Group structure of Guiana dolphins, Sotalia guianensis (Cetacea, Delphinidae) in Ilha Grande Bay, Rio de Janeiro, southeastern Brazil

A groundbreaking study reveals that Guiana dolphins (Sotalia guianensis) in Ilha Grande Bay, Brazil, exhibit highly variable group structures influenced by behavior and season. Researchers observed 1,314 groups, with a staggering 94.4% containing calves—a record high for the species—suggesting a protective strategy for underdeveloped individuals. Group sizes averaged 17.6 members, while cohesion levels varied significantly with behavioral states and seasonal changes. This work sheds light on the complex social dynamics of this 'data deficient' IUCN-listed species, offering critical insights for conservation efforts in an area increasingly threatened by human activities.

Tardin, R., Galvão, C., Espécie, M., & Simão, S. (2017). Group structure of Guiana dolphins, Sotalia guianensis (Cetacea, Delphinidae) in Ilha Grande Bay, Rio de Janeiro, southeastern Brazil. Latin American Journal of Aquatic Research, 41(2), 313–322. https://doi.org/10.3856/vol41-issue2-fulltext-10