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Contribution to the World Congress of Herpetology in Vancuver (August'11) by Gonzalo Mucientes, Nuno Queiroz, Nicholas Humphries & David Sims.
"The shortfin mako shark (Isurus oxyrinchus) is a highly migratory, pelagic species with circum-global distribution in tropical and temperate seas. This shark is commonly found in the Atlantic Ocean and are taken as bycatch in longlining and gillnetting operations for tuna and swordfish (Xiphias gladius), activities that have expanded rapidly during the last 20 years. High demand for fins and its good-quality meat mean makos are now highly prized by fishers. But despite the high prevalence, economic importance, and vulnerability of this species, little is known about its population dynamics and habitat-use. There is some evidence from conventional tagging and fishery studies that complex population structuring and movements may be contributing to recorded declines in the western Atlantic Ocean. Shortfin mako sharks may remain faithful to particular regions, which together with males and females apparently segregating into different regions for at least part of the year may result in differential exploitation of vulnerable components of the population (e.g. mature females, juveniles) exacerbating declines. The aim of this study is to elucidate for the first time the movements and behaviour of shortfin mako sharks from satellitelinked electronic tagging and relate this to remotely sensed environmental fields to identify fine-scale habitat preferences in the Atlantic Ocean. Pop-up archival transmitting (PAT) tags were deployed, recording vertical and horizontal movements and temperature preferences of mako sharks tagged in oceanic waters. satellite tags were programmed to detach 30, 60, 90, 120 or 180 days after deployment.
A total of 16 makos (8 males, 8 females) were caught and tagged in North Atlantic waters, specifically, in northwest, southwest and east of the Azores islands from 2009 – 2011. Tagged sharks ranged from 120 – 255 cm (fork length). Mako sharks displayed different movement and residency patterns, including a trans-Atlantic migration into western Iberia waters. Satellite tracked sharks also displayed deep diving behaviour into cold water, with maximum recorded depths of 1064 m (5.8 ºC) with temperature preferences ranging from 5.8 and 27ºC."
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