Dear Marmamers: The following manuscript was recently published. The pdf file is available on request to sotalia@gmail.com Cheers, Marcos C. Santos, M.C. de O. and Rosso, S. 2008. Social organization of marine tucuxi dolphins, Sotalia guianensis, in he Cananéia estuary of southeastern Brazil. Journal of Mammalogy, 89(2):347-355. Abstract: Social organization is an important component of the population biology of a species that influences gene flow, the spatial pattern and scale of movements, and the effects of predation or exploitation by humans. An important element of social structure in mammals is group fidelity, which can be quantified through association indices. To describe the social organization of marine tucuxi dolphins (Sotalia guianensis) found in the Cananéia estuary, southeastern Brazil, association indices were applied to photo-ID data to characterize the temporal stability of relationships among members of this population. Eighty-seven days of fieldwork were conducted from May 2000 to July 2003, resulting in direct observations of 374 distinct groups. A total of 138 dolphins were identified on 1-38 distinct field days. Lone dolphins were rarely seen, while groups were composed of up to 60 individuals (mean + 1SD = 12.4 ± 11.4 individuals per group). A total of 29,327 photographs were analyzed, of which 6,312 (21.5%) were considered useful for identifying individuals. Half-weight (HW) and simple ratio (SR) indices were used to investigate associations among S. guianensis as revealed by the entire dataset, data from the core study site, and data from groups composed of < 10 individuals. Monte Carlo methods indicated that only 3 (9.3%) of 32 association matrices differed significantly from expectations based on random association. Thus, our study suggests that stable associations are not characteristic of S. guianensis in the Cananéia estuary. -- Dr Marcos César de Oliveira Santos Projeto Atlantis, Laboratório de Biologia da Conservação de Cetáceos PROGRAMA JOVEM PESQUISADOR - FAPESP Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista "Júlio de Mesquita Filho" (UNESP), Campus Rio Claro Av 24-A, 1515, Bela Vista, Rio Claro, SP, Brasil, 13506-900. Telefone/Phone: 55-19-3526-4294 Fax: 55-19-3526-4300 E-mail: sotalia@gmail.com Endereço Residencial/Home Address: Avenida 8, Número 1837, Apto 63 Jardim Claret, Rio Claro, SP, Brasil 13503-210