Latin American Journal of Aquatic Mammals (LAJAM)
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Note on the group size and behavior of Guiana dolphins (Sotalia guianensis) (Cetacea: Delphinidae) in Marapanim Bay, Pará, Brazil
No full textNatural history of dolphins of the genus Sotalia
No full textGeneral biology, including food habits, reproduction, age and health of the dolphins of the genus Sotalia, are reviewed according to current scientific knowledge. At least 25 teleost fish families, 5 cephalopod families and 1 crustacean family are included in the diet of the Guiana dolphin (S. guianensis), while up to 13 fish families were identified in the stomachs of the tucuxi (S. fluviatilis). Among the fish consumed by Sotalia spp., the schooling fish are the most common ones and both dolphin species use similar foraging strategies. However, due to the completely different ecosystems used by them, prey species consumed by these dolphins are also different. The maximum age of incidentally caught Guiana dolphin was 30yr and the maximum age estimated in the tucuxi was 43yr. The maximum total body length and weight reached by S. guianensis was 222cm and 121kg, respectively, and for S. fluviatilis 152cm and 53kg, respectively. Sexual maturity in the Guiana dolphin was estimated to occur at 170-180 cm in males, and 160-169 cm in females, while onset maturity in the tucuxi occurs at around 140cm in males and 132-137 cm in females. Ovulation apparently occurs only in the left ovary of the tucuxi, while both ovaries of the Guiana dolphins are functional. The proportion of testes mass in relation to total body mass in adult males can reach up to 5% in the tucuxi, and 3.3% in the Guiana dolphin, suggesting a promiscuous mating system with sperm competition in both species. Although seasonal birth peaks can occur in Guiana dolphins, they seem to reproduce throughout the year. However, the tucuxi presents defined birth seasonality, with most females giving birth during the low-water season in the Amazon. We suggest maintaining S. fluviatilis in the ‘Data Deficient’ category of the IUCN Red Data Book. Nevertheless, due to the recent recognition of S. guianensis as a species, its conservation status has not been assessed yet. This species, however, deserves special attention as it is strongly subjected to anthropogenic pressures throughout its distribution
Mitochondrial DNA diversity, differentiation and phylogeography of the South American riverine and coastal dolphins Sotalia fluviatilis and Sotalia guianensis.
No full textHere we consider the phylogeography and population structure of the South American coastal and riverine dolphins, Sotalia guianensis and Sotalia fluviatilis, based on samples (n = 76) collected across more than 9000km of the species distribution. Phylogenetic reconstruction of 31 distinct haplotypes based on a combined analysis of two mitochondrial gene fragments (1052bp) revealed clear genetic differences between riverine and coastal individuals consistent with species-level ranking. Within the coastal species, a spatial analysis of molecular variance of the control region sequences showed significant regional population differentiation (FST = 0.4; FST = 0.6; P<0.001). The highest mitochondrial diversity among costal population units was found along the Caribbean Coast of Colombia and Venezuela. The genetic distinctiveness of the Maracaibo Lake (Venezuela) population has conservation implications regarding the threats faced by the animals in this region, including oil exploitation. Brazilian populations of Sotalia showed the lowest mitochondrial diversity and differentiation among the coastal species warranting further investigation. The Amazonian populations showed the highest mitochondrial diversity overall, suggesting a surprisingly large effective population size (Nef) and relatively high female gene flow throughout the sampled regions of the main river and its tributaries. From our results, at least two different conservation strategies need to be developed for each of the proposed sister-species. For the coastal groups, characterized by restricted gene flow and very localized populations along the Caribbean and Atlantic Coast of South America, it is advisable to work at a local level in order to improve the fishing practices and prevent frequent dolphin entanglement in nets. For the Amazonian groups, priority must be given to maintain the connectivity detected between regions. Obstacles to connectivity, including hydroelectric and dam construction, as well as excessive boat traffic, could affect the future of these populations
Residence patterns of the Guiana dolphin Sotalia guianensis in Babitonga bay, south coast of Brazil
No full textPhoto-identification and video-identification techniques were applied to study the residence of Sotalia guianensis in the Babitonga Bay, north coast of Santa Catarina State. From November 2000 to February 2003 a photo-identification effort was conducted trough 21 months, with additional video-identification conducted from August 2003 to August 2004, totalling 34 months of identification effort. Fifty-one different animals were identified with residence rates varying from 2.9% (n = 1 sighting) to 67.6% (n = 23 sightings). During the four years it was found that more than 30% (n = 16) of identified individuals were observed during three years, and 25% (n = 13) only were seen within one year. Considering previous studies, the longest period of residence reached eight years for one individual. Due to the high rates of resightings observed for most of the animals and the small percentage of animals only seen once, it is clear that S. guianensis is resident year-round in the studied area
Update on the freshwater distribution of Sotalia in Colombia, Ecuador, Peru, Venezuela and Suriname
No full textReport of the Working Group on Distribution, Habitat Characteristics and Preferences, and Group Size
No full textSounds produced by the tucuxi (Sotalia fluviatilis) from the Napo and Aguarico rivers of Ecuador
No full textThe acoustic structure and repertoire of the tucuxi (Sotalia fluviatilis) remain poorly studied. This lack of information limits our understanding of how acoustic signals evolved and the factors that promote variation across and within populations. Using a broadband recording system, we recorded 30 whistles from tucuxis in the Napo and Aguarico Rivers, Ecuador. Our results show that Ecuadorian tucuxis emit a variety of sounds including whistles, echolocation clicks, and pulse sounds. Whistles structure varied with respect to other populations described in previous studies, providing preliminary evidence of geographic variation. In addition, this study provides evidence of high order harmonics in whistles (up to 80kHz) highlighting the importance of broadband recording systems
Report of the Working Group on Major Threats and Conservation
No full textReport of the Working Group on Major Threats and Conservatio
Habitat use of the Guiana dolphin, Sotalia guianensis (Cetacea, Delphinidae), in the Caravelas River Estuary, eastern Brazil
No full textHabitat use patterns of the Guiana dolphin (Sotalia guianensis) were assessed in the Caravelas River Estuary, eastern Brazilian coast (17°54’S, 39°21’W). During 191 surveys (2002-2004), 187 groups were sighted. The Arcview 3.1 software was used to create a GIS environment that included the distribution of dolphin sightings, a 5x5km quadrats grid, and the bathymetry of the study area. Each quadrat was characterized according to environmental variables such as depth, contour index, distance from sand banks and distance from the coastline. The Caravelas River mouth was found as the core area of the dolphins. Guiana dolphins did not use the several classes of environmental variables homogeneously, occurring more frequently in shallow waters, closer to sand banks and closer to the coastline. Also more dolphins occurred in areas with flatter bottoms and in waters with salinity ranging from 35 to 38ppm, despite dolphins being sighted in waters 14km inside the river. Dolphins used a wide range of habitat types but the Caravelas River mouth seems to propitiate the most adequate conditions for foraging strategies or concentration of prey
