Graeme C. Hays

Abstract

Climate warming and the feminization of populations due to temperature-dependent sex determination may threaten sea turtles with extinction. To identify sites of height-ened  risk,  we  examined  sex  ratio  data  and  patterns  of  climate  change  over  multi-ple   decades for   64   nesting sites    spread across     the   globe.    Over    the   last   62 years the mean    change in  air  temperature was   0.85°C per   century (SD = 0.65°C, range = −0.53 to +2.5°C, n= 64    nesting sites).    Temperatures increased at  40   of  the   64   study    sites. Female-skewed hatchling or  juvenile sex   ratios    occurred at  57   of  the   64   sites,    with skews >90% female at 17 sites. We did not uncover a relationship between the ex-tent of warming and sex ratio (r62= −0.03, p= .802, n= 64    nesting sites).    Hence, our results  suggest  that  female-hatchling  sex  ratio  skews  are  not  simply  a  consequence  of recent warming but have likely persisted at some sites for many decades. So other factors  aside  from  recent  warming  must  drive  these  variations  in  sex  ratios  across  nesting sites, such as variations in nesting behaviour (e.g. nest depth), substrate (e.g. sand albedo), shading available and rainfall patterns. While overall across sites recent warming is not linked to hatchling sex ratio, at some sites there is both is a high female skew    and   high    warming, such    as  Raine    Island    (Australia; 99%    female green    turtles; 1.27°C warming per century), nesting beaches in Cyprus (97.1% female green turtles; 1.68°C    warming per   century) and   in  the  Dutch    Caribbean (St  Eustatius; 91.5%    femaleleatherback turtles; 1.15°C warming per century). These may be among the first sites where management intervention is needed to increase male production. Continued monitoring  of  sand  temperatures  and  sex  ratios  are  recommended  to  help  identify  when high incubation temperatures threaten population viability.

Abstract

Reconstruction of past conditions provides important information on how ecosystems have been impacted by climate change, but generally for microhabitats worldwide there are no long-term empirical measurements. In these cases, there has been protracted debate about how various large-scale environmental proxies can best be used to reconstruct local temperatures. Here we help resolve this debate by examining how well environmental proxies hindcast sand temperatures at nest depths for five sea turtle nesting sites across the world. We link instrumental air temperature and sea surface temperature records with empirical sand temperature observations in the Atlantic (Ascension Island and Cape Verde), the Indian Ocean (Chagos Archipelago), the Caribbean (St Eustatius) and the Pacific (French Polynesia). We found strong correlations between sea surface temperatures, air temperatures and sand temperatures at all our study sites. Furthermore, Granger causality testing shows variations in sea surface temperature and air temperature precede variations in sand temperatures. We found that different proxies (air or sea temperature or a combination of both) predicted mean monthly sand temperatures within <0.5°C of empirical observations. Reconstructions of sand temperatures over the last 170 years reveal a slight warming of temperatures (maximum 0.5°C per century). An analysis of 36 published datasets revealed that the gradient of the relationship between sand temperature and air temperature is relatively constant, suggesting long-term changes in sand temperature could be extended around the world to include nesting sites where there are no empirical measurements of sand temperature. Our approaches are likely to have utility for a range of microhabitats where there is an interest in long-term changes in temperature.

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