Publication Abstract

Repeated seasonal migration by a thornback ray in the southern North Sea

E. Hunter, A. A. Buckley, C. Stewart and J. D. Metcalfe

Previous analyses of the population structure of thornback rays, Raja clavata L., based on conventional tagging studies, have suggested local sub-populations, between which little exchange of individuals is thought to occur. This feature of the biology of thornback rays coupled with late maturation and low fecundity make these fish highly vulnerable to localised extinction due to fishery exploitation. Here we present an example of a thornback ray tagged with an electronic data storage tag in the Thames Estuary on 06/10/99, recaptured after 504 days at liberty 276 km NW on the western Dutch coast, having recorded 423 days of data. Its migration was reconstructed using the tidal location method, and illustrates seasonal migration out of the Thames Estuary to the Dutch coast during the autumn and winter feeding season, then a return to the Thames estuary during spring to spawn. This individual provides the first direct evidence of repeated seasonal migration outside of the area commonly thought of as the species home range. This observation has significant implications with regards the use of closure management for the conservation of this species.

Reference:

E. Hunter, A.A. Buckley, C. Stewart and J.D. Metcalfe, 2005. Repeated seasonal migration by a thornback ray in the southern North Sea. Journal of the Marine Biological Association of the UK, 85: 1199-1200.