AB 18:9-19 (2013)  -  DOI: https://doi.org/10.3354/ab00475

Estimating sex ratios in Caribbean hawksbill turtles: testosterone levels and climate effects

Lucy A. Hawkes1,2, Andrew McGowan1, Brendan J. Godley1, Shannon Gore3, Anke Lange4, Charles R. Tyler4, Damon Wheatley5, Jim White5, Matthew J. Witt1, Annette C. Broderick1,*

1Centre for Ecology & Conservation, College of Life and Environmental Sciences, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK
2School of Biological Sciences, Brambell Laboratories, Bangor University, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK
3Conservation and Fisheries Department, Ministry of Natural Resources and Labour, PO Box 3323, Road Town, Tortola, British Virgin Islands
4Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, UK
5The Settlement, Anegada, British Virgin Islands
*Corresponding author. Email:

ABSTRACT: Evolutionary theory predicts that male and female offspring should be produced at a 1:1 ratio, but this may rarely be the case for species in which sex is determined during incubation by temperature, such as marine turtles. Estimates of primary sex ratio suggest that marine turtle sex ratios are highly skewed, with up to 9 females per male. We captured juvenile hawksbill turtles Eretmochelys imbricata in waters around Anegada, British Virgin Islands, a regionally important foraging aggregation, and analysed concentrations of plasma testosterone and oestradiol-17β from 62 turtles to estimate sex ratio. There were 2.4 to 7.7 times more females than males. Testosterone concentrations correlated with sampling date and sea surface temperature (SST), with higher concentrations in the late summer when SST was highest, suggesting that assigning sex through threshold values of sex hormones must be carried out cautiously. The sex ratio in the juvenile foraging aggregation around Anegada is more male biased than at other locations, suggesting that turtles at Anegada have resilience against feminising effects of climate change. Future work should (1) integrate the relative contributions of different genetic stocks to foraging aggregations and (2) investigate the annual and seasonal cycles of sex hormones, and differences among individuals and life history stages.


KEY WORDS: Marine turtles · Sex ratio · Climate change · Hormones


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Cite this article as: Hawkes LA, McGowan A, Godley BJ, Gore S and others (2013) Estimating sex ratios in Caribbean hawksbill turtles: testosterone levels and climate effects. Aquat Biol 18:9-19. https://doi.org/10.3354/ab00475

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