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Egg Translocation & Nest Implantation - A Green Turtle Release Programme

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Egg Translocation & Nest Implantation - A Green Turtle Release Programme
07Jun 2019

Our animal team carefully implant the eggs on the wild beach

Cayman Turtle Centre’s core mission is to conserve sea turtles, and a part of our conservation efforts includes taking captive bred turtles, and releasing them into the wild.

So far we have released more than 32,000 turtles into the waters around the Cayman Islands, a combination of hatchlings and “head-started” turtles a year or more in age. A recent DNA analysis study by the Department of Environment and the Universities of Barcelona and Exeter, funded by the UK’s Darwin Plus initiative, established that many of these have come home to the Cayman Islands to nest. Essentially, what they found was great news, a resounding confirmation of the success of our release programs. They determined that 9 out of 10 nesting green female turtles were related to those released during the 1980s and 1990s from the Turtle Farm, as we were called back in those days. They also discovered that green turtle nest numbers in Grand Cayman each year have risen from just one nest recorded twenty years ago in 1999, to well over two hundred in 2017. 

One of our green turtle release programmes is quite unique, called egg translocation and nest implantation. It is a way of introducing captive-bred green turtle eggs into the wild, by replicating, as carefully as possible, a real-life green sea turtle nest on the beaches of Grand Cayman. The eggs are laid on our ‘beach’ at the side of the Breeding Pond at our Centre, a sea-water lagoon where all of our big breeding turtles live. These eggs have been carefully collected from our beach on the night they were laid, placed in an incubation box, and then incubated for nearly two months in our Hatchery. At this stage the eggs are within just a few days of hatching. We bring those eggs to a specially selected Grand Cayman beach to be placed, one by one, in the nest we create in the sand.

The nesting beach at the Cayman Turtle Centre

The nesting beach at the Cayman Turtle Centre

The actual number of eggs implanted in the nest varies, but typically half of the eggs from a clutch that was laid in a nest at the Cayman Turtle Centre are translocated to the implanted Grand Cayman beach nest. We keep the other half of the clutch, their siblings, under observation in our Hatchery at the Centre. This is our control group, intended to give us a better idea as to the approximate timing of their hatching out of their shells and eventual emergence from the sand.

Control box in the Centre's Hatchery

Control box in the Centre’s Hatchery showing the progression of the hatching and gives us insight into the approximate timing for the hatch out of the nest implanted on the wild beach

Great care is taken in creating the nest on the wild beach and moving the eggs from the Centre. In studying the nests built by female green turtles at the Centre and in reviewing published research, we have an understanding of the depth and width needed to dig the near perfect egg chamber on the beach. The eggs are kept upright – in the same orientation as they were when they were laid to aid in the translocation process. Turtle eggs are sensitive to sand moisture levels. Therefore care is taken to pack eggs in sand of optimal moisture levels, the hole is filled with sand all the way up to the level of the beach, and we place protective markers around the nest. We monitor the nest each night starting from the anticipated hatch date until the little hatchlings slowly make their way to the sand surface and are ready to come out.

Protective markers are placed around the nest

Protective markers are placed around the nest

The hatchlings while still in the shell develop a sharp egg tooth at the tip of their beaks. They use that to puncture their leathery egg shell and their little fins join in to tear open the shell and push the shell away behind them. Once they hatch out, the hatchlings will take another roughly 7 to 10 days to climb up through the sand from the bottom of their nest to the top of the sand. Before you see the little turtles emerging, sometimes they will wait together, just beneath the sand surface, till what they instinctively decide is the “perfect” moment one night when they will emerge as a group. By instinct, they typically wait till dark to appear, reducing the chances of being seen by predators. Eventually one hatchling will take that chance to push its little head up to where it can peek out, maybe a little hesitant and on instinct not wanting to go out alone due to the risks of predators. Other hatchling heads may become visible too. Then eventually one will move to pull itself out of the sand, the others sense it, and then they all scurry to get out.

Turtle hatchling poking its head out of the sand

At night we use red filtered light to reduce interference with the emergence. Here is a turtle hatchling poking its head out of the sand

Within a few minutes of each other, most of the hatchlings crawl out onto the sand surface – this event is called the “mass emergence”. I mean who wants to be last as there is protection in numbers from crabs and birds lying in wait for an easy meal! From there they will quickly run down to the surf pushing with their fins and sliding over the sand on their flat little bellies, seeking the cover of water. However, it is not uncommon to see either one or a few hatchlings emerging a day or more before the “mass emergence”, to make the journey on their own.

Mass emergence where most of the turtle hatchlings crawl out of the sand’s surface

Mass emergence where most of the turtle hatchlings crawl out of the sand’s surface

When the turtle hatchlings senses a wave reaching them, they will let it sweep them out into the surf – causing what is called a “frenzy swim” for 24 hours or more heading straight into the oncoming waves so as to get as far offshore as quickly as possible until the encounter a mat of floating sargassum seaweed which will be their habitat for the first few years of their lives.

Before leaving the beach, the hatchlings have imprinted key factors of the location of that exact beach. The imprinting relates to characteristics of the earth’s magnetic field at that point, from which they store a permanent memory - similar to a latitude and longitude in a process called “geomagnetic imprinting”. They have sensor cells in their brain with ferrous compounds in them, that can sense magnetic fields.

It takes upwards of twenty years for a green turtle in the wild to become old enough to reproduce.

Using those stored coordinates, turtles can navigate hundreds or sometimes even thousands of miles of ocean, and then, decades later, come back to the same beach that they left as hatchlings. That is one of the reasons why the nest translocation program is important because by replicating a ‘natural’ nest, it is believed that the imprinting process will help to guide them back to this beach to mate just offshore and to nest on it.