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My PhD with the sea turtles from the Bijagós Archipelago, Guinea-Bissau – Part I, the Hawksbill

I am Fernando Madeira, a PhD student of the doctoral program BIODIV cE3c at the Faculty of Sciences of the University of Lisbon (FCUL). I research different aspects of marine turtle ecology and conservation at the Bijagós archipelago, such as their diet and feeding areas, status of the breeding population and behavior patterns.

My PhD fits within the MAVA Foundation funded project; ‘Consolidation of Sea Turtle Conservation in the Bijagós, Guinea-Bissau’, and it is a collaboration between FCUL, MARE – ISPA, Instituto Universitário, University of Exeter, and the national protected areas authority, the IBAP.

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Me, with a juvenile green turtle

In the past two years I have been conducting fieldwork at the Bijagós, mainly at the small island of Poilão. Here, the IBAP has set a small base camp, where a team, composed of local collaborators, IBAP technicians and international researchers, is settled during the nesting season for marine turtles (June to November). Most of my work is directed towards green turtles (Chelonia mydas), the most abundant species in the archipelago, but I am also studying the small nesting population of the critically endangered Hawksbill turtle (Eretmochelys imbricata).

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Hawksbill sea turtle
Hawksbills are one of the most sought-after sea turtles by poachers, as, in addition to being poached by its meat and eggs, like other marine turtles, their thick shell scales, or scutes, are coveted to produce artisanal crafts. Their mottled pattern contrasting with a translucent matrix creates a beautiful effect when polished, and it is used to make combs, bracelets, eyeglass frames, among many other luxury items.

At Poilão, in contrast to the green turtles that lay thousands of clutches annually, the average number of hawksbill sightings is about six each season. Studies on the East Atlantic Hawksbills are very scarce, and this is the first time that this species is being studied at Guinea-Bissau. My aim is to assess the size of the breeding population and its nesting history, to identify foraging areas, and to check the status of this breeding stock through genetic analysis.

So far, I recorded all hawksbill nesting events during the 2018 and 2019 nesting seasons, gathered genetic samples, protected all clutches found and deployed four GPS tags to identify important foraging areas. In total, I identified eight different females and their respective nests. Some of these turtles have been nesting at Poilão for at least 11 years!

Nesting hawksbills are followed very closely, and there are so few of them among so many greens that each encounter is always a celebration! When we find one we keep our distance, to minimize stress and ensure that all eggs are laid safely. We wait until the turtle finishes laying or is returning to the sea to gather data. Afterwards, we transfer the clutch to a hatchery at the base camp, making sure it will not be predated or dug up by one of the many green turtles.

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Translocating hawksbill turtle clucth to hatchery

I end up spending a lot of time with each turtle and its clutches, and since they are so few, anytime I reencounter one of them it is like finding an old friend amongst a crowd (of green turtles). Each one has its peculiarities, like different favorite nesting spots, inquisitive nature or innate ‘bitey-ness’, which really gives them individuality.

Thanks to the GPS data, we have found that these turtles seem to migrate to a common foraging area, situated within the Bijagós archipelago. We also have found some potential hawksbill x green hybrid clutches, suggesting that there maybe a lack of males in this breeding population.

I feel really privileged to have such close contact with these turtles and I hope to, not only to shed some light in a poorly known population, but to also make a difference in its conservation!


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