Projects - Sea Turtle Satellite Project

Introduction

In collaboration with the Dutch Caribbean Nature Alliance (DCNA) and the Nature Foundation Sint Maarten, STENAPA has initiated a satellite tracking study of its nesting green and hawksbill turtles. To date, information is scarce about where these animals go once they leave Statia; this project aims to track the turtles as they migrate from the nesting beach to their foraging grounds, as it is known that they do not stay around Statia once the nesting season ends. Learning their movement patterns at different phases of the life cycle gives us a clearer picture of their geographical range and so allows us to improve protection and conservation efforts, not just on the nesting beaches, but also in other essential habitats.

Satellite attachment

Under the supervision of Dr Robert Van Dam, a sea turtle biologist with many years of experience using satellite telemetry to track turtles, transmitters were attached to three females on Zeelandia Beach (the main nesting beach on the island). The attachment process begins only when the turtle has finished laying her eggs and covered the nest site with sand. To limit her movements while the transmitter is attached she is placed in a holding box. First, her carapace is cleaned of any algae or barnacles.

Next, the transmitter is positioned on her back; it sits towards her head so that when she surfaces to breathe the device clears the water and can send a signal to orbiting satellites. It doesn’t sit directly on the shell but has a soft cushioning layer underneath, which also prevents it moving while several layers of fiberglass are laid over the top. These set hard creating a barrier that protects the transmitter from the everyday wear and tear it will receive during the next few months at sea. Once the fiberglass dries, which takes about an hour, the turtle is released.

As she travels we track her progress on-line; location data are received from the satellites and a map showing her route is updated every 24 hours. It is hoped that the transmitter will keep working at least until she reaches her feeding ground, which may take a couple of months. Eventually it will stop sending signals, either due to battery failure or that is has been knocked off the turtle as she moves around reefs or other underwater obstacles.

“Miss Shellie” – August 2005

Miss Shellie was a green turtle that was first encountered while nesting on Zeelandia Beach on 30 August 2005. She was given two metal identification tags in her front flippers and also measured; she was large for a green, her carapace was 113.2cm long and 103.5cm wide. She nested twice between the first sighting in August and 20 September, when she had the satellite transmitter attached. She returned to lay a final nest ten days later, on 1 October.

Surprisingly, even after she had finished nesting for the season she did not migrate away from Statia waters; signals from the transmitter showed that she remained offshore from Zeelandia Beach for the majority of the six week period during which her movements were followed. Several times she rounded the northern end of the island, but never travelled more than 5km from the release site.

Most of the signals indicated that she was within the boundary of Statia Marine Park, in water with a maximum depth around 30m/100ft. It was unusual that she did not migrate to a feeding ground elsewhere in the Caribbean for it is generally assumed that adult turtles have separate feeding and nesting areas. Her movements suggest that she had found a suitable foraging ground close to her nesting beach. Typically green turtles feed on sea grasses which can only thrive in relatively shallow water; the fact that she was almost exclusively in shallow water suggests that she had probably located a sea grass bed in this area and so had no need to migrate to a distant feeding ground. The final transmission was received from Miss Shellie on 15 November, 2005.

Her name was chosen by Krystell Statie, age 12, from the Statia Terminal School, St Eustatius. She was one of the winners of an art, craft and writing competition organised for schools as part of the community awareness programme associated with the tracking project. Depending on their age, students were asked to either draw a picture of a turtle, write a story about what a turtle might experience on its migration, or create a turtle model out of recycled materials; Krystell was the winner of the model category, and received several prizes and the chance to name one of the tracked turtles.

Map showing the most accurate location points received from “Miss Shellie” in 2005 – green dot shows the release site on Zeelandia Beach

“Lisa” – September 2006

This was the first hawksbill turtle to have been encountered during night patrols since 2004; two hawksbill nests were observed in 2005, and several tracks had been recorded already during the 2006 season, but no females had been seen or tagged. The turtle was intercepted on her way back to the sea at around 1.00am on 7 September, 2006. She had obviously not nested when initially seen as researchers checked her for tags and she then crawled back up the beach and nested in the vegetation close to some large boulders at the very northern end of Zeelandia Beach. She laid 143 eggs; a small temperature recorder was placed in the nest to monitor the temperature each hour during incubation. This data will help determine the percentage of male and female hatchlings in the nest, as their sex is determined by the temperature at which they incubate not by chromosomes, and is part of a larger study being conducted by a marine biologist in Florida.

The name given to this turtle was “Lisa”, chosen by the second of the competition winners from 2005, Evan Hassell, Class 3, Governor de Graff School. He won the drawing category of the contest for his picture of an underwater scene depicting a turtle in the water around St Eustatius.

“Lisa” was medium size for a hawksbill turtle, her carapace measured 85.5cm; however, she was extremely strong and gave the research team quite a hard time once they had her in the holding box. The box had been designed for the dimensions of a green turtle, which are larger than hawksbills, and so it meant that she had too much space and so was able to turn around very easily, which made the transmitter attachment procedure a lot more difficult! Due to a slight problem with the fiberglass resin taking too long to dry, “Lisa” was released as the sun was rising, which gave everyone a unique opportunity to see a turtle in the daylight and not under red lights in the dark, which is how they are normally seen during patrols.

‘Lisa’ travelled first to St Barts, and then spent time around Anguilla before swimming to St Croix. She remained there for nine days, and we assumed that she had reached her feeding ground; a coral reef area where she could find her favourite food items, sponges. But we were wrong it seems! On the 12 October she was on the move again; heading back towards Anguilla!! The latest information from the transmitter, which is still sending signals each time she surfaces to breathe, indicates that she is just to the west of Anguilla. Since her release on the 8 September she has travelled over 1,000km on an amazing journey that has taken her to several different islands in the region. We don’t want to say that Anguilla is the end of her travels, for who knows where she may go next?? All we do know for sure is that she has us a little confused about where her ‘final’ foraging area is, to say the least! See the map below for the latest position.

Grace – September 2006

“Grace” is an endangered green turtle, who nested on 17 September at Zeelandia Beach, on the Atlantic side of St Eustatius. Just like the hawksbill turtle “Lisa” that had a transmitter fitted on 7 September, this female nested successfully before researchers fixed the small tracking device to her carapace (shell); she laid 129 ping-pong-ball sized eggs! This turtle was quite a lot larger than the hawksbill female, measuring 106cm in length; however she was much calmer throughout the 2-hour long attachment procedure, making it a lot easier for the team to get the transmitter fitted properly. Fortunately they were able to release her back to the sea just before a huge rain storm began; this rain, if it had started while they were working with the transmitter, would have severely hampered the entire attachment process.

By mid November 2006, it seemed that the green turtle named ‘Grace’ has indeed already found her foraging ground. Since her return to the nesting beach at the end of September, which was presumably her last for the season, she has travelled to the southern end of St Kitts, and has remained there ever since! Her latest location signal was from the channel between St Kitts and Nevis. When we checked what was there we found that it appears to be relatively shallow bays; such an area would provide suitable conditions for sea grasses, her main diet item. She has swum over 1600 kilometres in total, travelling between St Eustatius and St Kitts, though at present she is just 50km straight-line distance from her release site.