Rythme de reproduction interannuel des tortues vertes Chelonia mydas sur les sites de ponte Tromelin et Europa (Océan Indien)

An evaluation of research conducted over the last 15 years on populations of green turtles nesting on Trome/in and Europa Islands (SW Indian Ocean) has been completed (Fig. 1). The first observations (November 1970,pubUshed 1974) ([1], [2]) were followed up by a year-round work in 1973-1974 on Europa [3] and TromeUn. Systematic surveys during the nesting season have been conducted since 1978-1979 on Europa and since 1981-1982 on Tromelin. Each season a 2 to 4 months (November to February) project is set up on both islands in order to assess the number and size of adult females and the production of hatchlings. This longterm research is partially motivated by the development of the turtle ranching on La Réunion. Work by scientist at the nesting beaches includes census of tracks, tagging and intraseason recapture analysis, measurement of females, counting of clutch size and estimating survival rates of hatchUng emerging by day and total survival rates. The number of females tagged (Moneltags) by season and interannual recaptures by site (Table I) provided recapture rates of 2. 1 ta 3.8%, in the same arder of magnitude as those obtained in other intensive tagging studies. The distribution of time-intervals between two recaptures demonstrate a bimodal distribution (4 and 8 years) (Table II). As quoted for Caribbean green turt/es [5] females return for nesting after two, three, four and five or even more (a few femp,le). Regression Unes (predictive) have been computed between curved and straight length of carapace on more than 965 females for each site during the nesting season 1983-1984. Graphie relationship between straight length at times of tagging and recapture, with duration of time-interval in years between the two marking events have been set up (Fig. 2). These figures demonstrate that there is no noticeable length carapace increase between tagging and recapture, as long is the time interval. These locally original results for the area confirm the conc/usions obtained on Tortugero (Costa Rica) green turtle population [6]: increment of carapace length is negligible after the first sexual maturity size.