Publication Abstract

The catadromous European eel Anguilla anguilla is critically endangered, yet substantial knowledge gaps remain on aspects of their complex lifecycle. Integral to understanding their emigration as silver eels back to spawning areas in the southern Atlantic Ocean is generating knowledge on their initial movements out of fresh waters and in-shore areas. Here, acoustic biotelemetry tracked the downstream migration of 25 silver eels in the River Test, southern England, and then their initial movements in the marine environment. One eel was never detected in the riverine or marine environment. Twenty-four eels were detected migrating downstream, with 19 tracked into the tidal area. The presence of in-river barriers did not inhibit their downstream movements. Thirteen eels out of 19 were detected in the marine environment and while two moved eastwards (one became resident within a harbour environment), the remainder all moved westwards and generally moved outside of the receiver array within 25 days, a linear distance of approximately 80 km. While eels were generally detected moving in the river in darkness, detections at sea were across the 24 h cycle, with detection depths up to 50 m. These movement data indicate these eels generally moved quickly out of the river and most then moved in the direction of their spawning area.

Sibusisiwe Moyo, J. Robert Britton, Thomas Major, Rosalind Wright, Andy Moore*, Mark Ives* and Tea Bašić*