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Sotalia fluviatilis (Gerais and Deville, 1853)
English = Tucuxi Spanish = Tucuxi, bufeo negro
Conservation status of Tucuxis:
- Tucuxis are listed in Annex 1 (Endangered) of the Convention on International Trade in Endangered Species;
- Tucuxis are listed in Annex C1 (strongest category of protection) of Regulation 3626/82 of the European Union;
- Tucuxis are protected by the Marine Mammal Protection Act of the United States of America;
- Tucuxis are listed as “insufficiently known” by the International Union for Conservation of Nature and Natural Resources,
- Tucuxis are protected in Peru protected since 1996 by national law
Distribution in of Tucuxis in Peru:
Northern Peruvian Amazon rainforest
Present threats for the Tucuxis:
- incidental catches in gillnets
- contamination by sewage and gold mining
- overfishing of rivers
Natural history of the Tucuxi
The word “tucuxi,” comes from “tucuchi-una” from the Tupi language of the Mayana indigenous group in the Amazon Region.
The appearance of the tucuxi resembles that of a smaller bottlenose dolphin. The tucuxi is light grey to bluish-grey, on the back and pinkish to light grey on the belly, with a distinct boundary between the mouth gape and the flipper’s leading edge. On the sides, there is a lighter area between the flippers and the dorsal fin. The dorsal fin is triangular and may be slightly hooked at the tip. The beak is moderately slender and long. Body size reaches 210 – 220 cm in marine and 152 cm in riverine species.
Alexander von Humboldt was probably the first naturalist to document the presence of coastal dolphins that ascended the mouths of rivers in Venezuela. During his travels in northern South America, between 1799 and 1804, he noted the presence of relatively small dolphins with prominent dorsal fins about 130 km up from the mouth of the Orinoco River, in San Fernando de Apure, Venezuela.
At present, the taxonomy of these dolphins remains unresolved. Although five species were described in the late 1800s, only one species is recognized currently (Sotalia fluviatilis) with two ecotypes or subspecies, the coastal subspecies (Sotalia fluviatilis guianensis) and the riverine subspecies (Sotalia fluviatilis fluviatilis). Recent morphometric analyses however, as well as mitochondrial DNA analysis, suggested recognition of each subspecies as separate species, the marine Sotalia guianensis and the riverine Sotalia fluviatilis.
The pronounced differences in salinity between the riverine and coastal-estuarine waters, as well as the changes in the water level at different times of the year, represent different selective pressures. Salinity ranges from less than 0.05 ppm (parts per million) in the Amazon River to over 35 ppm on the Atlantic coast of Brazil with a steep cline in the last 200 km of the mouth of the river. For example, although both coastal and riverine Sotalia prey mostly on fish from the same families (i.e., Sciaenidae and Clupeidae), they prefer different species found exclusively either in freshwater or saltwater, and no overlap in prey species has been observed in diet studies.
The dominant echolocation frequency of coastal Sotalia (55–65 kHz) is higher than that of riverine Sotalia (40–45 kHz), and the signal of thelatter is more similar to that of the sympatric Amazon River dolphin (Inia geoffrensis) = (36–46 kHz).
Finally, adaptation to seasonal fluctuation in the water levels of the Amazon River and its tributaries has influenced the seasonality of reproduction in riverine Sotalia, perhaps contributing to an incipient prezygotic isolating mechanism. A high proportion of births in riverine Sotalia occur during the dry season (October–November) when water levels are low. Births in coastal Sotalia occur year round with a peak in the rainy season (May–November) in some localities. Duration of gestation is also longer in coastal individuals, 11.6–11.7 months, compared to 10.0–10.3 months in riverine Sotalia.
Other differences in reproductive parameters include ovarian activity restricted to the left ovary in riverine Sotalia and activity in both ovaries in coastal Sotalia. Furthermore, seasonal testicular activity has been suggested in riverine Sotalia, whereas it has not been detected in coastal Sotalia.
