MEPS 324:281-285 (2006)  -  doi:10.3354/meps324281

Sex ratios of juvenile loggerhead sea turtles Caretta caretta in the Mediterranean Sea

Paolo Casale1,*, Bojan Lazar2,3, Sara Pont4, Jesús Tomás5, Nicola Zizzo6, Ferran Alegre4, Javier Badillo5, Aldo Di Summa6, Daniela Freggi7, Gordana Lackovic8, Juan Antonio Raga5, Lucio Rositani9, Nikola Tvrtkovi´c2

1via Antonio Calderara 29, 00125 Roma, Italy
2Department of Zoology, Croatian Natural History Museum, Demetrova 1, 10000 Zagreb, Croatia
3Blue World Institute of Marine Research and Conservation, Kastel 24, 51551 Veli Losinj, Croatia
4Foundation for the Conservation and Recovery of Marine Animals, Camí Ral, 239 Premià de Mar, 08330 Barcelona, Spain 5Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, PO Box 22085, 46071 Valencia, Spain
6Department of Animal Health and Well-Being, University of Bari, SP per Casamassima km 3, 70010 Valenzano, Italy 7Sea Turtle Rescue Centre, WWF Italy, CP 92010 Lampedusa, Italy
8Department of Zoology, Faculty of Science, University of Zagreb, 6 Roosevelt Square, 10000 Zagreb, Croatia
9Laboratorio Biologia Marina Bari, Molo Pizzoli, Porto di Bari, 70100 Bari, Italy

ABSTRACT: Species with environmental sex determination may show sex ratios that differ from 1:1; therefore, sex ratio is an important variable when studying the population dynamics of these species. For instance, when estimating population size and productivity, sex ratio would be a required parameter. For endangered species, such as sea turtles, this is particularly important in order to understand the possible effects of human impacts and conservation measures. Unfortunately, only adult sea turtles show evident external sexual dimorphism; sex ratios are more difficult to obtain for the juvenile class, which represents the largest part of a population. Here we present the first extensive assessment of the sex ratio of juvenile loggerhead turtles Caretta caretta in the Mediterranean Sea. A total of 310 dead turtles from 4 different areas were sexed by direct examination of gonads, the most reliable sexing method. Females comprised 54.2% of the whole sample, and no significant differences were observed among study areas. However, this value cannot be ascribed to a single population, because specimens from different nesting sites—both within and outside the Mediterranean—share the same foraging areas, and each population may potentially contribute a different sex ratio. Although we recorded an unbiased sex ratio, our results were compatible with a hypothetical scenario in which Mediterranean nesting beaches produce a majority of females when other information from the region (distribution, mixed stocks and sex ratios) was considered.

KEY WORDS: Sex ratio · Caretta caretta · Mediterranean · Juvenile sea turtles

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