The first ‘lost year’ of Mediterranean sea turtles: dispersal patterns indicate subregional management units for conservation

Abstract

Identifying highly frequented areas is a priority for sea turtle conservation, and the distribution of young individuals in open waters represents a major knowledge gap due to methodological biases. The drift of hatchlings from 38 loggerhead Caretta caretta and 10 green Chelonia mydas turtle nesting sites in the Mediterranean was simulated for the first 6 mo of life, with simulations repeated for 5 different years (2001 through 2005). Results indicate that hatchlings from the Levantine and south-central Mediterranean sites are mainly retained in the same areas of origin, while those from the Ionian area mainly disperse to the Ionian, Adriatic and southcentral Mediterranean areas. Combining hatchling dispersal with existing empirical information on juveniles and adults, a general distribution model among nesting sites, and oceanic and neritic foraging grounds for Mediterranean sea turtles is proposed. The Levantine zone may be particularly key for the conservation of the Mediterranean populations of both species, since it may host the highest concentration of individuals. Subregional management units identified by dispersal patterns may facilitate turtle conservation through a relatively small-scale international approach. In-water studies in specific zones are identified as a research priority for improving current knowledge and informing conservation plans. KEY WORDS: Caretta caretta · Chelonia mydas · Loggerhead turtle · Green turtle · Dispersal · Conservation · Mediterranean Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 498: [263][264][265][266][267][268][269][270][271][272][273][274] 2014 turtle species could potentially inform conservation plans for their respective Mediterranean populations (e.g. Schofield et al. 2013).The loggerhead turtle is the most abundant sea turtle species in the Mediterranean, and reproduces mainly in Greece, Turkey, Cyprus and Libya (Casale & Margaritoulis 2010). Loggerhead turtles frequent the entire marine area of the Mediterranean, with high occurrences reported in the oceanic zones of (1) the westernmost part of the basin (from the Alboran Sea to the Balearic Islands), where most individuals are of Atlantic origin (Carreras et al. 2006), (2) the Strait of Sicily, and (3) the Ionian Sea. Loggerheads are also found in high abundance in the neritic zones in the north Adriatic, off Tunisia-Libya, off Egypt, and off the southeast coast of Turkey (Casale & Margaritoulis 2010). Green turtles primarily reproduce on nesting beaches in Turkey, Cyprus and Syria (Casale & Margaritoulis 2010). They primarily occupy neritic areas in the easternmost part of the basin, in addition to foraging areas in Greece and Libya (Casale & Margaritoulis 2010).Current knowledge on the distribution of sea turtles in the Mediterranean waters is based on data from strandings (Tomás et al. 2008, Türkozan et al. 2013, incidental catch in fishing gear (reviewed by Casale 2011), tag returns (Margaritoulis et al. 2003, Casale et al. 2007b, Revelles et...

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

“…As with loggerheads, information on the distribution of small turtles is particularly deficient, but in green turtles this applies to larger juveniles as well, given that no tracking experiment has been ever undertaken. Hatchling dispersal simulations indicated that green turtle hatchlings are mainly retained in the Levantine basin, where the nesting sites are (Casale & Mariani 2014). A high proportion of green turtles smaller than 30 cm CCL was reported to occur in southern Turkey waters ) while low numbers of small turtles < 40 cm CCL frequent the Adriatic (Lazar et al 2004), especially in the southern part, the Ionian and even the Tyrrhenian seas around Italy (Bentivegna et al 2011).…”

“…extension of shallow areas offering suitable neritic foraging sites is in the northern Adriatic and the Libyan/Tunisian shelf, these represent key areas for both Mediterranean green and loggerhead turtles, given that both areas are frequented by adults and juveniles. Other factors may, however, play a role in determining the movement patterns observed: for instance, recent evidence suggests that the foraging locations of adult turtles might be influenced by their drift scenarios as hatchlings Scott et al in press), and this would explain, for example, why few adults forage in the western part of Mediterranean, given that rookeries are confined to the Eastern basin (see also Casale & Mariani 2014). Mediterranean adult loggerheads do, however, exhibit some variety in their movements, with some turtles foraging in offshore oceanic waters for at least part of their inter-reproductive phase, sometimes keeping on the move without fixing to any specific site (Zbinden et al 2008;Luschi et al 2013;Schofield et al 2013).…”

“…In the Mediterranean, recent simulations of hatchling dispersal have indicated that hatchlings from the Levantine and central nesting sites are mainly retained in the same areas of origin, while those from the Ionian region disperse widely to the Ionian, Adriatic and south-central Mediterranean areas Casale & Mariani 2014).…”

“…The loggerhead turtle is the most common species in the Mediterranean Sea, where it nests mainly in the eastern part, from which juveniles then disperse widely throughout the basin (Margaritoulis et al 2003;Casale & Margaritoulis 2010;Hays et al 2010a;Casale & Mariani 2014). The Mediterranean loggerhead population shows a genetic divergence from the Atlantic populations (Bowen & Karl 2007), and a population substructure (Laurent et al 1998;Carreras et al 2007;Clusa et al 2013), indicating the presence of independent management units for conservation.…”

Active dispersal in loggerhead sea turtles ( Caretta caretta ) during the ‘lost years’

“…The trajectories of passively drifting particles are compared with those of observed turtles released from the same date and nesting location in the western North Pacific, thereby testing the passive migration hypothesis for juvenile loggerhead sea turtles in the North Pacific Ocean. Such insights will help assess the role of long-distance transport from currents and provide useful long-term information on small juveniles during a period where little is known [40]. This knowledge can also provide critical geographical information for conservation management strategies in areas that may host high concentrations of young individuals from this population.…”