Four species of marine turtles come ashore to lay their eggs on Bioko Island's southern beaches from November to February:
Binomial: Dermochelys coriacea
Largest sea turtle, with a shell length of 52-70 inches and a mass of 550-2000 lbs. Carapace is black with white splotches, plastron is white with black splotches. Carapace is a layer of rubbery skin instead of a hard shell, and is raised into seven longitudinal ridges. Range includes all ocean habitats except the Arctic and Antarctic; Africa’s Gulf of Guinea has one of the largest nesting populations of this species.
Binomial: Lepidochelys olivacea
Common: Olive Ridley
Average shell length of 22-30 inches and mass of 80-95 lbs. Carapace is olive green in color and plastron is light greenish-yellow. Has a large head and powerful jaws. Range includes tropical Pacific, Indian, and Atlantic Oceans, prefers to swim on drift lines where there is an abundance of food.
Binomial: Eretmochelys imbricata
Average shell length of 30-35 inches and mass of 95-165 lbs. Dark amber carapace with radiating streaks of brown or black and whitish-yellow plastron. Narrow head with a strongly hooked beak. Carapace has thick overlapping scutes and is serrated along the posterior edge. Range includes coral reefs throughout tropical oceans.
Binomial: Chelonia mydas
Average shell length of 32-48 inches and mass of 144-450 lbs. Carapace is smooth and light or dark brown, sometimes shaded with olive, and brown blotches or streaks. Plastron is yellowish-white. The name originates from the greenish color of their fat which is the result of their herbivorous, sea grass diet. Have small, rounded heads. Range includes tropical and subtropical Atlantic, Pacific, and Indian Oceans.
Marine turtles nest on the 19 km of black sand beaches along the southern shores of Bioko Island’s Gran Caldera Scientific Reserve. The nesting season, which peaks in January, corresponds to the dry season on the Island, beginning in September and extending through April.
The first systematic record of Bioko Island turtle nesting took place from 1996 to 1998. Trained local people from the village of Ureca were responsible for daily counts on the southern beaches. Our attention is now focused on Leatherback and Green Turtles, the most frequently nesting species. Since 2007, Leatherbacks have been tagged with unique identification markers during night patrols. In 2013, the tagging program was extended to the Green Turtles nesting on the Western beaches.