Ascension Turtle Tours

On the 2nd February we held our first official Turtle Tour, Abi was acting as spotter and was out on the beach looking for turtles at suitable stages (digging and laying) for us to take visitors to see the laying process. I was leading the tour and Anna was assisting me with the group of people and then also in between us and helping Abi once we were all at the beach. 

For our first tour we were fully booked; 12 people, although a couple didn’t turn up. The tours start at the conservation office at 21:00 where we give short briefing, hand out red torches, and play a short video on sea turtles on Ascension before heading down to long beach to see the turtles. 

Here is an example of the information we give about the turtles on Ascension/some of my notes: 

General Turtle Info: 

The seven species of sea turtle are descendants of small species that wandered out of freshwater marshes and entered the sea. Turtles moved into and out of the oceans several times beginning in the Jurassic period and into the Cretaceous, with modern turtles evolving about 110 million years ago. 

Ascension turtles 

Green turtles are a big part of Ascension history, and ascension is a hugely important nesting area for green turtles, as the second largest rookery in the Atlantic behind Tortuguero in Costa Rica. 

Ascension was discovered in 1501 and until the early twentieth century turtles here were important as they were harvested for meat – records show ships took them alive as far as Europe as they were considered a delicacy. Unfortunately, this greatly reduced the population of green turtles seen around Ascension and due to many other threats across the globe green turtles are listed as endangered on the IUCN red list. However, monitoring began here in 1977 and conservation efforts since have led to nests laid on ascension have increased by 6 times since, from just under 4,000 to 24,000 nests per year with 50,000 nests recorded in 2017. Population size in 1822 was thought to be 17,600 and is now thought to be above 14,000 individuals annually. 

Ascension turtles are also the largest of their species being up to 1.5m and up to 250kg to help them cope with the long journey to Ascension from their feeding grounds. Sea turtles exhibit a behaviour called natal homing, which means they return to the same beach they were born on (or as close too as they can) to nest. 

Green turtles of Ascension travel over 2000km for around six weeks at around 5mph all the way from their feeding grounds in Brazil and will stay here for around 4 months before making the same journey back. Both males and females make this migration which begins in October, males do this annually and females do this at intervals of around 2-3 years due to the energy required to produce eggs and go through the nesting cycle so need time to build up fat reserves. Whilst they are here, they will also fast and will not each for the full 6+ months. Once they reach the island the females will mate with various males from November to January and store the sperm to fertilise eggs later which means there can be multiple paternities within one clutch. 

They are thought to navigate using capabilities to detect the magnetic signatures and angle and intensity of the earth’s magnetic field – and it is also thought hatchlings imprint using internal compasses. However, the magnetic signature of Ascension can alter by around 60km between nesting periods and so other cues are also thought to be used. For example, turtles can smell by pumping water through their nose and an experiment on Ascension showed that smell might also be important. They took 6 turtles from ascension and released 3 of them downwind and 3 upwind and those released upwind swam in circles before returning to Brazil and those released downwind made it back to Ascension. We see the first nests being laid around December with the peak in March and ends around June. 

Males can be identified from females by their large tails and large claws on their front flippers, they use the front claws to hold onto the front of the female’s carapace and use their long tails to hook under the female to transfer sperm and mate with females. After a few weeks the females will come onto the beaches to lay their eggs, this happens at night-time so that it is cooler, and the moon can act as a guide. Once the turtle begins ascending the beach, she will go through a series of processes to complete a successful nesting attempt. 

First they begin by testing the sand and will use their four flippers to flick sand in a stage called body pitting which will allow her to lower herself in the sand a create a body pit or ‘turtle hole’ if she is satisfied with her location, the temperature and texture she will then begin to dig her egg chamber using only her hind flippers which alternate in delicately scooping sand out, she will also reach into the chamber feeling the sides to gauge the depth until she is happy. This process can take around 20minutes to an hour depending on the turtle and can also be abandoned at any point and started again multiple times. The egg chambers are usually around 1 metre deep and 70cm from the top once the eggs are laid. Once the chamber is dug the female will begin twitching her tail and watery secretions which lubricate eggs and keep them moist until covered will begin to drop from her cloaca. This will help to prevent bacterial and fungal infections within the nest. Slow contractions begin and she will lay approximately 120 eggs depending on the size of the female, which are the size of Ping-Pong balls, with 1 to 4 eggs being laid with each contraction. The eggshells are soft to stop them breaking as they fall into the chamber. The laying process can take 20 – 40 minutes and whilst she is laying, she enters a trance like state due to a hormone called oxytocin which acts as a pain reliever. This is the stage we will be observing today as we are least likely to cause disturbance to the turtle during this stage. 

