Estudio de la biología de la reproducción de las tortugas marinas del sur de la isla de Bioko (Guinea Ecuatorial)

Abstract

Four sea turtle species nest in 19.4 km of the south coast of Bioko Island (Equatorial Guinea): Chelonia mydas (green turtle), Dermochelys coriacea (leatherbback), Lepidochelys olivacea and Eretmochelys imbricata. The present study summarizes the main aspects of their nesting biology, based on tagging of adult females, nightly surveys and nest census during two nesting seasons. Reproductive success and post-nesting movements are also studied. Main nesting season occurred from October to February, with a peak in December-January. We found some nesting segregation between the two predominant species depending on the characteristics of the beaches. Over 555 (256-<1681) green turtle nesting females were estimated through the mean number of nests (2.99± 1.82) laid by 196 turtles tagged in the 1996-97 season. Nesting leatherbacks ranged from 114 to 230 females. No substantial change in green and leatherback nesting populations were observed in the 1997-98 season. Thus, Bioko Island seems to host one of the most important nesting areas for the green turtle in the atlantic coast of Africa, being also important for leatherbacks. Mean nest size was 107.6? 31.1 eggs (N= 216). Mean incubation period (66.15? 11.15 days in 1996-97, and 61.81 ? 6.85 days in 1997-98) was found to be higher than those recorded in other green turtle populations all over the world. Significant difference in the hatching success between seasons (1996-97: 64.27? 25.35, N= 119; 1997-98: 75.16? 20.67, N= 83) was found, probably due to the different climatic conditions registered. Sporadic storms might have higher impact on the egg development than biotic and abiotic factors affecting the incubation temperature along the incubation period. Although green turtle is a protected species, nests and adult females are exploited in Bioko, even though our evaluation of the number of hatchlings that could reach to sexual maturity showed an overexploitation of this resource. Recaptures of tagged turtles showed a dispersal to several foraging areas, being Corisco Bay (Equatorial Guinea) an important foraging area for Bioko nesting green turtles. Further studies must be carried out at Bioko sea turtle nesting beaches to confirm the conclusions set forth here.