Amazon River Dolphin
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lnia geoffrensis (De Blainville, 1817)
English = Amazon river dolphin Spanish = Delfin rosado
Conservation status of the Amazon river dolphin:
- Amazon river dolphins are listed in Annex 2 of Convention on International Trade in Endangered Species;
- Amazon river dolphins are listed in Annex C1 (strongest category of protection) of Regulation 3626/82 of the European Union;
- Amazon river dolphins are protected by the Marine Mammal Protection Act of the United States of America;
- Amazon river dolphins are listed as “vulnerable” by the International Union for Conservation of Nature and Natural Resources,
- Amazon river dolphins are protected in Peru since 1990 by Ministerial ordenance and since 1996 by national law
Distribution of the Amazon river dolphin in Peru:
Amazon (Rivers: Putumayo, Napo, Tigre, Marañon, Huallaga, Ucayali, Amazonas)
Present threats for the Amazon river dolphin:
- hydroelectric development
- pollution from agriculture, industry and mining
The genus name “Inia” is the Guarayo Indian word for “dolphin”; the species name (“geoffrensis“) – named for Geoffrey St. Hilaire, “who plundered the first zoological specimens from Portugal for Napoleon Bonaparte”.
The Amazon River dolphin or boto is the largest species of the river dolphin family, weighting up to 180 kg (400 lb) with a length up to 2.6 m (8.5′). Most adult Amazon river dolphins are pink, although some have a darker back or are partially gray.
Length: 2 – 2.6 m (6.5 – 8.5′); Weight: females: 80 – 120 kg (180 – 260 lb); males: 120 – 180 kg (260 – 400 lb)
Although the Amazon river dolphin’s eyes appear small and inconspicuous, they are actually, in the skull, as large as those of marine dolphins. Thus the Amazon river dolphin can see well. On the other hand, it can also rely on its sonar as it swims through a murky flooded forest. Utilizing its flexible neck, as it swims, a Amazon river dolphin turns its head from side to side, sounding its way through the maze of drowned branches with a series of pulsed clicks at frequencies up to 170 kilohertz. Its bulbous forehead ends in a long, tube-shaped beak bearing sensory bristles that allow it to feel for food in a river’s depths.
The pectoral fins are broad and paddle-like; the flukes are broad and triangular; and it lacks a prominent dorsal fin, possessing instead a low ridge along the back. It is believed that the boto’s pink color comes from capillaries close to the surface of the skin that give it a rosy flush.
The Amazon river dolphin occurs throughout much of the Amazon and Orinoco watersheds, being found almost everywhere it can physically reach without venturing into marine waters. The principal limits to its distribution seem to be impassable rapids, waterfalls, and very small or shallow rivers.
Its current distribution may be little different from that in pre-colonial settlement times: in the Orinoco River system, including the Apure and Meta Rivers, upstream as far as the rapids at Puerto Ayacucho; and throughout most of the Amazon basin (below an elevation of about 100 m (330′)) plus the upper Rio Madeira drainage (above the Teotonio rapids) in Bolivia, where it is confined to the Rio Mamoré and its main branch the Rio Iténez (= Rio Guaporé), including lower reaches of their larger tributaries (at an elevation of 100 – 300 m (330 – 990′)). It is found at water temperatures from 23 – 30 deg C (73 – 86 deg F).
Countries where the boto is currently found: Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela. (Amazon and Orinoco River basins)
The Amazon river dolphin has benefited in many parts of the Amazon from legends that associate it with supernatural powers. It is believed that the spirits of drowned persons enter the bodies of botos, and that these animals change into handsome young men. Consequently there has been no direct hunting of the Amazon river dolphin.
There are no current population estimates for the Amazon River dolphins in Peru. The latest counts in some rivers within the protected area are from the mid-nineties and might not be valid anymore. Therefore Mundo Azul plans to launch a long term population study of Amazon River dolphins and Tucuxis (the second dolphin species in the Amazon basin). We will be using photo-identification and transect counts. Only if we know the actual population and their trends in different rivers we can design specific conservation strategies and initiate programs with the local people. The study will be volunteer-based.
Age of females at first birth is estimated to be between 6 – 10 years. Females become sexually mature between 1.6 – 1.8 m (5.3 – 5.7′) in length. Males appear to reach sexual maturity at body lengths over 2.0 m (6.5′).
