Sex ratio estimations of Cheloniamydas hatchlings at Samandağ Beach, Turkey

Sex ratio estimations of Cheloniamydas hatchlings at Samandağ Beach, Turkey

Samandağ Beach, an important nesting location for endangered green turtles (Chelonia mydas), is located at the most eastern part of the Mediterranean in Turkey. Hatchling sex ratio can be one of the key factors for green turtle protection, which is under the threat of global climate change. In this study, sex ratios of hatchlings were estimated by histological examination of dead hatchlings (n = 190) and by nest temperatures (n = 14) at Samandağ Beach between the 2003 and 2007 nesting seasons. The histological examination of dead C. mydas hatchlings and temperature-recorded nests indicated a female-biased sex ratio on Samandağ Beach. By histological examination, top and bottom levels of nests were recorded as 94% and 64% of females. Sex ratios during the middle third of the incubation period ranged from 39% to 97% for females with a mean of 74%. Distance from the sea was correlated with the middle third of incubation temperature (r = 0.604, P = 0.022) and female ratio (r = 0.573, P = 0.032). While nest temperatures and nest parameters such as hatching success, clutch size, nest distance from the sea and from vegetation, nest depth, and the day of emergence were not found significantly different among years (P > 0.05), incubation duration was found significantly different among years (P < 0.05). The results showed a female-dominated sex ratio by both histology and nest temperature. The knowledge of hatchling sex ratios provides information on demographic parameters, and coupled with appropriate conservation measures this can make important contributions to studies of climate change effects on green sea turtle populations.

