Swedish Agency for Marine and Water Management

This report is aimed at reviewing current knowledge on the genetic population structure of harbour porpoise (Phocoena phocoena) in Swedish and adjacent waters (here defined to include the Baltic, Belt, Kattegat, and Skagerrak Seas). Population genetic information is necessary for effective conservation and management of the species, and one of the key questions refers to how many genetically distinct populations of porpoises that exist in this region.

The review was conducted within the framework of ongoing efforts of the Swedish Environmental Protection Agency to provide conservation and management guidelines for the harbour porpoise. No new data has been collected; the review is based exclusively on previously published information.

The harbour porpoise is regarded as threatened in most parts of its distribution range, which includes the three major geographic areas of the North Pacific Ocean, the North Atlantic, and the Black Sea/Sea of Azov. The global threat status of the species is "vulnerable". In Sweden, the abundance has declined during the second half of the 20th century, and the population reduction is considered particularly dramatic within the Baltic Sea, where the census size is estimated to only a few hundred individuals.

We collected previously published scientific studies that directly or indirectly address questions concerning the genetic population structure of the harbour porpoise through search of literature databases. We summarize and discuss the conclusions of those studies focusing on papers that are based on clear cut genetic data obtained by means of variousmolecular techniques. Several workers address the issue of population differentiation through studying characters for which the genetic basis is not fully understood (e.g., skullor tooth morphology, time for reproduction, etc.), and it is therefore not clear to what extent the variation of such characters reflect divergence on the gene level. Some of those studies are referred to in this report, but our discussion is based exclusively on the results of the "direct" genetic studies.

The report also includes background sections on harbour porpoise biology and population status, as well as basic information on biological diversity on the gene level (genetic diversity), processes that affects this diversity, and methods for studying population genetic variability patterns.