The gestation period of the Amazon river dolphin is estimated at about 11 months. Calving occurs during the months of May, June, and July, coincident with peak river levels and their initial decline at the start of the dry season. This seasonality means that the female Amazon river dolphin’s high energy demands near birth and during early lactation are met by increased availability of fish driven from flooded forests by falling water levels and forced back into, and concentrated in, the remaining waterways.
Females give birth to a single calf. Inter-birth intervals are typically 4 – 5 years. The annual pregnancy rate of mature females is around 10 – 15%.
Lactation appears to be prolonged (well over a year). Mother and offspring stay together for at least 2.5 years. Longevity is probably about 30 years.
The Amazon river dolphin is a generalist feeder. Its diet is known to include over 50 species of fish, usually less than 30 cm (1′) long, as well as freshwater crabs and river turtles. Its diet varies markedly on a seasonal basis in synchrony with the flood cycle. Its front teeth are peglike, for seizing prey, but the rear teeth are flatter with peaks or cusps, and thus suited to crushing freshwater crabs, river turtles, and armored catfish. Stomach content analysis showed that less than half the fish species the boto eats are commercially important, and these are taken in relatively small quantities. The boto eats 2.7 – 4.5 kg (6 – 10 lb) of fish each day. Feeding is usually done close to shore, in shallow bays, in flooded forests, or where two rivers meet. Although often a solitary feeder, the Amazon river dolphin forms loose groups that cooperate in herding and attacking schools of fish.
The Amazon river dolphin’s activity is more intense during early morning and late afternoon, when significant movement into lakes from the river has been noted. Weather conditions affect activity, with more Amazon river dolphins in evidence on cloudy or rainy days. It apparently is non-migratory, in that regular long journeys do not appear to be undertaken.
The Amazon river dolphin uses fresh waters of all types as habitat but is not found in estuaries or other saline waters. It appears to favor areas such as confluences, sharp bends, and sandbars. In the central Amazon basin, large changes in water levels affect the local distribution of botos. A significant increase in water level during the flood season leads to the inundation of large areas of forest. Amazon river dolphins move out of the main river into channels and small lakes and then into the forest itself, swimming among the trees, as the rising waters flood the forest.
The Amazon river dolphin readily associates with man and is playful, sometimes retrieving thrown objects and even soliciting physical contact. When swimming, Amazon river dolphins may nip divers, play tag or take the diver’s hand under its flipper and tow him or embrace him. Wild Amazon river dolphins grasp fishermen’s paddles, rub against canoes, and may become quite tame.
The Amazon river dolphins dives usually last less than 1 – 2 minutes, but they can last up to 4 minutes. Amazon river dolphins surface very briefly, rarely twice in quick succession, and almost never in a predictable position.
As is typical for river dolphins, the Amazon river dolphin is predominantly solitary, with only 12 – 26% of sightings involving pairs. Larger groups are occasionally seen; e.g., loose aggregations have been observed at feeding areas. Most groups of two are apparently mothers and calves. There do not seem to be seasonal differences in group size.
Estimates of up to 25 individuals/sq km (65 individuals/sq mi) have been made during the dry season when animals are aggregated in the channels. In a study in the Peruvian Amazon, the densities of the Amazon river dolphin in confluence areas were found to be much greater (by two to six times) than the overall density in the entire river. This was the case for all of the water levels that were sampled (river flows ranging from medium-low to high).
Densities of Amazon river dolphins reported from several surveys:
0.28 individuals/km (0.44 individuals/mi) in a 1200 km (744 mi) section of the Amazon River between Manaus and Santo Antonio de Ica
0.25 individuals/km (0.4 individuals/mi) over 130 km (81 mi) on Rio Ichilo
1.1 individuals/km (1.8 individuals/mi) on Rio Ipurupuru, and
1.0 individuals/ km (1.6 individuals/mi) on Rio Ibare
1.12 individuals/km (1.8 individuals/mi). (Tijamuchi River, in Bolivia)
tributaries: 4.8 individuals/sq km (12.5 individuals/sq mi); areas around islands: 2.7 individuals/sq km (7.0 individuals/sq mi); along main banks: 2.0 individuals/sq km (5.2 individuals/sq mi) (along 120 km of the Amazon River bordering Brazil, Colombia, and Peru)
Threats for the Amazon river dolphin:
The Amazon river dolphin is vulnerable to human-induced habitat changes and suffers some incidental mortality in fisheries, but it has not yet been depleted to anything like the extent of its Asian counterparts, such as the baiji, the Ganges river dolphin, and the Indus river dolphin. Threats include bycatch in fisheries; hydroelectric development; deforestation; and pollution from agriculture, industry and mining.
