Environmental DNA analysis indicates that migration barriers are decreasing the occurrence of European eel (Anguilla anguilla) in distance from the sea

Abstract

The European eel (Anguilla L.) is considered critically endangered by the IUCN Red List, and recruitment remains low. One of the challenges for the species today is migration barriers that limit their habitat. Along the Norwegian coast, like in other countries, the abundance of eels appears to decrease with distance from the sea. This pattern may be a result of factors like water temperature, water quality, competition, and habitat suitability and availability. This study aims to use environmental DNA (eDNA) analysis to investigate the potential relationship between migration barriers and the decreasing occurrence of eels in distance from the sea by the coast of southern Norway. Sixty locations with potential migration barriers are investigated by collecting water samples upstream and downstream from each construction before eDNA from each sample is isolated and analyzed by real-time PCR with specific primers and probes matching A. anguilla. The results reveal that the probability of detecting eel eDNA decreases significantly with number of hydroelectric power stations and their associated basins, even when the effect of distance to sea is accounted for. In addition, there is a clear border at which eel eDNA could no longer be detected upstream of the major watercourses. Therefore, it is likely that the migration of eels is prohibited by these constructions, which seem to constitute a much greater challenge than every other type of potential migration barrier investigated in this study.

Keywords

• Environmental DNA
• Anguilla Anguilla
• Passage barriers
• Conservation
• Real-time PCR