Loggerhead turtle--Nests

Because of the logistics involved with field experiments, most of what is known about effects of temperature on the nest environment of loggerhead (Caretta caretta) sea turtles has been learned in the laboratory. Until now, scientists have been forced to speculate on what effects different sands might have on temperature within the nest. Results of the present study indicate that the upper lethal temperature limit of loggerheads is between 33-35C; this temperature is more likely to be reached in larger clutches, causing high mortality and low emergence success. Furthermore, the metabolic heat of a larger clutch will be exacerbated by warmer sand types. Ranges of temperatures experienced during the middle period of incubation, not only within the clutch, but over the course of the nesting season, are both above and below the pivotal temperature for sex determination in loggerheads. Perhaps it is inappropriate to use mean beach temperatures to predict outcomes of sex ratios on various coasts. It would be more prudent to concern ourselves with predicting survivorship of a clutch using results from this field study along with beach temperatures, rather than using laboratory temperatures to predict sex ratios.

The sex ratios of hatchling loggerheads (Caretta caretta) were determined to provide robust assessments of regional and seasonal contributions of males and females to the population. Hatchlings from nests along the Atlantic coastline were raised to 120 g, sexed laparoscopically and verified histologically. Sex ratios differed at the beach, subseason, and subpopulation levels. There was no difference in overall sex ratios between the two study years. Average nest temperature and incubation durations were not accurate sex ratio correlates. Temperatures that produced female biased or male biased sex ratios overlapped in ranges with those producing a single sex. I found that the Transitional Range of Temperatures for loggerhead sea turtles is approximately 26.5°C--32°C, and the best correlation between average temperature and sex ratio occurred at 50--65% of incubation. Further studies are needed to define the roles of other environmental factors or the responses of tissues in loggerhead sex determination.