Based on geological evidence, it has been estimated that about 2.5 mya, the ocean level was 180 m above the present and since then a general trend of descending sea level has occurred. From 2.5 mya to the present, it is thought that the entire Amazon basin underwent alternating periods of ponding with sedimentation as well as regional erosion. This series of ponding events, accompanied by tectonic activity in the western Amazon, has been proposed as the “Amazon Lagoon” (Lago Amazonas) hypothesis.
According to this hypothesis, the Amazonian lowland could have been covered by water until approximately 750,000 B.P.. Tectonic events, climatic change (cooling) and environmental change have been proposed as the cause for the transition of the Amazon Basin from a large lake to a braided fluvial system in the early Pleistocene. It was suggested that these transitional events isolated the riverine Sotalia from the coastal populations, maintaining a possible connection only in the mouth of the Amazon River, and promoting the divergence of these two species closer to the date of 750,000 B.P.
The relatively recent divergence of Sotalia is also suggested by comparison with the wider distribution of Inia. Although the family Iniidae is ancient, having occupied the Amazon drainage for around 15 million years, divergence of the Bolivian Amazon subspecies (Inia geoffrensis boliviensis) is more recent, having occurred between 5 and 6 mya by the formation of the Madeira-Mamoré rapids. As Sotalia is not found in the Bolivian Amazon above the rapids, this seems to suggest an upper time limit of 5 mya for its occurrence in the Amazon.
A similar upper bound is suggested by the divergence of the Amazon and Orinoco subspecies (Inia geoffrensis geoffrensis and Inia geoffrensis humboldtiana). Connectivity between the Amazon and Orinoco Inia subspecies is suspected through the Casiquiari Channel, which connects the Upper Orinoco and the upper Rio Negro, one of the main tributaries of the Amazon River. This is, at present, the only possible point of contact between the Amazon and Orinoco river basins after isolation of the Orinoco drainage from the main Amazon drainage initiated with the uplift of the Eastern Andean Cordillera in the Late Middle Miocene (ca. 12 mya) and continued with the uplift of the Merida Cordillera in the Late Pliocene (5–3.4 mya).
If Sotalia entered the Amazon and expanded toward other tributaries, and the divergence of the coastal and riverine proposed sister species occurred between 5.0 and 2.5 mya, we would expect Sotalia to be found in the upper Orinoco, with a distribution similar to that of I. g. humboldtiana and similar connectivity between Orinocoan and Amazonian Sotalia populations. To date, presence of Sotalia in this region has not been confirmed and sightings of Sotalia (presumably coastal transients) are restricted to the lower Orinoco and its mouth.
Riverine Sotalia inhabit all types of water (“whitewater”, “clearwater”, and “blackwater” rivers) of the Amazon region, so physical factors such as visibility and pH appear not to affect their distribution directly. Riverine Sotalia are found in the main channels of rivers as well as in larger lakes where access is not limited by a narrow or shallow channel. They generally do not enter the flooded forest. Rapids and fast-moving turbulent water are also avoided. Sotalia show a distinct preference for junctions of rivers and channels.
The two species of Sotalia seem to have a similar social structure. The marine species is reported to occur in groups of as many as 30 individuals. Calves are usually observed in small groups of three (one calf and two adults) or four (two calves and two adults).
In one study the riverine form occured in groups of one to six individuals in 55% of the observations. Groups of more than nine animals are seen on rare occasions. In preliminary observations of Mundo Azul in the Amazon river groups sizes ranged between 3 and 12 animals. Other researchers reported an overall mean group size of 3.9 individuals in the upper Amazon river.
In Brazil, calving in the riverine form apparently occurs primarily during the low water period, October to November. Little else is known of the species’ reproduction.
Marine Sotalia from south-east Brazil feed on a diet of pelagic clupeids (Trichurus lepturus and Pellona barroweri), demersal sciaenids (Cynoscio spp., Porichthys porosissimus, Micropogonias furnieri) and neritic cephalopods (Loligo spp. and Lolliguncula brevis). In Santa Catarina dolphins are known to feed on anchovies.
