Genetica 121: 195–206, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 195 Conservation genetics of the east Pacific green turtle (Chelonia mydas) in Michoacan, Mexico Omar Chassin-Noria 1 , Alberto Abreu-Grobois 2 , Peter H. Dutton 3 & Ken Oyama 1 1 Centro de Investigaciones en Ecosistemas, UNAM, Antigua carretera a Patzuaro 8071, Colonia Ex Hacienda de San Jose de la Huerta, C.P. 58190, Morelia, Michoacan, Mexico (Phone: +52-443-322-2704; Fax: +52-443-322- 2719; E-mail: chassin@oikos.unam.mx); 2 Instituto de Ciencias del Mar y Limnologia UNAM, Unidad Academica Mazatlan, A.P. 811 C.P. 82000, Mazatlan, Sinaloa, Mexico; 3 NOAA-NMFS Southwest Fisheries Science Center 8604 La Jolla Shores Drive, La Jolla, CA 92038, USA Received 8 July 2003 Accepted 9 November 2003 Key words: black turtle, Chelonia mydas, east Pacific green turtle, effective population size, genetic diversity, genetic structure, microsatellites, mitochondrial DNA Abstract The main continental nesting rookeries of the east Pacific green turtle (EPGT), Chelonia mydas, on the Michoacan (Mexico) coast suffered drastic population declines following intense exploitation in the 1960s–1970s with annual abundance of nesting females plummeting from about 25,000 to an average of about 1400 between 1982 and 2001. Analyses of data from three nDNA microsatellite loci and 400 bp mtDNA control region sequences from a total of 123 nesting females sampled from four Michoacan rookeries found no evidence of population sub-structuring. The recent order of magnitude reduction in the population size shows no apparent impact on genetic diversity in either control region sequences (overall h = 0.48; π = 0.0036) or microsatellite loci (overall N a = 20.8; H exp = 0.895). Our estimates of annual effective female population size (N ef ; from θ = 2N e μ) of 1.9–2.3 × 10 3 , in spite of being an order of magnitude below historical records, appear to be sufficient to allow recovery of this population without significant loss of genetic diversity. These findings highlight the importance of continued conservation to reverse the decline of this population before it becomes vulnerable to genetic erosion. Abbreviations: AB – Arenas Blancas; COL – Colola; EPGT – east Pacific green turtle; MAR – Maruata; mtDNA – mitochondrial DNA; nDNA – nuclear DNA; PN – Paso de Noria. Introduction The green turtle, Chelonia mydas, is distributed in tropical and sub-tropical waters and nests on beaches of five continents between latitudes 30 ◦ N and 30 ◦ S (Marquez, 1990; Hirth, 1997). Females of the species exhibit a strong tendency for natal homing and nest site fidelity (Meylan, Bowen and Avise, 1990; Bowen et al., 1995) that results in significant genetic differ- entiation among rookeries (Encalada et al., 1996). In the east Pacific the species has nesting sites from the Galapagos Islands (Ecuador) northward to Michoacan and the Revillagigedos Islands (Mexico), where it is known as the east Pacific green turtle (EPGT) or ‘black turtle’ (Pritchard and Mortimer, 1999). These individuals exhibit morphological characteristics that distinguish them from other C. mydas (e.g., adult car- apace is much darker, domed, and with indented edges above the hind limbs; mature individuals are smaller and the breeding females lay fewer eggs; Hirth, 1997). These meristic features and multivariate morpholog- ical analyses have led some authors to consider the EPGT either as a full, separate species, C. agassizii (Bocourt, 1868; Pritchard, 1999), or a sub-species, C. m. agassizii (Marquez, 1990; Kamezaki and Matsui, 1995). However molecular genetic studies, which have demonstrated their utility in resolving major taxo- nomic and evolutionary controversies in marine turtles