Group size and composition of Guiana dolphins (Sotalia guianensis) (Van Bénèden, 1864) in the Paranaguá Estuarine Complex, Brazil

Abstract

The aim of the present study was to describe the characteristics of Guiana dolphins (S. guianensis) group size and composition in the Paranaguá Estuarine Complex (25° 15' -25° 36' S and 48° 02'-48° 45' W), Paraná State, as well as to verify the existence of relationships between a given environmental variable (water depth, salinity, transparency and temperature) and group size. An area of around 124 km 2 was surveyed by boat from April 2006 to February 2008 in the following subsets of the estuary: Canal do Superagui (~28 km 2 ), Pinheiros bay (~34 km 2 ), part of Laranjeiras bay, which included the Guaraqueçaba sub-estuary (~38 km 2 ), and part of the Mixture Section of the Paranaguá Estuarine Complex (~24 km 2 ). In 45 survey days, a total of 147 hours were spent observing 286 groups of S. guianensis. Groups varied from two individuals to aggregations of up to 90 individuals (mean ± SD: 11.5 ± 14.4 individuals). Solitary individuals were seen only on five occasions (1.7% of all observations). Groups with calves (n = 247) represented 86.4% overall and were more common in all sub-areas when compared to groups without calves. Groups without calves were found in all sub-areas and were usually smaller and composed of up to 12 individuals. A usual group composition of 70% of adults and 30% of calves was observed considering all sub-areas and seasons. No correlations were found between group size and water temperature (Spearman's rank test, r = 0.0059, p = 0.9338), transparency (Spearman's rank test, r = 0.0597, p = 0.9333), depth (Spearman's rank test, r = 0.1421, p = 0.4698), and salinity (Spearman's rank test, r = -0.1938, p = 0.0665). While Guiana dolphin groups were seen in the entire surveyed area, group size varied significantly among the three main surveyed sub-areas (Kruskal Wallis, H 2,196 = 29.85, p = 0.0000). Groups were larger in Laranjeiras bay and smaller in Canal do Superagui. The physical environment, risk of predation, seasonal distribution and abundance of prey are the main possible factors driving larger groups in inner and protected waters.

Population density of Sotalia guianensis (Cetacea: Delphinidae) in the Cananéia region, Southeastern Brazil

“…In the South of Brazil, Filla & Monteiro-Filho (2009) found an average group size of 2.13ind/km² and 2.9ind/km² in the Guaratuba and Paranaguá Bays (state of Paraná), respectively. Also in the Paranaguá Bay, Santos et al (2010) registered group sizes ranging from two to 90 individuals. In the Baía Norte (state of Santa Catarina) the average size found was much larger: 29ind/km² (Daura-Jorge et al 2005).…”

“…Similar results were also found in Paraty Bay (Lodi & Hetzel 1998, Lodi 2003. Santos et al (2010) report that the largest groups of S. guianensis in the protected areas of Paranaguá Estuarine Complex (state of Paraná) occurred due to the local topography, lower predation risk, seasonal distribution and prey abundance. The seasonal variance may be related to changes in the abundance and distribution of the prey, which appears to be strongly influenced by the seasons (Lodi 2003).…”

Using gut contents to assess foraging patterns of juvenile green turtles Chelonia mydas in the Paranaguá Estuary, Brazil

“…Sea turtles are frequently captured in gillnets, especially nets with larger mesh size that have drifted for more than 8 h in the water (Guebert et al 2005). The estuary is considered a nursery ground for fish species (Barletta et al 2008(Barletta et al , 2010 and is an important feeding and resting site for estuarine dolphins and Franciscana (Sotalia guianensis, Pontoporia blainvillei; Santos et al 2010).…”

Parental care behavior in the Guiana dolphin, Sotalia guianensis (Cetacea: Delphinidae), in Ilha Grande Bay, southeastern Brazil

“…Other populations of this species throughout its distribution have been found to include large numbers of groups containing calves. In the Paranaguá estuarine complex (Paraná State), SANTOS et al (2010) reported that 86.4% of all observed groups of Guiana dolphins contained offspring. In Sepetiba Bay, a region adjacent to Ilha Grande Bay where large aggregations of individuals have been observed, NERY et al (2010) reported that 80.3% of all groups observed contained offspring.…”