In 2017, N.E.S.T. volunteers began placing temperature data loggers in all of our sea turtle nests. In 2018 we upgraded our technology to Bluetooth capable data loggers whereby N.E.S.T. volunteers could download hourly temperature data directly from the nest to their cell phones for real time data analysis. We intend to collect temperature data on our nests for several years. Our goal is to explore how real life nest temperatures impact incubation times and the viability of embryos and hatchlings. We hope the temperature data we collect will help nest parents and other volunteers better manage nests and further engage beach goers and turtle lovers in our cause.
As a starting point for our work, we looked at a number of scientific studies related to incubation temperatures of sea turtle nests. Researchers generally use constant incubation temperatures. We intend to compare real life situations where temperatures vary from hour to hour and day to day with the data gathered in those studies. Below is a brief summary of only some of the research on incubation temperatures for Atlantic loggerhead sea turtles.
- Optimal constant nest incubation temperatures are generally around 83 to 88˚F i.e. mid-range temperatures.
- Constant nest temperatures equal to or above 89 to 91˚F generally mean embryos do not hatch or hatch but do not survive
- Constant nest temperatures of 87.8˚F produced hatchlings with poor righting response times but normal swimming and crawl speeds.
- Constant nest temperatures equal to or below 75 to 77˚F generally mean embryos do not hatch
- Incubation temperatures at or below a constant 80.6˚F produce hatchlings with decreased vigor, poor righting response times, slow crawl speeds, and overall poorer swimming ability
- The variation of temperatures in natural nests may alter some of these effects
- The metabolic heating (from growth of embryos) that occurs in nests especially during the last half of incubation may alter these impacts.
Temperature-dependent Sex Determination (TSD)
Incubation temperatures are also important because the sex of a sea turtle is determined by the temperature of the nest during the second trimester of embryonic maturation. This is called temperature-dependent sex determination (TSD) and is common in reptiles. In our area for loggerhead sea turtles, the temperature where 50% of the embryos will be male and 50% will be female is around 84.6˚F. This is called the pivotal temperature. A mean temperature of 86.9˚F will result in 100% females and a mean temperature of 81.5˚F. will result in 100% males. As our climate changes and oceans warm, colder northern breeding grounds such as those covered by N.E.S.T. are important to providing sufficient numbers of male hatchlings to sustain and grow overall sea turtle populations.
At left is a chart of second trimester mean temperatures in ˚ Fahrenheit versus nest number (see http://www.nestonline.org/nests-hatchlings/active-nest-status/) of all our 2017 and 2018 nests that successfully hatched. The top red line indicates the temperature where all hatchlings will be female, 86.9˚F. The next red line indicates the pivotal temperature of 84.6˚F where the M/F split is 50-50. The bottom line shows a temperature of 81.5˚F where hatchlings will be 100% male.