World Status, Exploitation and Trade - WIDECAST

..,INTRODUCTION(feeding) populaLion, Lhia involves long journeyK across open ocean; inothers, for example, the Costa Rica (nesting) Nicaragua (feeding)population, the journey is shorter and primarily coastal. In yet othercases, Hawaii, for example, populations appear to be largely resident withinone geopolitical unit, although reproductive migrations still exist.Blvidence from long term tagging programmes has demonstrated that the speciesshows strong philopatry females tend to return to the same nesting area oneach reproductive migration.As Carr (1975) noted, of the 1300 mature females that had been tagged onAscension at that time none had been found nesting anywhere else.Similarly, of the approximately 30 000 female C . m y das tagged at Tortuguero(Costa Rica), none has been recorded nesting anywhere else (Carr, Carr andMeylan, 1978; Bjorndal, in li tt . , 1987). At the three "turtle islands" inSarawak, of 5,748 nesting records only 3.7% showed a change of island fromthat used on the previous nesting emergence; this is particularly remarkablesince most such changes involved two islands only 500 m apart (Hendr ickson1958). Tn Suriname, no female that had been tagged elsewhere was everfound, and with the exception of "a few" that renested in uhe same season inadjacent French Guiana, no Suriname Green Turtle has been shown to nestelsewhere (Schulz, 1975).However, some cases of imperfect philopatry arc known. There is, forexample, significant shifting between the two main nesting beaches inSuriname (some 70 km apart) both within and between seasons (Schulz, 1975).In Galapagos, some 10% of turtles observed more than once during a seasonemerged on at least two different beaches (though not all emergencesresulted in nesting), while 12% of remigrating turtles moved beaches, halfof these moving islands. Turtles bearing tags either known or assumed to befrom the Sarawak Turtle Islands have reportedly been seen on severaloccasions on the Paloh beaches in north-west Kalimantan, and in the SouthNatuna Islands (Schulz, 1987).One C . mydas observed nesting on Mona Island (Puerto Rica) had previouslybeen tagged on the beach (without nesting) at Aves Island (Venezuela), astraight line distance of some 560 km (Kontos e t al , 1988). Perhaps themost interesting example of imperfect philopatry concerns a female taggedwhile nesting on Tromelin on 30 December 1973 and re-recorded on twosuccessive nights (2-3 December 1982) on a nesting beach on Europa (Le Galland Hughes, 1987). These two islands are well over 2000 km apart by sea.They include, owing to the research programme carried out by French workersover recent years, almost the only regularly monitored C . mydas nest beachesin the entire Indian Ocean. Of the extensive nest beaches on Europa, onlyStation Beach is regularly surveyed. Tn these circumstances, even a singledemonstrated long-distance shift in nest site suggests the possibility thatsuch events may be more frequent, and that local C. mydas populations may beless genetically-closed than is often suspected to be the case.If all nesting females from one population always nested only on one givenbeach, dispersal and colonisation of new or more favourable nesting habitatwould not occur. That dispersal does occur is shown by the fact that bothC. mydas and E. imbricata nest on certain beaches on Krakatau formed sincethe eruption in 1883 (Salm et al . 1982).16