Each turtle tagged has a uniquely coded number
One of the most elusive and mysterious creatures in terms of their movements is the sea turtle. Long before they became scientifically interesting, they were of interest as a key food source, particularly females that come on land to lay their eggs. Over time turtle populations declined and the important role they play in the ocean food web became more apparent.
The food web is a fine balance between plant and animal species, and when this balance is altered it can have an effect on the whole ecosystem. The Hawksbill turtle feeds on sponges, a coral reef species. By eating the sponge they ensure that the fast growing sponge does not take up too much space on the reef, allowing for corals to grow. Corals are the base of food and nutrient flow on a reef and it is very important that they have space to grow and colonise.
Hawksbill turtle monitoring on Cousin Island
It became important to understand marine turtle habits, movements and behavior. But how do you learn about sea turtles biology when they spend all their time underwater? One of the best inventions for marking and identifying individual animals is tagging. Birds are tagged using a ring that is placed on their leg, sheep are tagged by painting a number on them, cows are tagged on with a ring on their ear and marine turtles are tagged using a metal tag that is attached to their front flipper.
The first tag to be applied to turtles in Seychelles was in 1973 on Cousin Island Special Reserve. Thereafter, turtle tagging was done on Curieuse, St Anne, Aride, Cousine and Denis islands.
Hawksbill turtle nesting on Cousin Island, Photo by Henna Tanskanen
Tags are useful in providing information about female turtles’ nesting habits. With Hawksbill turtles now critically endangered it has become very important to know where they go outside of the nesting season so as to extend protection to these locations, in the hope of better conserving the species. But to date none of the metal tag numbers have been recovered from turtles outside the region from which they were tagged.
Scientist now use satellite tagging. This method is much more expensive and therefore was trialed on just five Hawkbills from Cousin Island Special Reserve in 1998. The aim was to see where the turtles went after nesting in order to find out the key foraging areas for this species. The experiment worked and the results showed that none of the five turtles traveled beyond the edges of the Seychelles bank, and none moved further than 175 km from the nesting beach.
Earlier this year Mervin Bick, an ex-warden from Cousin was working on a boat travelling near the edge of the Seychelles Plateau. He spotted a Hawksbill turtle that had a shiny tag on it, same as those he had seen and used on Cousin Island. Mervin got close to the turtle and record the number on the tag. Mervin worked with Nature Seychelles on Cousin Island where part of his job was to learn and participate in the turtle monitoring program. When he returned to Mahe he passed this information to Nature Seychelles head office team who were able to look up the tag and track where it was issued.
This turtle was first tagged on Cousin Island on 18th November 2011 where she nested at least 3 times. The location where Mervin observed her was approximately 208km South East of Cousin Island. This record is the first of its kind and is congruent with the satellite study which shows that Hawksbills key foraging habitat is indeed within the Seychelles region. These turtles are truly Seychellois and deserve to live free helping to protect the coral reefs within the region that are so vital to the Seychelles economy.