After just 5 days on a turtle conservation project in Cuyutlan Mexico, I have already had a chance to see the whole process of Olive Ridley turtles (Lepidochelys olivacea) nesting right through to hatchling release. I have been privileged to work with an amazing team of people totally dedicated to preserving these incredible animals. As we all know turtles are up against it, they are under pressure on so many fronts. Not only do they have some nasty predators such as Tiger sharks, but man is accidentally and deliberately hammering populations worldwide. They are caught in fishing nets, poisoned by plastic and other pollutants, caught for meat, their eggs stolen for the restaurant trade and their habitat decimated for beachfront housing and hotel development. Pretty difficult for animals that take an estimated 13-15 years to mature (according to ‘The Biology of Sea Turtles volume II’).
It really started 2 nights ago when I went out on the conservation group’s quad bike with one of the team, Daniel. We whizzed along the beach scanning the sand for tracks made by female turtles. At 23.10 just a few minutes into our patrol Daniel suddenly turned the bike through 180° and pointed to a set of tracks leading up the beach. In truth I had not even noticed them, it took a trained eye to spot the tell-tale signs.
We followed the tracks to a spot near the top of the beach and to my excitement there was an Olive Ridley turtle making a nest to lay her eggs. At this time in Mexico, before the rains, the sand is still very dry and in many places unsuitable for nest making. The sand keeps falling into the hole and the female eventually gives up and tries somewhere else, on occasions she may try 8 times without success and is eventually forced back to the sea due to exhaustion to try again another night.
On this night however, Daniel had brought some containers of water and we also had a reasonable source of extra water just 40 metres away, the sea. Daniel poured water round the back end of the turtle and she was then able to dig a suitable nest. It was surprisingly precise, using her back flippers like hands she alternated from one to the other. She scooped some sand into a flipper, lifted it out and flung the sand away from the hole. She dug a vertical tube like hole with a bowl at the bottom which was almost precisely 45 cm deep and then commenced to lay her eggs, 2 or 3 at a time. A liquid also followed the eggs into the nest and this acts as a natural antibiotic to help protect the eggs against disease.
The depth of the hole has to be precise because turtles have temperature dependent sex determination (TSD) i.e. temperature affects the ratio of males to females. The temperature range over which this changes is just a few °C, hence the depth of the nest is critical. This is called the ‘transitional range of temperatures’ (TRT) and covers a complete sex ratio change from 100% male to 100% female. The lower end of this scale being all male and vica-versa at the top end (see ‘The Biology of Sea Turtles Volume II’).
Unfortunately with global warming this means that the proportion of females to males is increasing and is yet another example of the horrendous pressures facing the future of turtles worldwide.
Back on the beach, our beautiful female lays a total of 85 eggs. We carefully remove them as she lays and store them in a plastic bag. This removal is essential because unfortunately poaching is rife along this part of the coastline. During the high season up to 120 turtles may come ashore every night and even with 2 patrols looking for nests over a 30km stretch 20% of nests are still raided and the eggs removed. They will end up as a delicacy on some persons’ plate!
Each turtle may nest between 1 and 3 times in a season and return every year, so even with the huge losses hopefully some of her hatchlings will make it to the sea, and possibly one day one or more of them will make it back to this beach, although the odds are heavily stacked against them.
The eggs are about the size of ping pong balls, warm and slightly soft. They seem vulnerable to damage, but thankfully, they are not, and can last up to 24 hours in the bag. We also made sure to add some of the sand with the natural antibiotic to ensure the highest chance of survival for the eggs and hatchlings. Even with the best care to build nests by the mother or the conservation group survival rates at this stage of their lives are only 60% – 80%, and this is the easy time!!
The next morning we took the eggs to a nesting site at a place called Tortugario. This is a turtle zoo and educational centre just 3km from the conservation camp where volunteers from ‘Projects Abroad’ go to help with general running of the zoo. Pablo, one of the main guys on the conservation project, took me to meet the site director Maria. He also kindly translated as my Spanish is terrible!
Maria was fantastic and so helpful, she spent time explaining her point of view. She believes this site is set up to help educate people young and old about turtles, crocodiles and mangroves. She thinks that keeping a few turtles in tanks is a small sacrifice to pay if the general public learn to love and hopefully respect turtles in the long term. Her team also visit schools to teach children as young as 5 – 6 years about their work and other important environmental issues.
Tortugario is one of only 2 zoos built in Mexico specifically for turtles and the only one that includes egg collection and a nesting site, however there are 127 other sites along the coast that collect eggs and raise them to hatchling stage. Maria has been running this Government built institution for 25 years and it has been a difficult challenge with so many financial and social factors affecting what she can achieve. However it is estimated that her centre has helped to collect, rear and release around 1.5 million hatchlings. That is quite an achievement in difficult circumstances.
After my conversation with Maria we entered the nesting site but were greeted with the sad sight of many eaten eggs strewn around the sand. A coati (Nasua nasua) had managed to find a way in, this is a racoon like animal with the cunning of a fox and a healthy appetite for eggs. Thankfully it had only destroyed one nest. Just one more of the challenges facing the survival of the Olive Ridley species.
Our next job was to simulate the actions of the female Olive Ridley turtle and dig a hole to the same depth as the turtle ie 45cm and with a bulb shape at the bottom. Once completed we carefully placed the eggs into the hole making sure to add the sand with the antibiotic. We then gently filled the hole with damp sand at first then dry sand on top. Job done. All going well, in 45 days time a whole batch of hatchlings will fight their way to the surface.
We marked the site, then checked the other nests. Many of the hatchlings had already reached the surface and been released so our next job was to clean several older nests. We carefully removed the sand and found a combination of empty eggs, dead rotting turtles, and broken eggs teeming with maggots. This is not a job for the faint hearted! However to our delight we also found 22 hatchlings. We completed the nest clean, then took the hatchlings for release into the Pacific Ocean.
It is recommended that the hatchlings are released 8 metres from the uppermost reach of the waves so that the females imprint on the beach for return in 10 to 18 years when the turtles reach maturity.
We carefully placed the little rascals on the sand and stood back to keep a close eye on their progress. They are so small and vulnerable and there are predators lurking at every turn. Crabs and birds take many thousands of hatchlings from the beach, it seems so cruel that they are so close to their natural environment and just fail to reach it.
Dangerous predators lurk at every turn, this is the land crab (Cardisoma spp.) which grabs hatchlings but ghost crabs (ocypode spp.) are the biggest danger.
Once they reach the water’s edge some are constantly driven back by the waves, they fight and fight to enter the sea and eventually all 22 are gone. Their determination to survive is awesome and now their real journey begins, we can only imagine what dangers await them in the ocean. Good luck you little beauties!
What an experience.