Pivotal temperature for loggerhead turtles (Caretta caretta) from Kyparissia Bay, Greece

Abstract

Pivotal temperature (the constant temperature giving 50% of each sex) for two clutches of loggerhead sea turtles (Caretta caretta) from Kyparissia Bay, Greece, was 29.3°C. Pivotal incubation duration (the time from laying to hatching giving 50% of each sex) was 52.6 days. These values are close to those obtained for this species in Brazil and the United States, providing further evidence that these characteristics are relatively conservative in different populations. Methodological differences between different experiments and limitations on accuracy of equipment make the detection of small differences problematic. Comparison of incubation durations in the field with the pivotal durations obtained here suggest that hatchling sex ratio on some Mediterranean beaches is female biased but probably varies considerably within this region.Résumé : La température charnière (la température constante d'incubation qui produit 50 % d'individus de chaque sexe) pour deux masses d'oeufs de caouanes (Caretta caretta) de la baie de Kyparissia en Grèce a été estimée à 29,3°C. La durée charnière de l'incubation (le temps entre la ponte et l'éclosion qui produit 50 % de tortues de chaque sexe) est de 52,6 jours. Ces valeurs se rapprochent de celles que l'on a obtenues chez cette espèce au Brésil et aux É.-U., ce qui est une indication supplémentaire que ces caractéristiques sont relativement conservatrices dans les diffé-rentes populations. Les différences méthodologiques entre les expériences et les limites de précision des appareils rendent problématiques la détection de petites différences. La comparaison des durées de l'incubation en nature avec les durées charnières obtenues ici laisse croire que le rapport mâles : femelles chez les nouveau-nés sur certaines plages méditerranéennes favorise les femelles, mais qu'il varie probablement beaucoup dans la région.[Traduit par la Rédaction] Mrosovsky et al. 2124

Sex ratio estimations of loggerhead marine turtle hatchlings by incubation duration and nest temperature at Sirte beaches (Libya)

“…The first used the mean temperature during the middle third of the incubation period, while the second used the incubation duration. The curves used for estimation of sex ratio as functions of incubation duration and temperature during the second third of the incubation duration were those of Mrosovsky et al (2002) adapted to the field. The sex ratio curve (% of females) as a function of the mean temperature during the second third of incubation duration was adapted to the field by adding 0.4°C (Mrosovsky et al 2002), which corresponds to the difference between ambient temperature and egg temperature (Fig.…”

“…2). The sex ratio curve (% of females) as a function of incubation duration (Mrosovsky et al 2002) was also adapted to the field by adding 4 days, which corresponds to the interval between hatching and the emergence of hatchlings at the sand surface (Fig. 3).…”

Predicting the impacts of climate change on a globally distributed species: the case of the loggerhead turtle

“…Further work using laboratory incubation suggested that the response of loggerhead turtle eggs to temperature was fairly conserved, at least in terms of pivotal temperature -the temperature that produces a 1:1 sex ratio (Mrosovsky and Pieau, 1991), across different populations from different latitudes in the northwest Atlantic (Mrosovsky, 1988). Subsequent studies of laboratory incubation of loggerhead turtle eggs from Brazil and Greece have also found pivotal temperatures that are relatively similar -close to 29°C (Marcovaldi et al, 1997;Mrosovsky et al, 2002). Thus, variation in sex ratios observed in the wild is thought to be driven largely by local environmental conditions, specifically egg temperatures during incubation (Godfrey and Mrosovsky, 2001).…”

Behaviour analysis of the loggerhead sea turtle Caretta caretta from direct in-water observation

“…This bias towards female turtles partly reflects their location closer to shore where surveys were concentrated. However this ratio may also reflect the highly skewed bias towards females found in hatchling loggerhead turtles in Mediterranean populations (Godley et al 2001, Mrosovsky et al 2002). …”