Temperature data

Temperatures are crucial for the successful embryonic development of sea turtles, so at MEMANTA we measure them both in our hatchery and on the beach four times a day. This gives us the chance to adjust the incubation conditions when needed and understand better what effects human interaction in this otherwise natural process has.

So let’s look at some interesting results and the awesome temperature graphs that our interns made!

2023: Hatchery vs. Beach

In 2023, all of our nests were dug in the ground (no bags) and located in partial to full shade of varying degrees.
2023 was officially declared an El Niño year, resulting in less rain and elevated temperatures.

You can click on this image to make it larger.

  • The yellow and green lines are the beach temperatures (full sun), the others are our hatchery temperatures (shade and 30 metres inland) and the light blue line is the air temperature (shade).
  • The blue spikes rising from the bottom represent rain and you can see perfectly how the temperatures drop after major rain events.
  • The red horizontal line marks “danger – it’s getting too hot” (= Upper Limit) and the purple horizontal like marks the perfect temperature for development and a balanced sex ratio (= Pivotal Temperature)

Here is a direct comparison between the beach temperatures (left) and the hatchery temperatures (left) so you can see the effects of our shading! WOW!

Now let’s look at the 2024 graphs which are a liiiiiiittle bit different.

2024: Hatchery vs. Beach

In 2024 we had a wild mix in the hatchery: The majority were ground nests in partial to full shade, but we also had a couple of nests in the sun and bag nests both in the shade and in the sun.

Here again is a direct comparison between the beach temperatures and the hatchery temperatures.

Beach temperatures (left) vs. Nest temperatures in the hatchery (right)

Now there are several things we can conclude here:

  1. In times of rain or dense clouds, the temperatures are very similar. During dry and sunny periods, however, the differences are significant!
  2. Without rain, the beach temperatures are way above the pivotal temperature, resulting in a female-biased sex ratio. The very high daytime temperatures of up to 40°C could result in higher embryonic mortality – but we’ve never done the reality check here in Venecia as zero nests are left in their original spot on the beach and we don’t know what the natural hatching success would be.
  3. While the beach temperatures are mostly above 30°C, the nest temperatures in the hatchery usually stay around 28-30°C. So if I had to make a very rough guess, I’d say that our overall sex ratio is 60-70% male and 30-40% female.

Please keep in mind: These temperature measurements are only an approximation because the temperatures are measured in a depth of about 10cm (above the upper egg). The further down we go, the sand gets cooler, but in the centre of the nest it should be a bit warmer due to metabolic heating.

Individual nest data

Now let’s have a look at a few of the individual nests that we measured.
In the following graphs, the red-shaded area represents the middle third of the incubation period when the sex determination happens! So by looking at the temperatures within that period, we can make a rough guess about the sex ratio.

Nest A9 (shade) 17.July-07.September:
This nest showed perfect temperatures of around 29 to 30°C, resulting in a relatively balanced sex ratio.
Nest E7 (shade) 10.August-27.September:
Because of regular thunderstorms in this period, temperatures were a bit lower than 30°C and thus favouring females.
Nest K3 (sun) 28.September-15.November:
This nest showed female-favouring temperatures, but did never present dangerously hot temperatures even though there was basically no rain during the unusual dry period in October.
M5 (sun) 20.October-03.December:
Even though the temperatures were quite balanced at first, they dropped significantly when the big rain hit, so this is a tough one when guessing the sex ratio.

Now compare M5 with Bag 16 (they have roughly the same incubation period as they were laid just 4 days apart!) to see the differences between ground nests and bag nests:

Bag 16 (sun) 24.October-11.December:
This nest had its sex determination period when the big rain hit. You can see that the differences between day and night temperatures are bigger than in M5, following the up’s and down’s of the daily air temperatures.

And now one last bag nest because we can’t get enough of these temperature graphs!

Bag 1 (partial shade) 05.September-27.October:
Because the sex determination period was after a major rain event, the temperatures of this nest were male-favouring.

Outcome

So what are our conclusions for this upcoming season 2025/26??

  • We should locate even more nests in the sun to slightly reduce the percentage of male-favouring nests and achieve a more balanced, 50/50 sex ratio.
  • Bag nests should be located in the sun or in partial shade as they are generally cooler than ground nests.
  • However, temperatures in the sun need consistent observation to make sure the sand doesn’t get too hot, especially during prolonged dry, sunny periods.