Acta Zoologica (Stockholm) 85: 223– 232 (October 2004) © 2005 The Royal Swedish Academy of Sciences  Abstract Sanvicente-Añorve, L., López-Sánchez, J.L., Aguayo-Lobo, A. and Medrano- González, L. 2004. Morphometry and sexual dimorphism of the coastal spotted dolphin, Stenella attenuata graffmani, from Bahía de Banderas, Mexico. — Acta Zoologica (Stockholm) 85: 223–232 External measurements and size differences between the sexes were examined in the coastal spotted dolphin, Stenella attenuata graffmani, in Bahía de Banderas, on the Mexican Pacific coast. The dolphins were collected by local fishermen and 29 external characteristics were measured by members of the Marine Mammals Laboratory, University of Mexico. The length of each characteristic with respect to total length was analysed through adjustment of the data to a power equation. A stepwise discriminant analysis was applied to the absolute values and to those expressed as proportions to analyse the differences between the sexes. Results indicate that growth in these dolphins is generally negatively allometric, and most of the characteristics measured were, in both absolute and proportional terms, greater in male dolphins than in female dolphins. As found in many species of odontocetes, the discriminant analysis showed that the main differences between the sexes for this coastal subspecies include the relative positions of the umbilicus, the genital aperture and the anus.The morphometric data provided by this study, corresponding to 29 specimens of S. a. graffmani collected in a restricted locality of the Mexican Pacific coast, are particularly interesting to studies documenting latitudinal morphological differences in the coastal spotted dolphin. Laura Sanvicente-Añorve, Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Apdo. Postal 70-305, 04510 México, D.F. Mexico. E-mail: sanvi@mar.icmyl.unam.mx Blackwell Publishing, Ltd. Morphometry and sexual dimorphism of the coastal spotted dolphin, Stenella attenuata graffmani, from Bahía de Banderas, Mexico Laura Sanvicente-Añorve, 1 José Luis López-Sánchez, 1 Anelio Aguayo-Lobo 2 and Luis Medrano-González 3 1 Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Apdo. Postal 70–305, 04510 México, D.F. Mexico; 2 Instituto Antártico Chileno, Plaza Muñoz Gamero 1055, Punta Arenas, Magallanes, Chile; 3 Universidad Nacional Autónoma de México, Facultad de Ciencias, Apdo. Postal 70–572, 04510 México, D.F. Mexico Keywords: body characteristics, dolphins, eastern Pacific Ocean, sexual differences, Stenella attenuata Accepted for publication: 9 August 2004 Introduction The pantropical spotted dolphin, Stenella attenuata (Gray, 1846), inhabits the tropical oceans. These dolphins form schools of hundreds or thousands of individuals in the oce- anic region of the Pacific Ocean (Scott and Cattanach 1998), but are also found in coastal areas, both along continental coasts and around oceanic islands, forming schools of less than 100 individuals (Perrin 1975; Acevedo and Burkhart 1998; Baird et al. 2001). Most of the studies on this species have been carried out on the offshore form because the association of these dolphins with the yellowfin tuna Thunnus albacares ( Bonnaterre, 1788) has led to a high rate of incidental capture of these animals.Thus, its coloration pattern ( Perrin 1975), distribution and morphological characteristics ( Perrin et al. 1985, 1994), growth, reproduction and mortality (Perrin et al. 1976; Wade 1995; Archer et al. 2001), feeding habits (Robertson and Chivers 1997), migratory movements (Perrin et al. 1979) and evasive behaviour (Heckel et al. 2000) have been