Restricted movement range of European eels (Anguilla anguilla L.) in an oceanic island stream.

Research on the critically endangered European eel (Anguilla anguilla L.) has long been focused on the continental part of the species' wide distribution. Comparatively, we know very little about its ecology in the small stream habitats of the oceanic Macaronesian islands and whether it differs from that of continental estuaries, rivers and lakes. We used acoustic telemetry to investigate the movements of 36 yellow-staged eels for 1 year at a typical Azorean stream, with small pools below waterfalls interchanged by riffles and runs. Tagged eels had a restricted movement range and mostly stayed in a given pool. Such limited movements render this part of the population particularly susceptible to changes in the stream, which can seasonally run dry at some parts. These findings likely reflect the extreme habitat limitation in Azorean streams, and possibly an evolutionary adaptation to ensure growth under limited food supply and high competitive pressure. These specificities should be taken into account in future management plans for the European eel and its Azorean habitats.