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Marine Turtle Newsletter 39:3-4, © 1986

Nesting Attempts of Chelonia Mydas at Reunion Island (S. W. Indian Ocean)

J. Bertrand¹, B. Bonnet² and G. Lebrun^3
1IFREMER, Délégation de la Réunion, BP 60, 97420 Le Port (Ile de la Réunion), France,
²Laboratoire d'Ecophysiologie, Faculté des Sciences, Université de la Réunion, BP 5, 97490 Sainte-Clotilde (Ile de la Réunion), France, and
³Société Bourbonnaise d'Aquaculture, BP 40, 97436 Saint-Leu (Ile de la Réunion), France

On the morning of 28 June 1986 marine turtle tracks were discovered on a beach of black sand on the southwest coast of Réunion Island (at Etang Salé). These tracks, three in number, were identified as having been made by the same individual green turtle, Chelonia mydas (track width 1.20 m). The three tracks were a few dozen meters apart, with:

• in one of the cases, a very straight line which included an attempt at digging a nest (probably stopped because of a stump);
• a U-shaped route for the second track, also including a deeper digging covering a larger distance (5m);
• a third and longer track (ca. 50m), with 2 digging attempts about 30m apart, less pronounced than the others and situated at the foot of the cliff overlooking the beach.

None of these attempts seems to have resulted in the laying of eggs or even in the digging of a complete nest cavity.

The site is a beach of volcanic origin widely open to the ocean for nearly one km, gently sloping for about 20m and overlooked by a cliff of sedimentary rock 2 or 3m high. It is separated from areas of permanent human activities (villages, roads) by a deep band of trees several hundred meters in width. Owing to these characteristics, this beach represents a unique site for Réunion Island and one which is visited by only a few fishermen.

Refering to the biological context for the species, this turtle came ashore during the winter period (water temperature 24.5°C), which does not correspond to the nesting period characteristic of the green turtle on other sites located at the same latitude (21° 5' S) in the area. Besides, it is curious to note that no later coming ashore resulting in a laying of eggs was noticed during the days which followed the above siting.

Although young and adult green turtles have been sighted regularly in the coastal waters of the island, the discovery of these tracks is an exceptional event in recent times. Since the accounts of travels in the 17th and 18th centuries (in Lougnon 1958), a period during which Réunion Island was still a very important site for marine turtle nesting in the Mascarene Islands, there have been no formal reports of turtles coming ashore. The last reports of such activity, which were never confirmed, date back to the 1950's-1960's. The fact that turtles deserted the beaches of Réunion Island in the 19th century was initially linked to the exploitation of the green turtle throughout the centuries and became more acute as a result of increase in the human population, the urbanization of the coast and the development of tourism on these beaches. A similar situation exists in Mauritius where the last scientific report of nesting dates back to 1977 (Thompson 1981).

The coming ashore of a green turtle on Réunion Island justifies special scientific attention and should be an incentive to take steps to preserve one of the only sites likely to contribute to the return of Chelonia mydas to nest at Réunion Island.

Lougnon, A. 1958. Sous le signe de la tortue. Voyages anciens à lïle Bourbon (1611-1725). Larose ed., Paris, 199 pp.

Thompson, K. 1981. Nesting of the green turtle, Chelonia mydas (Linnaeus) 1758, in Mauritius. Revue Agricole et Sucrière de l'Ille Maurice 60:125-130.