Estimativa populacional e uso do hábitat do boto-cinza (Sotalia guianensis) no litoral sul do Rio Grande do Norte

Four areas are known as of frequent usage by Guiana dolphins (Sotalia guianensis) in the south coast of Rio Grande do Norte state, northeast Brazil: Tabatinga, Pipa, Lagoa de Guaraíras and Baia Formosa. This extension of 40 km of shoreline is under increasing anthropogenic impacts due to continuous development of the coastal areas and vessel traffic. The objective of this study was to investigate aspects of population biology and habitat use of the population of Sotalia guianensis in the south coast of Rio Grande do Norte. It was applied the photo-identification technique and posterior methods of capture-recapture for population estimation (POPAN extension in MARK). The distribution, movement and site fidelity of the dolphins were analyzed trough the geographic information system (GIS) and group characteristics and behavior trough non-parametric statistics. Field work was conducted on board a 10m motor vessel from March 2008 to March 2009. Photo-identification effort was 329h with 113h of direct observation of the dolphins. The population estimatives for each area: Tabatinga: 75 (63-92); Pipa 105 (88-129); Lagoa de Guaraíras: 27 (18-54) e Baia Formosa: 112 (89-129) individuals. Total population estimative was: 223 (192 a 297). High site fidelity was detected for only part of the population (<15%) as low site fidelity and transients individuals were also detected (>20%). It was observed frequent movements between Tabatinga, Lagoa de Guaraíras and Pipa, but not Baía Formosa. This suggests a division in two communities along this shore extension: one in Pipa and other in Baía Formosa. Group size was small, most groups with up to 10 dolphins. The areas were use intensively, only in Lagoa de Guaraíras dolphins were not seen in all field trips. Lagoa de Guaraíras is an area used by small groups exclusively for foraging. In Tabatinga and Pipa dolphins concentrated close to the shore, in the inner sector of the area and the main activity is also foraging. Significant larger groups were seen in socializing behavior but there was no difference in group size between the inner and external sectors of the area. The presence of calves and juveniles were significant greater in the inner areas of Tabatinga and Pipa, confirming the hypothesis that these beaches are also used for parental care. In Baia Formosa dolphins concentrated in the outer sector and foraging was also predominant. Significant larger groups were seen in the outer sector, mainly engaged in mixed behaviors of travel/foraging, possibly in some kind of group foraging. Calves and juveniles were significant more present in the outer sector where group size was also larger. In general there was no difference in area usage and period of the day. Sotalia guianensis has characteristics that make the species vulnerable to human activities such as small population concentrated in patches of suitable habitats restrict to coastal areas. We hope that this study bring new information for the species and help for the adequate management of the area in order to assure the presence of the dolphins as well as its behavior pattern and gene flow betweencommunities.

Fidelidade à área e padrão de associação em Sotalia guianensis, baseado na técnica de foto-identificação

The behavioral patterns follow to environmental changes, including area fidelity and individuals association patterns. Several techniques are used to record these behavioral patterns and the photo-identification has been suggested as a proper tool because of its various advantages. Based on this technique, this research verified, between August of 2005 and January of 2006, area fidelity and association patterns of Sotalia guianensis, at Distrito de Pipa s bays, Rio Grande do Norte State south coast. Besides, we measured the association patterns by using the Jaccard index or Half-Weight Index (HWI). According the observation, 22 individuals were not resighted, 11 were resighted, and 36 new individuals were recorded. Nowadays, 69 individuals are cataloged. The residency rate indicated heterogeneity on studied area permanence and the association patterns between photo-identified seem to be context-specific. In addiction, the comparison of associations between two different age classes showed some individuals more frequently interacting with immature individuals. We also observed fluidity on association patterns among our individuals. We suggest that S. guianensis population from Pipa shows plasticity