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Satellite tracking studies of sea turtles in the Mediterranean began with Hays et al. (1991) in which one loggerhead, Caretta caretta, individual was tracked during her internesting period. With the development of more sophisticated satellite tags, both loggerheads and green turtles have been tracked (Godley et al. 2002; Bentivegna 2002; Cardona et al. 2005). In the eastern Mediterranean, satellite tracking studies involving green turtles, Chelonia mydas, were carried out in areas such as Cyprus, Syria and Turkey and results show that green sea turtles nesting in the Mediterranean use Turkish,

Libyan, Egyptian, and Tunisian coasts as foraging grounds (Godley et al. 2003; Broderick et al. 2007, Rees et al. 2008). In this paper we report the findings of our post-nesting tracking study of two adult female green turtles tagged during the 2007 and 2008 breeding seasons. The main goal of this study was to determine the post- nesting migration routes and the foraging grounds of green turtles nesting at Akyatan Beach, Province Adana, Turkey.

Platform terminal transmitters (Kiwisat PTT 101, Sirtrack, New Zealand) were used to track turtle movements. The tags were 190 x 62 x 35 mm, 430 g and powered by two C battery cells, making them capable of transmitting data for 260 days with a one day on and one day off duty schedule. The PTTs were attached to the second vertebral scutes, which were first sanded smooth and cleaned with acetone to eliminate any organic material. A two-part epoxy glue (Bison Epoxy Brand) was used for the attachments. Tagged individuals were selected from females encountered while nesting on the beach in July (Table 1). The tagging process was not started until after oviposition ended.

Turtle positions were determined using the Argos system (CLS, France). Location classes 3, 2, 1, 0, A and B reflect the accuracy of the location with 3 being the most accurate and B being the least accurate. The accuracy of classes 3, 2, and 1 are <150 m, <350 m and <1000 m, respectively. Classes 0, A and B have no upper limits of location accuracy. Locations 3, 2, 1, 0 and relevant results from classes A and B were used to evaluate turtle migration routes following nesting.

Table 1.. Total number of turtle locations and their accuracy classes for two tracked green turtles from Akyatan Beach, Turkey (d=days).

A total of 189 (Turtle 007) and 269 (Turtle 008) locations were received during the tracking processes (Table 1). Of these 111 (Turtle 7) and 135 (Turtle 8) locations were useful for reconstructing the migration route (Table 1). Coordinates with location classes of 1, 2, and 3 were primarily used to construct the migration routes. We discarded 0 and Z locations due to inherent errors, and included A and B class locations when they appeared appropriate.

Figure 1. The migration routes of Turtles 7 (dotted line) and 8 (solid line). The triangle shows the release site at the nesting beaches and the solid circles represent the tracking endpoints.

After depositing her last nest on 01 August, one day after the deployment of the tag, Turtle 7 immediately left the nesting area. After travelling 2740 km over 75 days, she reached the Gulf of Sidra, Libya, following the coastlines of Northern Cyprus and Egypt (Fig. 1). She migrated directly to the south until she reached the open sea between Turkey and Cyprus, then she turned southwest along the northern shores of the Karpaz Peninsula, Cyprus. This was the first open sea stage following nesting. Arriving at the Karpaz Peninsula, Turtle 7 followed the coastline of northern and eastern Cyprus. She turned south again for 171 hours and travelled 417 km in the open sea until she arrived at the shores of Alexandria, Egypt. She stayed in the coastal waters of Egypt and Libya during her path westward until she arrived at her foraging grounds around the Gulf of Sidra, Libya (Fig. 1), where she stayed for 95 days until the last transmission.

Turtle 8 started to move in a westward direction immediately after her nesting season ended and 12 days and 351 km of coastal migration later, she reached her foraging grounds at the coastal areas between Manavgat-Alanya, Turkey.

Table 2. A statistical summary of open sea and coastal movements during migration of green turtles nesting in Turkey.

