JOANA F. AUGUSTO
Graduate Student

E-mail: jaugusto@ispa.pt
Phone: + 351 91 433 37 15

Masters Thesis in Marine Ecology
Analysis of social structure, group composition and associations in the resident Bottlenose Dolphins (Tursiops truncatus) population in the Sado estuary
The bottlenose dolphin (Tursiops truncatus) population that inhabits the Sado estuary is the only resident population in mainland Portugal, and one of the few in Europe. Its numbers have been declining, with 26 individuals photo-identified
during the course of this work.
This population is aged, since it’s comprised in more than three quarters by adults. The sex ratio is uncertain because the sex of more than a half of the individuals is unknown.
The group structure was analysed by size and age class. The average group size is 10.06, a common value in this species, but high relative to the population size. This may be related to the decrease of competition resulting from the decline of population size, together with a habitat of stable resources. The most frequent group type presents all age classes.
The association analysis was conducted with the SOCPROG application. The associations, using the group (individuals in the same area) as sampling unit are “preferred” (this is, different from random) and “long term” (stable on a long term). An average coefficient of association for the population of 0.61 was obtained. The coefficients of association are similar between classes and sexes, and without a clear subunit partition of the population. This uncommon structure might be related to the population’s phylopatry, together with its reduced size. The fission-fusion nature of the groups in this population is enhanced in temporal analysis (on a short term), where rapid dissociations and casual companions are predominant.
The relation between estuary area and behaviour class was also studied, even though the data obtained were not enough for a systematic analysis. Nevertheless a selective use of the estuary during the sampling period was detected, with avoidance of the downstream part of the north channel.

:: Conference Presentations

AUGUSTO, J., LOPES, P., DOS SANTOS, M. E. “Análise da composição dos grupos e das actividades dos golfinhos-roazes na região do estuário do Sado”. Oral presentation at the 8º Congresso Nacional de Etologia, Lisbon, Portugal, January 2008.

AUGUSTO, J., LOPES, P. R., DOS SANTOS, M. E. “Composition and Group Structure of a Small Endangered Resident Population of Bottlenose Dolphins (Tursiops truncatus)”. Poster presentation at the 22nd European Cetacean Conference, Egmond aan Zee, Netherlands, March 2008.