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  • Ackerman RA (1997). The nest environment and the embryonic development of sea turtles. In: Lutz PL, Musick JA, editors. The Biology of Sea Turtles.
  • Boca Raton, FL, USA: CRC Press, pp. 83-106.Başkale E, Kaska Y (2005). Sea turtle nest conservation techniques on southwestern beaches in Turkey. Israel J Zool 51: 13-26.
  • Broderick AC, Godley BJ, Hays GC (2001). Metabolic heating and the prediction of sex ratios for green turtles (Chelonia mydas). Physiol Biochem Zool 74: 161-170.
  • Broderick AC, Glen F, Godley BJ, Hays GC (2002). Estimating the number of green and loggerhead turtles nesting annually in the Mediterranean. Oryx 36: 227-235.
  • Broderick AC, Godley BJ, Reece S, Downie JR (2000). Incubation periods and sex ratios of green turtles: highly female biased hatchling production in the eastern Mediterranean. Mar Ecol Prog Ser 202: 273-281.
  • Bull JJ (1980). Sex determination in reptiles. Q Rev Bid 55: 3-21.
  • Casale P, Gerosa G, Yerli SV (2000). Female-biased primary sex ratio of the green turtle, Chelonia mydas, estimated through sand temperatures at Akyatan, Turkey. Zool Middle East 20: 33-42.
  • Godfrey MH, Barreto R, Mrosovsky N (1997). Metabolically generated heat of developing eggs and its potential effect on sex ratio of sea turtle hatchlings. J Herpetol 31: 616-619.
  • Godfrey M, Mrosovsky N (1999). Estimating hatchling sex ratios. In: Eckert KL, Bjorndal KA, Abreu Grobois FA, Donnelly M, editors. Research and Management Techniques for the Conservation of Sea Turtles. IUCN MTSG. Publication No. 4. Gland, Switzerland: IUCN, pp. 136-138.
  • Hawkes LA, Broderick AC, Godfrey MH, Godley BJ (2007). Investigating the potential impacts of climate change on a marine turtle population. Glob Change Biol 13: 923-932.
  • Hays GC, Ashworth JS, Barnsley MJ, Broderick AC, Emery DR, Godley BJ, Henwood A, Jones EL (2001). The importance of sand albedo for the thermal conditions on sea turtle nesting beaches. Oikos 93: 87-94.
  • Hays GC, Broderick AC, Glen F, Godley BJ (2003). Global change and sea turtles: a 150-year reconstruction of incubation temperatures at a major marine turtle rookery. Glob Change Biol 9: 642-646.
  • Hays GC, Godley BJ, Broderick AC (1999). Long-term thermal conditions on the nesting beaches of green turtle on Ascension Island. Mar Ecol Prog Ser 185: 297-299.
  • Houghton JD, Hays GC (2001). Asynchronous emergence by loggerhead turtle (Caretta caretta) hatchlings. Naturwissenschaften 88: 133-136.
  • Janzen FJ (1994a). Population biology, climate change and temperature-dependent sex determination in reptiles. P Natl Acad Sci USA 91: 7487-7490.
  • Janzen FJ (1994b). Vegetational cover predicts the sex ratio of hatchling turtles in natural nest. Ecology 75: 1593-1599.
  • Janzen FJ, Paukstis GL (1991). Environmental sex determination in reptiles – ecology, evolution, and experimental design. Q Rev Biol 66: 149-179.
  • Kaska Y, Downie R (1999). Embryological development of sea turtles (Chelonia mydas, Caretta caretta) in the Mediterranean. Zool Middle East 19: 55-69.
  • Kaska Y, Downie JR, Tippett R, Furness R (1998). Natural temperature regimes for loggerhead and green turtle nests in the eastern Mediterranean. Can J Zoolog 76: 723-729.
  • Kılıç Ç, Candan O (2014). Hatchling sex ratio, body weight and nest parameters for Chelonia mydas nesting on Sugözü beaches (Turkey). Anim Biodivers Conserv 37: 177-182.
  • Mazaris AD, Vokou D, Almpanidou V, Türkozan O, Sgardelis SP (2015). Low conservatism of the climatic niche of sea turtles and implications for predicting future distributions. Ecosphere 6: 1-12.
  • Mrosovsky N (1988). Pivotal temperatures for loggerhead turtles (Caretta caretta) from northern and southern nesting beaches. Can J Zoolog 66: 661-669.
  • Mrosovsky N (1994). Sex ratios of sea turtles. J Exp Zool 270: 16-27.
  • Mrosovsky N (2006). Distorting gene pools by conservation: assessing the case of doomed turtle eggs. Environm. Manag. 38: 523-531.
  • Mrosovsky N, Bapistotte C. Godfrey MH (1999). Validation of incubation durations as an index of sex ratio of sea turtle hatchlings. Can J Zoolog 77: 831-835.
  • Mrosovsky N, Yntema CL (1980). Temperature dependence of sexual differentiation in sea turtles: implications for conservation practices. Biol Conserv 18: 271-280.
  • Öz M, Erdoğan A, Kaska Y, Düşen S, Aslan A, Sert H, Yavuz M, Tunç MR (2004). Nest temperatures and sex-ratio estimates of loggerhead turtles at Patara beach on the southwestern coast of Turkey. Can J Zoolog 82: 94-101.
  • Özdemir B, Türkozan O (2006). Hatching success of original and hatchery nest of the green turtle, Chelonia mydas, in Northern Cyprus. Turk J Zool 30: 377-381.
  • Özdilek HG, Yalçın-Özdilek Ş, Ozaner FS, Sönmez B (2006). Impact of accumulated beach litter on Chelonia mydas L. 1758 (green turtle) hatchlings of the Samandağ Coast, Hatay, Turkey. Fresen Environ Bull 15: 95-103.
  • Sönmez B, Turan C, Yalçın Özdilek Ş (2011). The effect of relocation on the morphology of green turtle, Chelonia mydas (Linnaeus, 1758) hatchling on Samandağ beach, Turkey. Zool Middle East 52: 29-38.
  • Sönmez B, Yalçın Özdilek Ş (2013). Conservation technique of the green turtle (Chelonia mydas L. 1758) nests under the risk of tidal inundation with hatcheries, on Samandağ beach, Turkey. Russ J Herpetol 20: 19-26.
  • Spotila JR, Standora EA, Morreale SJ, Ruiz GJ (1987). Temperature dependent sex determination in the green turtle (Chelonia mydas): effects on the sex ratio on a natural nesting beach. Herpetologica 43: 74-81.
  • Türkozan O, Ilgaz Ç, Taşkavak E, Özdemir A (2003). Hatch rates of loggerhead turtles and physical characteristics of the beach at Fethiye, Turkey. J Mar Biol Assoc UK 83: 231-232.
  • Türkozan O, Kaska Y (2010). Turkey. In: Casale P, Margaritoulis D, editors. Sea Turtles in the Mediterranean: Distribution, Threats and Conservation Priorities. Gland, Switzerland: IUCN, pp. 257-293.
  • Türkozan O, Yılmaz C (2007). Nest relocation as a conservation strategy: looking from a different perspective. Marine Turtle Newsletter 118: 6-8.
  • Yalçın-Özdilek Ş (2007). Status of sea turtles (Chelonia mydas andCaretta caretta) on Samandağ Beach, Turkey: evaluation of five-year monitoring study. Ann Zool Fenn44: 333-347.
  • Yalçın-Özdilek Ş, Özdilek HG, Ozaner FS (2007). Possible influence of beach sand characteristics on green turtle nesting activity on Samandağ Beach, Turkey. J Coastal Res 23: 1379-1390.
  • Yalçın-Özdilek Ş, Özdilek HG, Sangün K (2006). The effects of some elements (Ca, Mg and Cr) on the nesting activity of green turtles that nest on the Samandağ Beach, Turkey. Fresen Environ Bull 15: 1607-1615.
  • Yalçın-Özdilek Ş, Sönmez B (2006). Some properties of new nesting areas of sea turtles in northeastern Mediterranean situated on the extension of the Samandağ Beach, Turkey. J Environ Biol 27: 537-544.
  • Yalçın-Özdilek Ş, Sönmez B (2011). Nesting characteristics at Samandağ and extended beaches, Turkey. Marine Turtle Newsletter 131: 7-9.
  • Wyneken J, Burke TJ, Salmon M, Pedersen DK (1988). Egg failure in natural and relocated sea turtle nests. J Herpetol 22: 88-96.
  • Yntema CL, Mrosovsky N (1980). Sexual differentiation in hatchling loggerheads (Caretta caretta) incubated at different controlled temperatures. Herpetologica 36: 33-36.