Sea turtles lay their eggs in underground nests on sandy beaches. The eggs are then left to incubate unattended and are subject to a suite of environmental conditions. The interplay of these environmental variables affects important factors such as the development rate and hatch success of the nest.
Since sea turtles exhibit temperature-dependent sex determination, the incubation temperature of the egg also determines the sex of the offspring. Warm incubation temperatures (typically above 29 °C) lead to a majority of females being born whereas cooler temperatures lead to males being born.
A new study published recently in Endangered Species Research shows the importance of rainfall throughout the incubation process. The researchers from Florida Atlantic University (USA) recorded rainfall and sand temperatures at a loggerhead turtle nesting beach in Florida. Ms Lolavar, the lead author of the study, tells me that the results of the study show that “heavy rainfall events can cool the sand and bring the incubation temperature of a nest in the male-producing range. However, if beach temperatures are too warm, which is often the case in Florida, most rainfall events don’t shift the nest temperature enough to produce males.”
This is not a phenomenon limited to Florida of course. A 2007 study of leatherbacks nesting in Grenada showed similar results. What sets the new research apart is that the Florida researchers also determined the sex of hatchling sea turtles laparoscopically. This enabled them to empirically show that during particularly rainy nesting seasons more male turtles hatched.
Ultimately, this study shows that understanding the effect of rainfall on incubation temperatures is key to anticipating the effects of the changing climate on sex ratios, and thus for the successful long-term conservation of sea turtles.
Loggerhead hatchlings: are they female or male?
The Cape Verdean national military offers its support to SOS Tartarugas and patrols the beaches at night to protect the nesting turtles from poachers. This means that during nightly patrols you sometimes meet a military fireteam on the beach. Most often, the unit will just stay in one spot and stay there throughout the night. Other times they will patrol with you in the hope of seeing turtles. And occasionally they show a real interest in your work and want to help.
One night I found a turtle nest that had to be relocated. Unfortunately I had just missed the nesting turtle so I did not see her. I started to dig for the eggs and this raised the curiosity of two military soldiers that were nearby. They watched me dig with interest and when I started to extract the eggs from the egg chamber they looked very surprised and left in haste only to come back moments later armed with their AK-47 assault riffles. They seemed to take the protection of the turtle eggs very seriously and stood sentinel over me!
When I was done removing the eggs from the nest I carried them down the beach to a good location to rebury them. Both soldiers followed me, guarding me and the turtle eggs. I had my own personal military escort! When I was done relocating the eggs they both saluted me and marched off. I then carried on with my patrol. It makes me very happy to know that some people take the preservation of their natural heritage very seriously.
Every once in a while you see an adult sea turtle with missing limbs. This can be due to several reasons: it may be that the turtle had a close encounter with a shark; it may be that a motorboat inadvertently struck the turtle; or it may be that the turtle was born with a missing limb.
Last night I saw such a turtle. I was patrolling a beach on the east coast of the island when I came across an interesting asymmetrical turtle track. I carefully followed the track and found a turtle that was missing a back flipper. She was trying to dig an egg chamber to lay her eggs.
What is very curious is that the turtle still went through all of the regular nesting motions and seemed completely oblivious to the fact that she had a missing flipper. She dug with her flipper, scooped some sand up, removed it from the nest cavity, and then shifted her body to dig with her missing flipper. Of course she could not dig with her missing flipper but still went through the ghost motions before shifting her body again and digging with her flipper. After several minutes the turtle decided to give up on this egg chamber as she judged it was not going well enough.
Luckily, the turtle decided to try to dig a new nest further up the beach. I discretely followed her and opted to help her out this time: as the turtle was digging, every time she shifted her body and tried to dig with her missing limb, I would reach in the nest cavity and scoop out some sand for her. Together we built a nice egg chamber and the turtle seemed pleased as she resolved to lay her eggs! She lay close to 80 eggs that all fit nicely in our egg chamber. After covering up her nest and camouflaging the nesting area, I watched her return to the sea. Due to her missing limb, she walked a little bit sideways like a crab.
This particular turtle had been tagged earlier this season and was spotted nesting twice already. I imagine that the other rangers that saw her nest also gave her a helping hand when she was digging!
It is possible to adopt sea turtles at the SOS Tartarugas Conservation Centre. You can adopt individual hatchlings, entire nests, and adult nesters. Of course this is a symbolic adoption and you do not get to take the sea turtle home with you, but you would be surprised of how many times I have been asked things like: “What should I feed my baby sea turtle when I am back home?”
For example, if you adopt an adult nester, you can choose a name for your turtle and will receive a personalized Adoption Certificate. Your turtle will be tagged and you will receive her unique tag numbers. Every time your turtle comes ashore you will be informed by e-mail and will receive relevant information such as if she nested and how many eggs she laid!
If you are interested in adopting a sea turtle you can visit the SOS Tartarugas website. Adopting a sea turtle is a very nice gesture and can be a special present for a loved one! It is also a great way to show your support for the project and the conservation of loggerheads in Cape Verde.
The day after a nest hatches, nest excavations are carried out. This is done for two main reasons:
- it allows hatchlings that were unable to make it out of the nest on their own to be released
- it enables the calculation of the success rate of each nest
Not all eggs develop into fully formed live hatchlings. Sometimes eggs are infertile, sometimes eggs fail during development, and sometimes hatchlings suffocate at the bottom of the nest. This happens for nests in the hatchery and for nests incubating naturally on the beach. The success rate of a nest is given as the number of live hatchings out of the nest against the total number of eggs in the nest.
Quantifying the success rate of a nest can be very informative scientifically. As part of my research I am trying to see if there is a relationship between the success rate of a nest and environmental variables such as sand temperature and rainfall.
As well as being scientifically informative, a nest excavation is also an exciting time and attracts many tourists because of the live hatchlings that are excavated from the nests. The opportunity to see wild baby sea turtles is unique. They are quite an amazing sight!
Hatchlings usually wait for nighttime to emerge from the sand. The temperatures are cooler and they can reach the sea under the cover of darkness. Something quite unique happened yesterday at the hatchery: a nest emerged in the late afternoon!
First a hatchling popped his head out of the sand. Then a flipper. Then another hatchling showed his face. And another. And before you know it, dozens of little hatchlings were crawling out of the sand! It was very special to see.
The hatchlings were full of energy and scattered around the hatchery. We collected them, counted them carefully, and released them altogether afterwards. It is quite rare to see this happen during the day so everyone present felt very lucky!
Turtle nests are sometimes relocated to the hatchery. The hatchery is a place where the eggs are kept safe from predators and where they can incubate naturally. It is a pretty unique place, in that when you are walking around the hatchery you know that there are literally thousands of turtle eggs developing into hatchlings just under your feet!
Each nest is carefully labelled and the due date is recorded. Several days before the nest is due to hatch a circular cage is placed atop the nest so that when the hatchlings emerge from the sand they do not scatter everywhere. During the night, a ranger will check the nests every hour so that he can immediately release any hatchling that emerge from the sand. The hatchlings are brought to the top of a beach and are released. They then reach the sea on their own.
Sleeping in the hatchery and releasing the hatchlings is something that I have not yet done. Hopefully I can do this before the end of my stay!