World Status, Exploitation and Trade - WIDECAST

REUNION AND ILBS EPARSBScatch. This level of harvest may well be a threat. Hughes (1971b) assertedthat a great number of nests on Europa are destroyed by later nesters, andinferred from this density-dependent mortality that the population couldwithstand increased hunting pressure. In fact, the extent of mutual nestdestruction has been little investigated: Hughes (1970) stated that thenumber so destroyed was "not inconsiderable", but was not able todemonstrate the proportion of nests involved; Servan (1976) actuallyrecorded only three such instances, and noted that some other nests weredestroyed by sea water.TROMELINPOPULATION:Chelonia mydasNesting sites Beaches used by nesting turtles extend for some 1.6 kmaround the north-western half of the island; most nesting takes place on thenorth-east and south-west beaches, and very little at the north-western tipof the island (Vergonzanne et al . 1976). The nesting area is small enoughto allow comprehensive monitoring of nesting activity.Nesting numbers Hughes (1974, Table 15) estimated an annual nestingpopulation at Tromelin of 200-400 females over the 1970-1971 season (basedon field work between 15 October and 6 November). Batori (1974,unpublished; also cited by Vergonzanne et al . 1976) recorded about11 females nightly during the winter months (July-September) of 1973 andthree nightly in June-July 1974; in summer 1973-1974 (November-January)Batori recorded around 54-148 females nightly. Hughes later (1976)estimated the annual total at around 2000. Hughes (1982b) cited otherestimates from Lebeau et al (not seen) of 1000 females in 1977, and around4400 in 1978. Between 86 and 116 females nightly were recorded by Bonnet(unpublished) in November-December 1980. More recently, Le Gall et al.(1985 and 1986), have provided nesting and hatchling estimates for the years1981-1984, based on consistent field and analytical methods. Salientfigures from this work are given in Table 172.Le Gall et al (1986) report a close correspondence between nestingestimates obtained by the more traditional methods, cited above, and amultiple capture-recapture method. The results were particularly close inthe case of Tromelin, and a little less so in the case of Europa (where onlyone beach can be monitored thoroughly). These authors give an overall peakquarter estimate for Tromelin of 730-1350 females (95X confidence limits).Trends in nesting numbers The available data show no clear trend innumbers. The number of tracks recorded appeared to be declining until1985-86, but the following season, 1986-87, was the highest recorded.Nesting season Some nesting occurs through much of the year, but mostlybetween November and May, with 50-70% of all activity taking place duringNovember-January (Bonnet et al. . 1985; Le Gall et al. . 1985).Foraging sites A substantial proportion of the population nesting atTromelin appears to be migratory, using foraging grounds around Madagascarand the Mascarenes. Although adult turtles have been observed feeding onalgae around Tromelin, food resources appear inadequate to support largenumbers throughout the year (Bonnet, 1985 and in litt. . 22 April 1987).443