Marine tucuxi in Sepetiba Bay: Why do they form aggregations?

Between August 2005 and December 2006, 139 boat surveys were conducted in
Sepetiba Bay, Brazil to sample behavioral patterns and environmental parameters during
the occurrence of marine tucuxi groups and aggregations. Aggregations were defined as
several groups gathered in an area totaling more than 100 animals, usually engaged in a
specific behavior. A total of 65 aggregations (x=177) and 192 groups (x=18) were
recorded. Marine tucuxi groups and aggregations differed regarding behavioral activity,
geographical location and age composition. Aggregations were temporal associations of
several marine tucuxi groups performing foraging/feeding activities probably in response
to prey species, abundance, and distribution. Aggregations were primarily located at the
interior of the Bay where local topography may aid dolphins in pursuing and herding
schools of prey. Presence of neonates and calves was highly correlated with aggregations,
reflecting the potential importance aggregations have in the protection, developmental
and learning processes of younger animals.