Spatial distribution and activities of the estuarine dolphin Sotalia guianensis (van Bénédén, 1864) (Cetacea, Delphinidae) in Pontal Bay, Ilhéus, Bahia, Brazil

Abstract

We analyzed the influence of time, tide and water depth on the activity and spatial distribution of estuarine dolphins Sotalia guianensis in Pontal Bay, Ilhéus, Brazil. Direct observations were carried out at four fixed points from January to December of 2006. Estuarine dolphins were sighted in 11 out of 12 months and in 30% of 181 sampling periods. The average group size, which was 3.75 ± 1.59 (n = 64), did not vary significantly by month (Kruskal-Wallis, H = 10.6729; p = 0.3836). Infants and adults represented 18 and 82% of the individuals whose age we were able to determine, respectively. Estuarine dolphins were more frequently present than expected in areas deeper than 3 m (regression GLM, z = 3.773; p = 0.0002). The animals were more frequently observed between 7:00 and 8:00 AM and between 3:00 and 5:00 PM (X² = 83.815; p < 0.0001). Their presence in the bay tripled between the fourth hour of the flood and high tide, remaining elevated during the ebb tide (X² = 22.152; p = 0.02). The tide also influenced the animals' feeding and travelling direction, mainly toward the open see during the flood and to the back of the bay during others stages. Further studies are necessary to analyze the influence of the hydrographic characteristics of Pontal Bay on the spatio-temporal distribution of estuarine dolphins and their prey.

Tidal and seasonal influences in dolphin habitat use in a southern Brazilian estuary

“…On the other hand, the Guiana dolphins did not show a well-defined pattern in relation to the tidal currents, using inner areas in the early ebb stage and remaining near the mouth of the bay in the late flood stage. A similar pattern was observed for Guiana dolphins in Pontal Bay in Bahia, Brazil, where they moved towards the bay mouth during flood tide (Santos et al 2010). Although the counter-current foraging strategy has already been described for T. truncatus (Shane 1990), apparently movement following the direction of the current is most common (e.g.…”

Cetaceans registered on the coast of Ilhéus (Bahia), northeastern Brazil

“…12,no. 1 and 39° 02' W) with 40 km 2 , formed by the junction of the Cachoeira, Fundão and Santana Rivers (Santos et al 2010), which divide the city into two parts: the southern and northern area. The areas closer to the mouth of the estuary have no vegetation and make up the urban area.…”

Habitat use and conservation of an Endangered dolphin

“…Mendes et al 2002, Johnston et al 2005a, or predominantly oriented into the tidal stream (dos Santos et al 2010). Our model results suggest a significant effect of tide, but that this is much less important than location, season, or time.…”

“…Hours after high tide Acoustic detection per day While several studies have examined how season, time and tide influence dolphin habitat use (e.g. Marcoux et al 2009, dos Santos et al 2010, few have had sufficient data to assess quantitatively the interactions among these factors and their relative importance. As indicated above, evidence of seasonal variation in habitat use is unsurprising, particularly at the small scale of this study, and has been noted in several other studies of Hector's dolphin (e.g.…”