Habitat use by loggerhead sea turtles Caretta caretta off the coast of eastern Spain results in a high vulnerability to
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ORIGINAL PAPER
Habitat use by loggerhead sea turtles Caretta caretta off the coast of eastern Spain results in a high vulnerability to neritic fishing gear Luis Cardona Æ Mo´nica Revelles Æ Mari Luz Parga Æ Jesu´s Toma´s Æ Alex Aguilar Æ Ferran Alegre Æ Antonio Raga Æ Xavier Ferrer
Received: 2 February 2009 / Accepted: 18 August 2009 / Published online: 16 September 2009 Ó Springer-Verlag 2009
Abstract Previous studies of loggerhead sea turtles have concluded that drifting longlines were the main threat for immature specimens in the western Mediterranean, because immature loggerhead sea turtles mainly inhabit oceanic waters. However, recent aerial surveys have revealed large numbers of immature loggerhead sea turtles over the continental shelf of eastern mainland Spain, where turtles are exposed to neritic fishing gears but not to drifting longlines. We satellite-tracked seven loggerhead sea turtles (minimum straight carapace length (SCLmin) range: 36.5– 55.0 cm) to assess whether the turtles in this region are vagrants from the adjoining oceanic regions or whether these loggerheads mostly inhabit the continental shelf. Satellite-tracking revealed that six of the tagged turtles avoided the oceanic realm and made extended use of the continental shelf, whereas only one individual could be considered a true vagrant as it avoided the continental shelf and primarily used the oceanic habitat. These results are in Communicated by U. Sommer. L. Cardona M. Revelles (&) A. Aguilar X. Ferrer Department of Animal Biology, Faculty of Biology, University of Barcelona, Avda. Diagonal 645, 08028 Barcelona, Spain e-mail: [email protected] M. L. Parga F. Alegre Marine Animal Rescue Center (CRAM), Camı´ Ral 239, 08330 Premia` de Mar, Spain Present Address: M. L. Parga Submon, C/Rabassa 49-51, local 1, 08024 Barcelona, Spain J. Toma´s A. Raga Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, PO box 22085, 46071 Valencia, Spain
sharp contrast with those previously reported for immature loggerhead sea turtles of similar size from the southwestern Mediterranean and fit well a relaxed ontogenic model that was recently proposed for loggerhead sea turtles in the central Mediterranean. Furthermore, these results demonstrate the vulnerability of loggerhead sea turtles of eastern mainland Spain to neritic fishing gears, as three of the seven turtles died and one was bycaught incidentally while being tracked over the continental shelf.
Introduction Bycatch in drifting longlines has often been considered to be the main threat for immature loggerhead sea turtles Caretta caretta (Linnaeus 1758) throughout the Mediterranean, as they experience high rates of bycatch in this fishery (Margaritoulis et al. 2003; Lewison et al. 2004). The highest rates of incidental bycatch are recorded in the south-western Mediterranean (Aguilar et al. 1995; Lewison et al. 2004; Deflorio et al. 2005; Camin˜as et al. 2006), probably because immature loggerhead sea turtles inhabiting that region ha
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