Metapopulation theory assumes a balance between local decays/extinctions and local growth/new colonisations. Here we investigate whether recent population declines across part of the UK harbour seal range represent normal metapopulation dynamics or are indicative of perturbations potentially threatening the metapopulation viability, using 20 years of population trends, location tracking data ( n = 380), and UK-wide, multi-generational population genetic data ( n = 269). First, we use microsatellite data to show that two genetic groups...