World Status, Exploitation and Trade - WIDECAST

INTRODUCTIONMigration and philopatry: malesOverall, whilst there is very little direct information on long distancereproductive movements of adult male sea turtles, the few data that areavailable are consistent with the pattern demonstrated for adult females.Virtually all tagging programmes have exclusively involved tagging femaleson the nesting beach; very few males have ever been tagged and, in thegeneral absence of suitable tag-return data, there is very little evidencefor philopatry in males. Males, of course, contribute half of the totalgenetic constitution of the population. It may well be the case that malesfeed and migrate with the females from each population, but perhaps someproportion of them disperse widely and subsequently join any convenientfemale aggregation.The best evidence available on male movements in Chelonia mydas relates tothe apparently isolated C. mydas population in Hawaii (Dizon and Balazs,1982). Two males, tagged in 1975 and 1970, were recorded to remigrate tothe same nest area in later years, in 1976 and 1977, and in 1979,respectively (radio telemetry indicated that both males and females remainclosely associated with the nesting beach area during the nesting season).Overall, during the ten-year period up to 1982, 294 turtles tagged at theHawaii nesting ground have been re-sighted, and this includes 87 males(Balazs, 1983). Seven of these males have been shown to make long distancemigrations between feeding grounds and the nesting area (or vice versa), andone of the seven has been recorded to make the return journey from feedinggrounds to the nesting area and back (Balazs, 1983). Three of 575 malestagged in the Galapagos, presumably while breeding, were subsequentlyrecaptured; one in Costa Rica and two in Peru (Green, 1984a). Similarly,two males tagged on Scilly in French Polynesia were subsequently recapturedin Fiji; females from this population have also been recaptured at othersites in western Oceania (Anon, 1979).Hawksbill migrationAlthough little concerted tagging of Hawksbills has been undertaken, and isdifficult in the absence of dense nesting aggregations, there is littleevidence as yet to counter the prevailing notion that the species tends tobe a mainly sedentary coral reef dweller; equally, there is little evidencesubstantiating the idea. A few examples of apparently purposefullong-distance migration are known (Parmenter, 1983). These include:movement between the Solomon Islands and Papua New Guinea, the TorresStraits and the Solomons, Sabah and the central Philippines, Tortuguero(Costa Rica) and Nicaragua. It may well be that the small number ofreported long distance movements is a simple function of the small number ofHawksbills that have been tagged and recaptured, and it is possible thatindividuals move long distances between feeding and nesting areas, and amongdifferent feeding areas, more commonly than observations indicate.Maturation periodCaptive-reared Green Turtle females (at Cayman Turtle Farm) become sexuallymature at a minimum of 8 or 9 years; the mean age of maturation at CTF isprobably greater than this (Wood and Wood, 1980), perhaps 10 or 11 years ormore. Until quite recently it had widely been assumed that maturation inthe wild occurred after a similar period (sources cited by Hirth, 1971).17