Recolonisation or invasion? First insights into the origin of the newly established beaver populations in Bulgaria using eDNA

After a series of reintroductions (including unofficial releases) and natural recolonisations during the last decades, the Eurasian beaver (Castor fiber) is returning throughout Europe. However, it is hard to distinguish the species from its American relative, Castor canadensis, which has also been successfully introduced and is thriving in some parts of the continent as an invasive species. In this context, obtaining genetic information for the newly recorded populations is important for taking appropriate management actions. The current paper presents the results of the first genetic assay of five recently established beaver populations along the River Danube and two of its tributaries in Northern Bulgaria. The non-invasive method of eDNA sampling was applied. We found that all populations belong to C. fiber and are of the haplotypes from the refugial populations in Norway and France. We hypothesise that they naturally spread from Romania, where reintroductions have been done using individuals from Bavaria, who were, in turn, translocated from Scandinavia, France, Russia, and Poland.