be a reflection of the sample sizes. On the basis of samples obtained from Canada, West Greenland and Holl and a preliminary study of the population structure on a larger scale, comprising the North East and North West Atlantic, was performed. The results so far accord well with the hitherto accepted sub-populations of P. phocoena in the North Atlantic.