Throughout its migration, Turtle 7 used both coastal areas and the open sea and her activity varied within these habitats. She swam faster in the open sea (mean = 2.27 km/hr; max = 4.1 km/hr; min = 0.96 km/hr) than when she was close to shore (mean= 1.46 km/ hr; max= 3.1; min= 0.90). The area between Cyprus and Egypt, which was the longest open sea pathway in her migration route was traversed quicker (speed = 2.44 km/hr) than the coastal pathways in both Cyprus (speed = 1.57 km/hr) and North Africa (speed = 1.47 km/hr) (Table 2).

Our results are similar to the findings of Godley et al. (2002), Broderick et al. (2007) and Rees et al. (2008). Those studies reported that many of the green turtles nesting in Turkey, Cyprus and Syria followed a route from the southeast Cyprus to the Egyptian coasts and mostly chose foraging habitats along Tunisian and Libyan shores where food is available, including the seagrasses Posidonia oceanica and Zostera spp. in both lagoon and coastal waters (Short et al. 2007). The data from bycatch trawl fisheries have shown that the eastern Mediterranean waters of Turkey (Oruç 2001) and the coastal waters of Egypt (Venizelos & Nada 2000) are important foraging areas for green sea turtles. Northern Africa also has warmer waters compared to the northern parts of the Mediterranean; these are generally selected as overwintering areas for Caretta caretta and Chelonia mydas species nesting in both Turkey and Cyprus.

Table 3. Comparison of speed data between different studies on green sea turtles in the east Mediterranean.

The results of both open sea and coastal speed data show similarity to those presented by Godley et al. (2002), Godley et al. (2003) and Rees et al. (2008) (Table 3).

Whereas sea turtles hatchlings and juveniles appear to follow dominant water currents, the interactions between oceanic currents and adults remain uncertain due to active movements of adult sea turtles in their environment. Turtle 7 did not follow surface currents of the eastern Mediterranean in coastal waters and generally actively swam through eddies in the open sea. Nichols et al. (2000), Godley et al. (2003) and Bentivegna et al. (2007) all emphasized that adult sea turtles make characteristic and independent straight-line movements between their foraging and nesting areas without using currents.

When the Mediterranean surface current maps and the migration route of turtle 7 were overlapped, it was determined that turtle 7 follows a counter-current route to the foraging area along the North African coast. This kind of movement requires more energy to swim. Contrary to this, when the migration pattern of turtle 7 is reversed, the negative impact of the current is eliminated hence less energy is used to migrate back to the nesting grounds. Thus, this female would use less energy for her reproductive migration than for her post-nesting migration, which may be a beneficial strategy as suggested by Luschi et al. (2003). In contrast, turtle 8 moved with the currents to her foraging area. The shorter distance travelled by turtle 8 may mean reduced energetic costs on the return migration during the next reproductive season.

In the Mediterranean sea, North African shores such as the Tunisian and Libyan coasts, have been highlighted as a wintering area for both Caretta caretta and Chelonia mydas (Godley et al., 2002; Godley et al., 2003; Broderick et al., 2007 Rees et al., 2008). Furthermore there are reports that Turkish coasts are also selected as foraging grounds (Broderick et al., 2007). The data from the two tracked green turtle females that nested in Turkey show that both individuals chose to migrate to the foraging grounds mentioned above. These results emphasize that Turkish shores can serve as wintering areas for green sea turtles along with North African coasts. These results increase our knowledge of green turtle migrations in the Mediterranean and illustrate at least two strategies that post nesting females may use for their migrations to foraging areas in the region.

Acknowledgements: We thank Assoc. Prof. Oğuz Türkozan and Kelly Stewart for their aditional comments on this study, also Mr. Ali Osman Demirer for his efforts on the mapping processes and the Scientific Research Unit of Hacettepe University for the financial support of the second turtle tracking of the study.

