Long‐term residence of juvenile loggerhead turtles to foraging grounds: a potential conservation hotspot in the Mediterranean

Abstract

1. Identifying highly frequented areas is a priority for sea turtle conservation. Although juveniles represent the bulk of the population, a minority of studies have investigated their movement patterns.2. Six large juvenile loggerhead turtles that were found and released in an important foraging ground in the Mediterranean, the Tunisian continental shelf were tracked. Tracking data were obtained via satellite for periods ranging from 120 to 225 days and allowed the identification of high use areas.3. All turtles generally performed apparently non-directed, wandering movements in waters with a wide range of seafloor depths. They showed clear residential behaviour to the region with no evident seasonal pattern. Core areas of residence were in the neritic zone or on the edge of the continental shelf, largely overlapping among individuals, and were much smaller than residential oceanic areas reported elsewhere.4. When integrated into current knowledge, these results suggest an ecological-behavioural model of a gradual shift from a pelagic-vagile to a benthic-sedentary life style with progressive reduction of home ranges. 5. They also highlight an area of the continental shelf and offshore waters as potential core foraging ground for large juvenile loggerhead turtles in the Mediterranean informing future spatial management for loggerhead turtles.

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…In general, resident areas of juveniles in oceanic zones are much wider than in neritic zones (Revelles et al 2007b;Cardona et al 2009;Casale et al 2012aCasale et al , 2012b (Figure 4), as also observed for adults in the Mediterranean and elsewhere (Hawkes et al 2006;Schofield et al 2010a). Long-term residence of juveniles in neritic foraging grounds seems more common than in oceanic areas and it has been observed in various locations through tag returns (Casale et al 2007a;Revelles et al 2008) and satellite tracking Cardona et al 2009;Hochscheid et al 2010;Casale et al 2012aCasale et al , 2012bHochscheid et al 2013) (Figure 3). The juvenile neritic foraging sites are, however, usually larger than the adult neritic sites, with juveniles showing a propensity to wander over quite large areas (e.g.…”

“…A degree of permanence in the same area was indicated by tag returns in the western and eastern Mediterranean (Casale et al 2007a), and was directly observed through satellite tracking in some cases in the western Mediterranean (Revelles et al 2007a) but not in others, either in the western (Cardona et al 2005;Eckert et al 2008;Cardona et al 2009) or in the eastern Mediterranean (Bentivegna 2002). In general, resident areas of juveniles in oceanic zones are much wider than in neritic zones (Revelles et al 2007b;Cardona et al 2009;Casale et al 2012aCasale et al , 2012b (Figure 4), as also observed for adults in the Mediterranean and elsewhere (Hawkes et al 2006;Schofield et al 2010a). Long-term residence of juveniles in neritic foraging grounds seems more common than in oceanic areas and it has been observed in various locations through tag returns (Casale et al 2007a;Revelles et al 2008) and satellite tracking Cardona et al 2009;Hochscheid et al 2010;Casale et al 2012aCasale et al , 2012bHochscheid et al 2013) (Figure 3).…”

“…Some just wandered across wide areas, with no sign of residence at any specific site (Bentivegna 2002;Casale et al 2007a;Eckert et al 2008;Cardona et al 2009;Hochscheid et al 2010) (Figure 3). Others frequented somewhat smaller areas (Cardona et al 2005;Revelles et al 2007aRevelles et al , 2007bEckert et al 2008;Cardona et al 2009;Hochscheid et al 2010;Casale et al 2012aCasale et al , 2012b (Figure 3), in some cases remaining for a long time in very restricted sites (Hochscheid et al 2010;Mencacci et al 2011). The areas frequented and the routes followed are the result of a combination of surface circulation patterns and the turtles' active swimming Revelles et al 2007b).…”

A critical review of the Mediterranean sea turtle rescue network: a web looking for a weaver

“…1). The Pelagie Islands, for example, are a core foraging ground here (Casale et al 2012b). Individuals from the key Mediterranean turtle rookeries, i.e., western Greece, Crete, and Cyprus, frequent these central Mediterranean feeding grounds (Margaritoulis et al 2003, Broderick et al 2007, Casale et al 2008a, Zbinden et al 2008.…”

“…The North African coast is apparently an important migratory pathway for loggerheads across the Mediterranean (Broderick et al 2007, Casale et al 2012b. Seasonal movements include southbound emigration movements from the northern Adriatic , Zbinden et al 2008, Zbinden et al 2011) and movements of juveniles in the western Mediterranean (Cardona et al 2009).…”