In the Amazon region, Sotalia prey upon at least 28 species of fish belonging to 11 families. The characoid family Curimatidae was represented in 52%, Sciaenidae in 39% and siluriforms in 54% of the stomachs analysed (n = 29). In the dry season fish become concentrated in the main water bodies, and thus are more vulnerable to predation. During the flood period many of these fish enter the floodplain to feed, and Sotalia usually do not enter this habitat.
Marine Sotalia may penetrate up to 130 km or more upriver. The marine form probably also has a defined home range, although the area covered may be large because of the distances between one estuary or protected bay and another.
The principle limiting factor in the Amazon is the presence of rapids and small channels, where maneuverability would be restricted. The large seasonal fluctuation in river levels (10 m) influences the distribution of Sotalia: they enter lake systems during periods of high water but will leave these as the waters recede, thus avoiding entrapment in lakes that are too small or shallow. Animals may occur during the whole year in the same area. It is possible that riverine tucuxis have a limited home range, but the area of such a range is unknown.
Sotalia guianensis are found along the Caribbean and Atlantic coasts of Central and South America from Nicaragua (13?N) and possibly Honduras to Florianopolis (27?S) in southern Brazil. It has also been reported in some Caribbean islands including Trinidad and Tobago and the Abrolhos Archipelago of Brazil. One population has also been described in Maracaibo Lake, a large estuarine system located in northwestern Venezuela. Individuals from this population seem to have a smaller body size than individuals from other coastal populations, as well as some differences in the measures of a few cranial features.
Sotalia fluviatilis is found throughout the Amazon River drainage, including some of its most important tributaries, like the Putumayo and Caquetá rivers (Colombia), the Ucayali and Marañon rivers (Peru), Negro, Madeira, and Tapajos rivers (Brazil), and the Napo and Cuyabeno rivers (Ecuador).
There are no estimates of abundance for any population. The little information available on the abundance or status of Sotalia populations comes mainly from qualitative assessments in small geographical areas. These observations are already old data and are not coming from long-term observation but one time counts. For example 100-400 Sotalia guianensis dolphins were estimated 1978 near the mouth of the Magdalena river in Colombia, and noted that they were abundant in the Gulf of Cispata, near San Antero (Colombia). In Suriname, they were described as “rather common” in the mouths of the larger rivers, and in Guyana they were reported as “frequent” in the lower reaches and mouth of the Essequibo river.
A further problem is that the formerly applied method of counting animals surfacing leads often to grossly wrong results. For example Sotalia were reported to be common in the Baia de Guanabara (Rio de Janeiro), by Geise (1991) who estimated the population at 418 individuals in about 109 groups. However, more recent estimates using photo-identification only come to a number of 69-75 individuals for the same region.
In the Amazon drainage area, an average density of approximately 1.1 Sotalia fluviatilis dolphins per km of river was estimated between Manaus and Tefé in the Solimöes river. In the Iquitos area, Kasuya and Kajihara recorded 62 Sotalia during 36 hr of observations. Further upstream, Sotalia were frequently encountered in the Samiria river and its tributary the Santa Helena river. They are also common in Colombia in the Loretoyacu river, and the Tarapoto river at the El Correo Lake system and in the lower reaches of the Orinoco river.
A boat survey in 1993 estimated the abundance of the tucuxi along ca. 120 km of the Amazon River bordering Colombia, Peru, and Brazil in 409 Sotalia in the study area. Sotalia density (dolphins per km²) was highest in lakes (8.6), followed by areas along main banks (2.8) and around islands (2.0). These are among the highest densities measured to date for any cetacean
In the Cayos Miskito Reserve, Nicaragua, mean group size was 3.01. 49 Sotalia were estimated to inhabit the portions of the Reserve studied.
Threats to the Tucuxis survival:
There are no records of past or recent commercial fisheries for Sotalia. The freshwater dolphins have been protected by the superstitions of fishermen from Colombia to southern Brazil as well as in the Amazon. On the coast of Brazil Sotalia may occasionally be killed for use as bait for sharks or shrimp traps or for human consumption, although the extent of this practice is unknown. There is also a small market for the eyes and genital organs, which are used as love charms when prepared in a special manner.
