Many species of marine mammals were drastically reduced (i.e., population bottleneck), and several nearly exterminated, by commercial hunters in the 19th and early 20th Centuries and there is evidence that the genetic variability in these populations and species was also substantially diminished (i.e., genetic bottleneck). Population genetics theory predicts that low genetic variability may compromise a populations’ or species’ persistence by making it less able to adapt to environmental changes or to reemerging or new diseases. Yet a number of species that have gone through severe population and genetic bottlenecks have recovered and are now robust and thriving. HSWRI scientists, working with collaborators from several institutions are investigating this paradox and continuing to investigate whether limited genetic variability presents long term challenges to their persistence. We are also using molecular genetic techniques to understand how local, regional, and distant populations of various species interact and how knowledge of the frequency and magnitude of these interactions can guide national and international management and conservation plans.