Warmer beaches skew slightly more female hatchlings

Did you miss the first post about this investigation into the incubation temperatures of loggerhead sea turtle nests in the Florida panhandle? No worries, check it out here!

By Megan Lamb, Guest Blogger

In 2016, I began looking at incubation temperatures, the amount of metabolic heating going on in an egg clutch, of loggerhead sea turtle nests and the overall temperature regime of the beach in Little St. George Island. After two years’ worth of nest data and one year of beach data, my results show the temperature regimes during the two years were very different.

Loggerhead nest
Temperature loggers are small and don’t interfere with nest incubation

The average middle third of incubation nest temperature (remember it’s that period where the sex is determined) in 2016 was 31.52 (±0.59)°C and in 2017 was 30.09 (±0.23)°C, significantly cooler. The other interesting part about nest data is that there is no statistical difference in middle of incubation temperatures between early, middle, or late nests in 2017. (Hurricane Hermine wiped out all my late season nests in 2016 so I couldn’t compare those nests). Average metabolic heating was 1.85 (±0.26)°C but there was quite a range in metabolic heating, from 0.72°C to 3.22°C. Finally, the transects show that the top of the dune was significantly warmer than the rest of the beach area, but there was no difference between any areas in the foreshore.


So, what does this all mean?

It looks like Little St. George is producing somewhat to very female-skewed hatchlings depending on the year. The warmer area on top of the dune is probably producing more females, and this area is also the least likely to get washed over by any storm surges. Conversely, the foreshore area, which is somewhat cooler and may be contributing more males, is more likely to get washed over. This pattern would further drive the beach to produce more females. I don’t have enough data yet to relate metabolic heating to clutch size but plan to look at that in the future.

I hope to continue this research over several more years so I can get a better picture of the temperature variation under different yearly climatic conditions. While the nest temperature data is specific to the island, I hope that understanding the relationship between beach temperatures, nest temperatures, and metabolic heating amounts can help more closely predict what temperatures nests on other beaches are incubating at in a less invasive way.

This research is being conducted under Florida Fish & Wildlife Conservation Commission Marine Turtle Permit #144. This project is funded in part by the Apalachicola NERR and in part by a grant awarded from the Sea Turtle Grants Program. The Sea Turtle Grants Program is funded from proceeds from the sale of the Florida Sea Turtle License Plate. Learn more at www.helpingseaturtles.org.

Photo of Megan
Megan Lamb, Environmental Scientist II at ANERR

Megan Lamb is an Environmental Specialist at the Apalachicola NERR and the lead for the NERR’s SWMP nutrient and chlorophyll-a sampling program. She also enjoys studying oyster bar communities, estuarine water quality and anthropogenic effects on estuaries, and sea turtle nesting dynamics. She is also completing her master’s degree in Fisheries and Aquatic Sciences at the University of Florida’s School of Forest Resources and Conservation.

One Comment Add yours

  1. Debbie Dix says:

    So interesting! Thanks for sharing.

    Liked by 1 person

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