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1 April 2008 Social Organization of Marine Tucuxi Dolphins, Sotalia guianensis, in the Cananéia Estuary of Southeastern Brazil
Marcos César de Oliveira Santos, Sergio Rosso
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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-identification 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, whereas groups were composed of up to 60 individuals (mean ± 1 SD = 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 and simple ratio indices were used to investigate associations among S. guianensis as revealed by the entire data set, 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.

Marcos César de Oliveira Santos and Sergio Rosso "Social Organization of Marine Tucuxi Dolphins, Sotalia guianensis, in the Cananéia Estuary of Southeastern Brazil," Journal of Mammalogy 89(2), 347-355, (1 April 2008).
Accepted: 1 September 2007; Published: 1 April 2008

association indices
social organization
Sotalia guianensis
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