Once her eggs are laid, she will begin covering the egg chamber with her hind flippers where she will push sand in over the top of the eggs conserving air spaces for oxygen to diffuse through the permeable membranes of the eggshell to developing embryos, this covering process takes around 10 minutes before she enters the last stage before returning to sea which is camouflaging. This can be easily confused with body pitting but is where the females use mostly their front flippers to flick large amounts of sand backwards and over the chamber forming a long sand spray which can hide the chamber and protect the nest from predation (although this isn’t a huge problem on ascension) but can also help protect the eggs from being dug up by other females. The camouflaging process can take anywhere up to 4 hours to be completed. 

The eggs take approximately 50-65 days to incubate with the average for long beach being 54 days. So, we will probably start seeing hatchlings around April all the way until August time. It is thought that only 1 in 1,000 hatchlings make it to adulthood, but any females that do will return to Ascension when they are approximately 25-30 years old and will continue nesting throughout their whole life which can be over 80 years. As we said, females do not nest every year but research in 2012 on ascension revealed that turtles can lay approximately 6 clutches in a season with some nesting up to 10 times with intervals of 10-17 weeks in between. 

Other threats sea turtles are currently facing globally include entanglement from ghost nests and disguarded fishing gear, climate change, beach redevelopment, tourism/overcrowding beaches, light pollution, oil spills etc. When with a laying turtle, Point out: Scute patterns, Mating scars, salt tears/salt ducts, Average Sizes For fertilisation yolky follicles are released in batches which are fertilised in her oviducts and then the yolk enlarges and albumin coating then shell develops before laying. She has a predetermined number of eggs she can lay in a season, and this depends on nutrients available to her at the beginning of the season. 

Approximately 14 days between each clutch being fertilised and develop into shelled egg – during this time she rests on the seabed to conserve energy. As development proceeds the chorion and allantois fuse to form the chorioallantois membrane which facilitates embryonic breathing. The eggshell is thin and porous enough to allow gases to pass through – and so the embryo breathes through the shell Sea turtles also exhibit something called temperature dependent sex determination in which gonad development is affected by external environmental conditions during a thermosensitive period (TSP). For sea turtles this is the middle third of development with conditions below 28 degrees producing clutches of 100% males, and temperatures of above 30 degrees producing 100% females, and the middle producing both males and females. With climate change there is a concern of increasing feminisation. 

Here on Ascension, we are currently deploying 5 temperature loggers per beach per month to record nest temperatures to predict sex ratios for ongoing monitoring efforts. On Long beach the sex ratio is predicted to be about 70% female on long beach, compared to almost 100% on Northeast Bay.

Hatching 

After the eggshell is pierced by the egg tooth the rest of the yolk is absorbed (provides energy for two weeks) until the plastron straightens out and hatchling may wait up to 48hours before making their way up the chamber 

Hatchlings use primarily visual cues to find the sea but do use the sound of the surf Hatchlings loose up to 20% of their body mass to evaporative water loss during journey out of the nest, across the beach and frantic swimming and so drink sea water- over next two days then filter out the salt using salt glands behind their eyes that excrete salt as tears 

Navigation

 Sea turtles brains contain magnetite (iron compound) which help sense the earth’s magnetic field as the magnetite is drawn to north pole which helps detect direction of travel 

Surge of testosterone signals for migration back to mating areas and nesting beaches 

May follow magnetic navigation, celestial cues, chemical concentrations and memory of landmarks but not really known Male turtles begin migration before females to await female’s arrivals at mating grounds

Mating Females are only receptive to mating a month before nesting season and the 12 hours after laying each clutch of eggs 

Biology 

Turtles have a three chambered heart, two lungs, a lobed liver, stomach, digestive system, arteries, veins and have high body temperature but lower metabolic rate – warm but not warm blooded 

Sea turtle’s oesophagus is adapted to eliminate salt water taken in with food – when eats contracts muscles so excess water is expelled out of the mouth – lining the oesophagus are cone shaped structures called papillae which are connective tissue covered with keratin and point towards the stomach to keep food in place. 

Turtles’ kidneys are unable to concentrate urine sufficiently to remove excess salt so they evolved the salt gland behind the eye modified tear duct. 

Turtles can remain underwater active for 45 minutes without breathing but as they rest they spend more time submerged and can sleep through the night. 

Turtles are protected from the bends as they do not have extensive blood vessels around their lungs as their air passages are reinforced with cartilage and surrounded by smooth muscles which help them to quickly empty and refill lungs. 

Sea turtles have good vision underwater but on land are near sighted because their lenses are adjusted for refraction caused by water 

Sea turtles only have one ear bone called the columella and do not have an external ear – their eardrum is a continuation of the skin on the skull and sea turtles can only hear low frequency sounds and not very well on land but can sense vibrations 

A sea turtle can smell under water by pumping water in and out of its nose but it is not known if they can smell through air