Acknowledgements
We thank Þorvaldur Gunnlaugsson, Gísli Víkingsson (†), Yves Morin and Santiago Lens for providing access to Icelandic, Canadian and Iberian porpoise samples, respectively. We would further like to thank Katja Havenstein, Ljerka Lah, and all the other people in our lab that isolated DNA from porpoise samples throughout the years. Large-scale computations were carried out at the High-Performance Computing Cluster managed by ZIM (Zentrum für Informationstechnologie und Medienmanagement) at the University of Potsdam. We are grateful to the ZIM team for assisting with the installation of modules in the computing cluster. This work was financially supported by the Bundesamt für Naturschutz (FKZ 3521532214) granted to R.T. and the University of Potsdam