Winter migration and diving behaviour of porbeagle shark, Lamna nasus, in the Northeast Atlantic

Abstract

Abstract Saunders, R. A., Royer, F., and Clarke, M. W. 2011. Winter migration and diving behaviour of porbeagle shark, Lamna nasus, in the Northeast Atlantic. – ICES Journal of Marine Science, 68: 166–174. The porbeagle is one of the top marine predators in the North Atlantic. However, little is known about its biology, abundance, or spatial ecology there. Results are presented on the migration and behaviour of three porbeagles tagged with archival pop-up tags off Ireland between September 2008 and January 2009. One shark migrated >2400 km to the northwest of Morocco, residing around the Bay of Biscay for approximately 30 days. The other two remained more localized in off-shelf regions around the Celtic Sea/Bay of Biscay and off western Ireland. The sharks occupied a broad vertical depth range (0–700 m) and a relatively limited temperature range (∼9–17°C), with notable variations in diving behaviour between individual sharks. There were distinct day–night differences in depth distribution, each shark being positioned higher in the water column by night than by day. Night-time depth distribution also appeared to be driven by the lunar cycle during broad-scale migration through oceanic waters. Our results show that porbeagles occupy and traverse regions of high fishing activity where they are potentially vulnerable to population depletion. Such large-scale movement outside the ICES Area underlines the need for international coordination in their assessment and management.