BALAZS, G.H., P. CRAIG, B.R. WINTON & R.K. MIYA. 1994. Satellite telemetry of green turtles nesting at French Frigate Shoals, Hawaii, and Rose Atoll, American Samoa. In: K.A. Bjorndal, A.B. Bolten, D.A. Johnston & P.J. Eliazar (Comps.). Proceedings of the 14th Annual Symposium on Sea Turtle Biology and Conservation. NOAA Tech Memo. NMFS-SEFSC-351. p. 184-187.

BENTIVEGNA, F. 2002. Intra-Mediterranean migrations of loggerhead sea turtles (Caretta caretta) monitored by satellite telemetry. Marine Biology 141:795-800.

BENTIVEGNA, F., F. VALENTINO, P. FALCO, E. ZAMBIANCHI & S. HOCHSCHEID. 2007. The relationship between loggerhead turtle (Caretta caretta) movement patterns and Mediterranean currents. Marine Biology 151: 1605-1614.

BJORNDAL, K.A. & A.B. BOLTEN. 1997. Developmental migrations of juvenile green turtles in the Bahamas. In: J.A. Keinath, D.E. Barnard, J.A. Musick & B.E. Bell (Comps.). Proceedings of the 15th Annual Symposium on Sea Turtle Biology and Conservation. NOAA Tech Memo. NMFS-SEFSC-387. p 338.

BOLTEN, A.B. & G.H. BALAZS. 1995. Biology of the early pelagic stage-the “lost year.” In: K.A. Bjorndal (Ed.), Biology and conservation of sea turtles, second edition. Smithsonian Institution Press, Washington, D.C. pp. 579-581.

BOLTEN, A. 2003. Active swimmers - passive drifters: the oceanic juvenile stage of loggerheads in the Atlantic system. In: A.B. Bolten & B.E. Witherington (Eds.), Loggerhead Sea Turtles. Smithsonian Institution Press, Washington D.C. pp. 63-78.

BOWEN, B.W., A.B.MEYLAN, J.P. ROSS, C.J. LIMPUS, G.H. BALAZS & J.C. AVISE. 1992.Global population structure and natural history of the green turtle (Chelonia mydas) in terms of matriarchal phylogeny. Evolution 46: 865-881.

BRODERICK, A.C., M.S. COYNE, W.J. FULLER, F. GLEN & B.J. GODLEY. 2007. Fidelity and over-wintering of sea turtles. Proceedings of the Royal Society B. 274: 1533-1578.

CARDONA, L., M. REVELLES, C. CARRERAS, M. SAN FELIX, M. GAZO & A. AGUILAR. 2005. Western Mediterranean immature loggerhead turtles: habitat use in spring and summer assessed through satellite tracking and aerial surveys. Marine Biology 147: 583–591.

CARR, A.F., M.H. CARR, & A.B. MEYLAN. 1978. The ecology and migrations of sea turtles 7, the west Caribbean green turtle colony. Bulletin of the American Museum of Natural History 162: 1-48.

CARRERAS, C., M. PASCUAL, L. CARDONA, A. AGUILAR, D. MARGARITOULIS,A.REES,O.TURKOZAN,Y. LEVY,A.GASITH, M. AUREGGI, & M. KHALIL. 2007. The genetic structure of the loggerhead sea turtle (Caretta caretta) in the Mediterranean as revealed by nuclear and mitochondrial DNA and its conservation implications. Conservation Genetics 8: 761-775.

ECKERT, S.A., D. BAGLEY, S. KUBIS, L. EHRHART, C. JOHNSON, K. STEWART & D. DEFREESE. 2006. Internesting and postnesting movements and foraging habitats of leatherback sea turtles (Dermochelys coriacea) nesting in Florida. Chelonian Conservation & Biology 5: 239-248.

ENCALADA, S.E., K.A. BJORNDAL, A.B. BOLTEN & E. AL. 1998. Population structure of loggerhead turtle (Caretta caretta) nesting colonies in the Atlantic and Mediterranean regions as inferred from mtDNA control region sequences. Marine Biology 130: 567-575.

GODLEY, B.J., S. RICHARDSON, A.C. BRODERICK, M.S. COYNE, F. GLEN & G.C. HAYS. 2002. Long-term satellite telemetry of the movements and habitat utilisation by green turtles in the Mediterranean. Ecography 25: 352-362.

