Doctoral Thesis - Aarhus Universitet (2011)


The population status of harbour porpoises has been of concern for several years due to anthropogenic influences, especially incidental bycatch in gillnet fisheries. Proper management of a wide-ranging species such as the harbour porpoise requires reliable information on distribution, migrations, status of biological populations, and habitat preferences. This PhD thesis examines these issues. Harbour porpoise distribution is examined by means of satellite tracking (Paper II) and acoustic surveys, along with the agreement in results between these two very different methods (Paper III). The data from satellite tracking are also used to identify the boundaries of a genetically distinct harbour porpoise population and new abundance estimates are calculated for this population (Paper IV). Next, the underlying causes governing harbour porpoise distribution are explored by reviewing available information on harbour porpoise diet (Paper V) and correlating the distribution of satellite tracked porpoises with distribution of a main prey species, herring (Paper VI). Finally, the seasonal variations in distribution of harbour porpoises observed in a Danish strait, the Sound, are explored by examining the stomach content of porpoises from the area. Overall, this PhD thesis introduces several new applications for satellite telemetry data that – in combination with acoustic surveys – has significantly contributed to the current knowledge of harbour porpoise distribution. Furthermore, the thesis provides evidence of a porpoise-prey relationship which is important information in the conservation of the species, due to its influence on harbour porpoise distribution.