Satellite Tagging of Basking Sharks (Cetorhinus maximus) Reveals Potential Conservation Gaps in the Western North Atlantic Ocean

Highly mobile marine species present challenges to conservation because they often move across geopolitical boundaries.  The basking shark (Cetorhinus maximus) is a globally vulnerable species, and is currently protected through international conservation conventions and domestic regulations in some range states.  The species has an expansive range, but little is known of its large-scale movement patterns and the degree to which individuals make trans-boundary movements.  To help quantify trans-boundary movements in this species, we tagged 57 basking sharks with pop-up satellite archival tags (PSATs) in their summer/fall foraging grounds off Massachusetts between 2004 and 2011.  Reconstructed tracks revealed extensive offshore movements, with some individuals traveling over 7,000 km from the tagging location.  Significant time was spent in International Waters and within the Exclusive Economic Zones (EEZs) of nations where they are not legally protected.  Tagging also identified movements of some sharks to the EEZs of nations not previously considered within their range.  Although vulnerability to fisheries may be comparatively low outside the United States EEZ, potential impacts of bycatch and other extractive marine activities should be assessed within these unprotected regions.  The regular international travels of basking sharks in the western North Atlantic may necessitate expanded international coordination in conservation efforts.