New boundaries: Redefining the geographical range of a threatened fish through environmental DNA survey

Accurate data on the distribution and population status of threatened fish species are fundamental for effective conservation planning and management. In this work, in order to reassess the distribution of the globally threatened Evia barbel, Barbus euboicus, we undertook an environmental DNA (eDNA) survey coupled with conventional electrofishing, focusing on major river basins in Evia Island in proximity to its known occurrence in a single Evian basin (Manikiatiko stream). For comparison purposes, we conducted eDNA sampling in several locations in the geographically closest continental river basin, the Sperchios basin (Central Greece) which hosts the closely related Barbus sperchiensis. Our results expand the known range of the Evia barbel on Evia adding four new river basins, apart from its type locality (Manikiatiko stream (EV3)). In a single Evian River, where the species had never been located before, there was also a positive eDNA signal for Barbus sperchiensis within the same basin. The research confirms the occurrence of Evia barbel in a wider geographical area, highlighting however the sensitive conservation status of the species due to its still very narrow geographical distribution. The biogeographical implications of our study, as well as potential conservation interventions, are discussed.