Interactions with fisheries:
Although there is no regular hunt for Amazon river dolphins, they are sometimes killed and maimed deliberately by fishermen to protect their catch and gear, or in retaliation for perceived competition for fish resources.
In the Orinoco, fishing of Silver Dollar or Palometa (Mylossoma sp.) has caused conflicts between fisheries and Amazon river dolphins. To capture this species, fishers first clear vegetation from plains alongside riparian forests, then when water levels rise, they throw maize into the water for a period of 5 to 20 days to attract large quantities of Palometas. The fish are subsequently caught using rods and hooks. Some 200 kg of Palometa can be taken using this method. The fish are generally sold in Venezuela.
Over the last five years, fishers have reported that during this process, groups of more than four dolphins appear in these areas, attacking the Palometas and causing economic losses. Faced with this situation, fishers have shot or harpooned the Amazon river dolphins to prevent further loss of fish.
In the Amazon and Orinoco rivers, fishing has begun of the carrion-feeding Vulture Catfish (Calophysus macropterus) known as Mapurito in the Orinoco region and Mota or Simí in the Amazon. The fish is caught using dolphin meat as bait. Formerly, pig’s innards or viscera from other animals were used to capture the Vulture Catfish, but this practice has now been replaced by the use of threatened species such as Amazon river dolphins or caimans.
Fishing of this species is mainly carried out in Brazil, where several estates are involved in the fishing, sale and distribution of Vulture Catfish. Actors in the commercial chain include bait hunters and fishers as well as storage facilities supplying shipping vessels which transport the fish to Leticia from where it is sent to Bogotá and other cities within Colombia.
In the Orinoco region, those catching Vulture Catfish (Pimelodus grosskopfii) are known as guareros and are responsible for obtaining Amazon river dolphins, caimans or pigs used as bait (either captured or bought). The ease and efficiency of catching Vulture Catfish due to a plentiful supply of bait (dolphins and caimans) has led to increased interest in the consumption of the species in recent years.
In Peru, Bolivia, Colombia and Brazil, one of the main causes is bycatch. Even though many Amazon river dolphins are freed from the nets by the fishermen themselves, many are left to die or are killed with machetes. Their meat is than used as bait for fish. In the National Reserve of Pacaya-Samiria, where commercial fisheries is a problem, dolphins have been reported to be poisoned with Methil-paration.
There are 10 major dams at present in the Amazon basin, of which 8 have isolated boto populations upstream. Some of these dams have, therefore, fragmented the population, but these fragments are still probably quite large. Dam construction and operation cause major changes in the flow regime, sediment load, and water quality of rivers. Dams eliminate many of the dynamic attributes of downstream waters and block the flow-through of sediment essential to the formation of islands and sandbars. Downstream flows are normally not allowed to overspill riverbanks onto adjacent floodplains. As a result, fish production decreases dramatically. Natural fluctuations in flow, temperature, and detritus loading, which provide optimal conditions for a large number of aquatic organisms, are suppressed by dams, and the number of ecological niches available for supporting diverse communities of riverine biota is reduced.
The main alterations to ecosystems from this type of project are:
Changes to physical and chemical properties of the water, especially the reduction of oxygen and the increase of sulphuric acid which can cause fish mortality.
Pollution due to pesticides (organochlorine compounds) used in agriculture; heavy metals such as mercury used in gold extraction; and other elements used in the paper industry (nitrogen, phosphorus, chlorine, aluminium, barium, calcium, iron, potassium, magnesium, sodium and silicon).
Reduction in a large variety of fish species making up part of the Amazon river dolphins’ diet.
Destruction and fragmentation of key habitats for many species.
The oil industry threatens the Amazon and Orinoco basins. In Colombia, armed groups have blown up oil pipelines, causing serious damage. The Caño Limón oil pipeline (running from Arauca to Bolívar) has been subject to 473 attacks since it was built. The resulting 1.5m barrels of spilt petroleum have caused irreparable pollution to aquatic ecosystems. In total, these oil spills are among the six largest in history and the largest of any in continental waters. The principal problems associated with the petroleum industry are as follows:
Construction of new roads for petroleum exploration.
Increase in human settlements and expansion of agricultural frontiers
Whale watching and conservation initiatives:
Whale and dolphin watching offers an economic alternative to whaling and support species conservation. Whale watching tours are also offering research opportunities. Support species conservation and research, while enjoying whales and dolphins in Peru with Nature Expeditions.
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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.
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