World Status, Exploitation and Trade - WIDECAST

MEXICONesting season Nesting season at present in MichoacAn extends fromSeptember to December (Alvarado and Figueroa, 1986); it has evidentlyextended into August in the past (see above). However, Brand (cited inParsons, 1962) stated that he had seen turtles (by implication C. mydas )nesting on beaches from February to August. Nesting was recorded in Octoberon the Tres Marias Islands (assuming the species to be C. mydas ) and on theRevilla Gigedo Islands in May (Beebe, cited in Parsons, 1962).Foraging sites There are important feeding grounds in northern Mexico,within the Gulf of California and along the Pacific coast of BajaCalifornia. Cliffton et al (1981) note that historically C. mydas wasabundant along the coasts and in the large bays, saltwater lagoons anddeltas of Baja California, Sinaloa and Sonora, also entering the ColoradoRiver where there are records from 80 km upstream. Carr (1961, cited inParsons, 1962) states, on the basis of examination of stomach contents, thatturtles here feed principally on algae rather than on eel grass and turtlegrass; others (Felger and Moser, 1973; Felger, Moser and Moser, 1980) statethat they feed on eel grass ( Zostera marina ) . ditch grass ( Ruppia maritima ) .marine algae and white mangrove leaves ( Laguncularia racemosa ) . Fishermenin the area note a similar decline in turtle numbers here (a 10-20 folddecrease) since the 1950s to that reported from the nesting grounds inMichoacan. An indication of previous abundance is given by harvest figures:in 1889 the Albatross visited San Bartolome or Bahia Tortugas on the PacificCoast of Baja California at 27°45'N; here 162 Green Turtles "many of largesize" were landed in a single haul of a 600-ft-long seine. Half as manyagain were believed to have escaped before the net was beached. At the turnof the century an estimated 1000 live turtles a month were sent to San Diegofrom Laguna Ojo de Liebre (Scammon's Lagoon).Harvest figures for the area from the 1950s indicate that most turtles werecollected from Baja California from localities including Laguna Ojo deLiebre, Bahia San Bartolome, Bahia de los Angeles, Bahia Magdalena (PuertoAlcatraz) and Bahia San Ignacio (Mercado cited in Parsons, 1962). Most ofthose collected were tajcen north along the peninsula, implying that turtleswere genuinely more abundant in the south than in the north. Some weretaken every month, though most were harvested in June, July and August;Parsons (1962) also stated that Green Turtles were only found in the warmwaters of the Gulf of California during the summer months (but see below).Overwintering sites In the early 1970s large numbers of overwinteringGreen Turtles were discovered off the south shore of Tiburon Island in theGulf of California off the Sonoran coast; the turtles were lying motionlessat depths of 10-30 m. Exploitation of these turtles began in 1975 and by1980 they had reportedly been drastically depleted (see below).Migration Tagging returns from turtles marked at the Michoac4n breedingsites indicate that there may be two subpopulations nesting here, onefeeding in the Gulf of California and adjacent waters (see above) and theother foraging south off Central America: as of March 1986, of the 28 femaleChelonia tagged at Michoacan which had been recovered and reported away fromthe nesting grounds, 22 were recovered from Central America (16 from ElSalvador, four from Guatemala, one from Nicaragua, one from Costa Rica), onefrom Colombia and five from waters off Mexico north of Michoacan (two fromthe Gulf of California, two from Sinaloa, one from the Islas Tres Marias)(Alvarado and Figueroa, 1986 and 1987).357