On July 4th we joined a number of other cruisers for a trip with Jesse James, of ‘Members Only’ Maxi Taxi Service fame, for a night-time visit to the shore near the village of Matura, in the northeast corner of Trinidad. There, we joined locals and tourists gathered to observe a remarkable sight: leatherback turtles lumbering up onto a soft sandy shore to lay their eggs.
Leatherback turtles are the largest turtles in the world; they can weigh up to a ton, and they can dive to depths of 4,200 feet—deeper than any other turtle—and can stay down for up to 85 minutes. They are unlike other turtles in several respects the result of which is their deep-diving ability: They can maintain their body temperature as much as 18 degrees Celsius above the cold, deep waters where they feed, and their carapace is not a hard shell, but is rather a spongy material covered with, um, well, ‘leather’. The lack of a rigid breastbone allows it to collapse during deep dives, putting pressure on the lungs. And the large amount of oil in the skin and the leathery shell absorbs nitrogen, reducing problems arising from decompression during deep dives and resurfacing. (You may at some point have seen a picture of someone standing on a turtle as though it were a surfboard. Never do that to a leatherback: the soft shell will collapse and puncture its lungs and in a few hours it will die from a hemorrhage.)
Leatherbacks are an ancient species; they were once contemporaries of the dinosaurs, and they are currently listed as endangered. There was a time when the poaching of turtles and their eggs was a major problem on the beaches of Trinidad, but no more. In 1990 Nature Seekers was established as a non-profit organization with the aim of protecting nesting Leatherback turtles in Matura. It is the oldest turtle conservation group operating in Trinidad & Tobago. Today, Nature Seekers participates not only in beach patrols but also in data collection and tagging of sea turtles, and also provides tour services to visitors, including trips to nesting beaches such as the one we experienced.
After all visitors had arrived, we first heard a general discussion of what we would see and what rules we should follow: Red lights only while traversing the beach, and kept pointed straight down. No flash photography until given the okay by the tour guide, who would wait until the turtle had begun actually laying eggs before giving permission, since the turtle enters a trance while laying, a trance so deep as to permit volunteers to measure and tag and allow visitors to gently touch and photographers to use flash. At the conclusion of the orientation, we broke up into small groups of about ten with each group assigned its own guide.
Leatherbacks live in the open seas around the world. In the Atlantic Ocean their range spans across the entire region, as far north as the North Sea and as far south as the Cape of Good Hope. Unlike that of other sea turtles, feeding areas for leatherbacks are in colder waters, where there is an abundance of their jellyfish prey, which broadens their range. However, only a few beaches on both sides of the Atlantic provide nesting sites; they return to the tropics in order to mate and lay their eggs. Trinidad is especially popular, with more than 2,000 turtles coming each summer to Matura, the most popular of the nesting beaches in Trinidad, with a shore of nice soft sand that runs for about five miles.
It is an incredible sight to see such a massive creature laboriously pulling herself out of the sea and up onto the sand just above the high water mark of the recent tides. She digs herself a shallow pit with her flippers, scraping off the top layer of sand, and then settles for a bit, testing the temperature and moisture content of the underlying sand. If satisfied, she uses her rear flippers to dig a hole, using first one flipper and then the other. The precision of the dig is mindboggling. If the right fin is doing the digging, it moves through the bottom of the pit like a spoon scooping from left to right, and then, retaining the spoon shape, she lifts the fin carefully out of the hole and flips its contents to the right. She then places that fin down flat on the shoulder of the hole in order to prevent sand from re-entering. When the left fin has done the same in a mirrored effort, the right fin first flips out to the right to clear any sand that might have rolled down into the hole and then, ever so carefully, lifts up high to swing to the middle of the hole to descend for another scoop. When the hole is finished, its shape is that of an inverted light bulb: straight down for a bit and then flaring out at the bottom.
Then she begins laying her eggs: anywhere from 80 to 120, with about 85% viable, although a few are small and are thought to be useful for providing cushioning and extra sustenance for the hatchlings that will appear in about 60 days. Why extra sustenance? Because a hatchling that breaks out of the membranous ‘shell’ will not emerge from the sand if the sand is too warm; warmth indicates sunlight and that indicates extra vulnerability to natural predators like crabs, birds and mongooses. It’s best to wait for the cover of darkness.
What if the weather is cool and rainy? Then the hatchlings will emerge if ready, and it may be feast time for the predators.
How do the hatchlings at the bottom of the heap manage to climb out? They pull themselves up past the hatchlings above them, so hatching is kind of a “first in – first out” discipline.
Tagging has revealed that adults are prone to long-distance migration, which occurs between the cold waters where mature leatherbacks feed, to the tropical and subtropical beaches in the regions where they hatched. In the Atlantic, females tagged in French Guiana, for example, have been recaptured on the other side of the ocean in Morocco and Spain.
Mating takes place at sea adjacent to the nesting areas. Males never leave the water once they enter it, unlike females which nest on land. After encountering a female (who possibly exudes a pheromone to signal her reproductive status), the male uses head movements, nuzzling, biting, or flipper movements to determine her receptiveness. Females mate every two to three years. Fertilization is internal, and multiple males usually mate with a single female. One female may lay as many as nine clutches in one breeding season, with about nine days between nesting events. After laying her eggs the female carefully back-fills the nest and then packs it down a bit by using her body, she then disguises it from predators with a scattering of sand.
The temperature of the nest determines a hatchling’s gender. Warmer temperatures produce mostly females, and cooler temperatures produce a majority of males. There is a pivotal temperature that produces an equal ratio of males and females. While other sea turtle species almost always return to their hatching beach, leatherbacks may choose another beach within the region. They nest at night when the risk of predation is lowest. Since leatherback turtles spend the vast majority of their lives in the ocean, their eyes are not well adapted to night vision on land. The typical nesting environment includes a dark forested area adjacent to the beach; the contrast between this dark forest and the brighter, moonlit ocean provides directionality for the females who often nest facing towards the dark and then return to the ocean and the light.
On the night of our visit we walked a considerable distance to the south along the beach from the entrance point, stumbling along in the soft and uneven sand. Finally, our guide received a message on his radio that there was a turtle on the beach ahead of us. When we arrived, we stayed well back and watched it settle in. She had dug for perhaps 45 minutes when our guide said that he knew she would soon abandon the effort: she had reached water and that was causing the hole to repeatedly cave in. So we moved on, giving her privacy for her laborious trip back to the sea. Soon, we encountered another turtle, and this one was experienced: she had two tags on her rear fins and she expertly and efficiently dug her hole, exhibiting the behavior I described above. When she began laying her eggs, we were given permission to use flash and to gently touch her. Our guide pointed out that as she deposited, she shielded the hole with one of her rear fins in order to prevent predation of the new eggs. We left when she finished laying the eggs and covering the hole and camouflaging the area. As she laboriously began to drag herself back to the sea, it was clear that she was exhausted. We were tired too – it had been a long night. But it was also clear that we human observers all felt a sense of wonderment and awe at such an elaborate and fantastic demonstration of the beauty and power of nature.
An avid amateur photographer and naturalist, Charles (Chuck) Shipley was a Professor of Computer Science until his retirement in 2005, when he and his wife Barbara moved aboard their Kadey-Krogen 48 North Sea TusenTakk II. They have been cruising the Caribbean since January 2007.