| Abstract |
Amphihaline migratory fish are facing alarming declines due to anthropogenic and environmental pressures. In this context, environmental DNA (eDNA) emerges as a promising non-invasive approach to complement traditional population monitoring methods. We developed and validated species-specific genetic markers that enable the unambiquous detection and identification of five iconic migratory fish species (brown trout, Atlantic salmon, sea lamprey, European eel, and Alosa spp.). The aim was to assess whether the eDNA detected in water could reliably reflect the abundances measured at river counting stations. The results show effective detection for certain species and contexts but with significant variability depending on the markers and environmental conditions (temperature, turbidity, flow). For example, in the Adour River, peaks in eDNA concentrations were observed a few weeks after the migration peaks of trout and Alosa spp. Water temperature appears to play a major role in the release and persistence of eDNA, with optimal eDNA concentrations obtained at intermediate temperature ranges (around 18°C). In contrast, flow variations, especially in spring, seem to reduce species detectability due to eDNA dilution. This study represents an important step in integrating eDNA as a complementary tool to traditional monitoring methods for amphihaline migratory fish, particularly for species that are poorly documented at the national level. However, the complexity of the transport and degradation processes of DNA in aquatic environnements - still only partially understood - and the significant variability between river systems, call for continued research over several years to optimize sampling and analysis protocols, and to accurately integrate environmental parameters into reliable predictive models. |