Modern fishing practices and the greatly increased intensity of fishing in both the marine and freshwater habitats of this dolphin are the greatest direct threats to the species. Sotalia is easily captured in monofilament gill nets as well as in shrimp and fish traps and seine nets. Analysis of the type of fishing gear associated with the mortality of 34 Sotalia from the central Amazon revealed that 74% were caught in gill nets and 15% in seine nets. Sotalia apparently do not steal fish from nets as do Inia in the Amazon but, as they consume 14 of the 30 species of fish most exploited by man in the Amazon, incidental captures during fishing are frequent.
In Atafona (Rio de Janeiro State, Brazil) Sotalia are the dolphins most frequently caught incidentally in fisheries. Beltran (1998, in IWC, 2000) recorded 938 animals taken in drift nets from the port of Arapiranga during the summer of 1996 and a further 125 taken during the winter. These data were collected by interviewing fishermen in the port after trips and collecting carcasses. The animals were generally large and may therefore have been the marine form, but this has not yet been confirmed. The IWC sub-committee expressed its concern about the magnitude of these catches.
As the fishing activities in the mason increases overfishing takes place in many rivers. The lack of food may have negative impacts on the survival of Sotalias. Mundo Azul plans to investigate the densities of Sotalias in rivers with different fishing levels in order estimate the level of threat for dolphins.
Another potential threat to Sotalia, in both riverine and coastal environments, is the damming of rivers for hydroelectric projects, with future plans for up to 200 such dams in series along many of the main Amazon tributaries. At the very least, such dams would interrupt gene flow between Sotalia populations, creating isolated groups between dams. Furthermore, most of the migratory fish on which Sotalia feed would become extinct in the reservoirs, and the potential suitability of non-migratory fish for the diet of Sotalia is unknown.
Pollution from industrial, mining and agricultural activities may be considered a threat both directly, through the destruction of habitat, or indirectly, through contamination of the food chain. Large harbours like the Baia de Guanabara (Rio de Janiero) and Santos (São Paulo) are extremely polluted with effluent, including heavy metals, posing a serious potential threat. The continued use of insecticides containing substances banned elsewhere is common in South America. Mercury is used in the refining of fluvial gold and then, like the pesticides, probably enters the aquatic food chain of the rivers. Mercury and selenium were found in the livers of two Sotalia from Suriname. Exploration for oil in the offshore regions of Brazil, Venezuela and Colombia may not pose a direct threat to Sotalia. Nevertheless, the apparent dependence of this dolphin on estuaries means that an oil spill near such an area could contaminate the food chain and affect local populations.
Whale watching and conservation initiatives:
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What we do to stop the dolphin slaughter in Peru:
According to our estimate between 5000 and 15000 dolphins are killed illegally in Peru each year to be used as shark bait by Peruvian fishermen. Additionally up to 3000 dolphins are killed each year illegally in Peru for human consumption. In 2002 Mundo Azul started investigating the Peruvian black market on illegally caught dolphin meat. The dolphin meat is regularly landed at night on beaches near the ports in order to avoid the controls of harbor officials. At this point, the meat is already cut into small pieces and hidden in boxes, while heads, flukes, bones and intestines have been thrown over board before or while entering the harbor. The meat is then openly sold on local markets. In 2013 Mundo Azul uncovered the massive dolphin kill for shark bait. Stefan Austermühle, Executive Director of Mundo Azul, managed to travel in a full month fishing trip and filmed the brutal killing of dolphins – pictures that sent a shock wave around the world. Please support our campaign to pressure the Peruvian government to act decisively in order to end the dolphin killing in Peru.
Mundo Azuls volunteers are engaged in undercover investigation of illegal sales of dolphin meat. We are then providing the collected intelligence to the Peruvian police and are actively supporting the implementation of police raids. We are also supporting the Peruvian police thru capacity building. Raising public awareness and environmental education are further activities of our dolphin conservation campaign. We are engaged in dolphin research providing us with important baseline information for conservation planning. Finally we are promoting whale and dolphin watching as a sustainable economic alternative to illegal dolphin killing.
We are also active on an international level against dolphin captivity and whaling.
What you can do to stop the dolphin slaughter in Peru
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