GODLEY, B.J., A.C. BRODERICK, F. GLEN & G.C. HAYS. 2003. Post- nesting movements and submergence patterns of loggerhead marine turtles in the Mediterranean assessed by satellite tracking. Journal of Experimental Marine Biology and Ecology 287: 119-134.

HATASE, H., Y., MATSUZAWA, W., SAKAMOTO, N. BABA & I. MIYAWAKI. 2002. Pelagic habitat use of an adult Japanese male loggerhead turtle Caretta caretta examined by the Argos satellite system. Fisheries Science 68: 945-947.

HAYS, G.C., P. LUSCHI, F. PAPI, C. DEL SEPPIA & R. MARSH. 1999. Changes in behaviour during the inter-nesting period and post-nesting migration for Ascension Island green turtles. Marine Ecology Progress Series 189: 263-273.

HENDRICKSON, J.R. 1958. The green turtle Chelonia mydas in Malaya and Sarawak. Proceedings of the Zoological Society of London 130: 455-535.

LIMPUS, C.J., J.D. MILLER, C.J. PARMENTER, D. REIMER, N. MCLACHLAN & R. WEBB. 1992. Migration of green (Chelonia mydas) and loggerhead (Caretta caretta) turtles to and from Eastern Australian rookeries. Wildlife Research 19: 347-358.

LUSCHI, P., G.R., HUGHES, R. MENCACCI, E. DE BERNARDI, A. SALE, R. BROKER, M. BOUWER & F. PAPI. 2003. Satellite tracking of migrating loggerhead sea turtles (Caretta caretta) displaced in the open ocean. Marine Biology 143: 793-801.

MILLER, J.D. 1997. Reproduction in sea turtles. In: P.L. Lutz & J.A. Musick (Eds.). The Biology of Sea Turtles. CRC Press, Boca Raton, FL, pp 51-81.

MEYLAN, A.B., K.A. BJORNDAL & J. TURNER. 1983. Sea turtle nesting at Melbourne beach, Florida. II. Post-nesting movements of Caretta caretta. Biological Conservation 26: 79-90.

MUSICK, J.A. & C.J. LIMPUS. 1997. Habitat utilization and migration in juvenile sea turtles. In: P.L. Lutz & J.A. Musick (Eds.). The Biology of Sea Turtles. CRC Press, Boca Raton, FL. pp. 137-163.

NICHOLS, W.J., J. SEMINOFF, A. RESENDIZ, P. DUTTON & F.A. ABREU-GROBOIS. 2000. Using molecular genetics and biotelemetry to study life story and long distance movement: a tale of two stories. In: F.A. Abreu-Grobois, R. Briseño-Dueñas, R. Márquez-Millán & L. Sarti-Martínez (Comps.). Proceedings of the 18th Annual Symposium on Sea Turtle Biology and Conservation. NOAA Tech Memo. NMFS- SEFSC-436. pp. 102-103.

ORUC, A. 2001. Trawl fisheries in the eastern Mediterranean and their impact on marine turtles. Zoology in the Middle East 24:119-125.

REES, A.F., M. JONY, D. MARGARITOULIS & G.J. GODLEY. 2008. Satellite tracking of a green turtle, Chelonia mydas, from Syria further highlights importance of North Africa for Mediterranean turtles. Zoology in the Middle East 45: 49-54.

SHORT, F., T. CARRUTHERS, W. DENNISON & M. WAYCOTT. 2007. Global seagrass distribution and diversity: A bioregional model. Journal of Experimental Marine Biology and Ecology 350: 3-20.

VENIZELOS, L. & M. NADA. 2000. The exploitation of loggerhead and green turtles continues in Egypt. Marine Turtle Newsletter 87:12-13.

WITHERINGTON, B.E. 2002. Ecology of neonate loggerhead turtles inhabiting lines of downwelling near a Gulf Stream front. Marine Biology 140: 843-853.