Observations on sea turtles at Aldabra Atoll

Abstract

This paper is a preliminary report based on observations made from January to July 1968 and on expedition notes from August 1967 to November 1968. The majority of the work was carried out on adult green turtles which had been harpooned and captured by the Seychellois turtlemen at Aldabra. A small number of observations were made on nesting females and hatchlings of the same species. Males are, on average, smaller than females; this is the reverse of the expected situation and may be due to the fact that more males than females are captured. The relevance of various body proportions is discussed, as are the results of regression analysis of the measurements. Coloration of the adult carapace is extremely variable, but certain colour characteristics are strongly correlated with sex; a predictive index for sex determination is presented. Green turtles at Aldabra have similar breeding biology to other populations. Hatchling and egg measurements reflect the same trends shown by the adult females. A number of different organisms were found on adult green turtles: barnacles, leeches, isopods, green algae, and red algae. In addition, tabanids and mosquitoes were found on turtles above water. Sharks and ghost crabs are probably important predators of adults and young respectively. Only one internal parasite was found. Incidental observations were made on hawksbills. The first recorded specimen of a loggerhead from Aldabra was obtained. Information from Seychellois turtlemen relating to sea turtles at Aldabra is presented; economic importance and problems of conservation are raised.