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Amazon River Dolphin
An Amazon River Dolphin at Duisburg Zoo.
Size comparison against an average human
Conservation status
Vulnerable (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Subclass:	Eutheria
Order:	Cetacea
Suborder:	Odontoceti
Superfamily:	Platanistoidea
Family:	Iniidae Gray, 1846
Genus:	Inia
Species:	I. geoffrensis
Binomial name
Inia geoffrensis Blainville, 1817
Amazon River Dolphin range

Origin

Location

The Amazon River Dolphin (Inia geoffrensis) is a freshwater river dolphin endemic to the Orinoco, Amazon and Araguaia/Tocantins River systems. The largest of the river dolphins, this species is not to be confused with the Tucuxi (Sotalia fluviatilis), whose range overlaps that of the Amazon River Dolphin but is not a true river dolphin. The IUCN lists various other names to describe this species including Amazon Dolphin, Boto Vermelho, Boto Cor-de-Rosa, Bouto, Bufeo, Dauphin de l'Amazone, Inia, Pink Dolphin, Wee Quacker, Pink Freshwater Dolphin, Pink Porpoise, Encantado, and Tonina. It is also called Bufeo Colorado, Boto, Boutu, Nay, and Pink River Dolphin (14).

Habitat

The Boto dolphin lives only in freshwater, both clear and muddy. The temperature range of the water is from 73-86 degrees Fahrenheit (9). “The species is found in a variety of riverine habitat types, including rivers, small channels and lakes. Concentrations occur mainly at the mouth of rivers, below rapids and smaller channels running parallel to the main river.” The dolphins also use the flooded forests and grasslands as habitat during the flood season (3). The flood season starts in December and lasts until June. “Water levels peak in May and June and reach their lowest levels between September and early November (9).”

Taxonomy

The species was described by Henri Marie Ducrotay de Blainville in 1817. 1998 classification lists a single species, I. geoffrensis, in the genus Inia, with three recognized subspecies:

• I.g. geoffrensis - Amazon and Araguaia/Tocantins basin population (excluding Madeira River drainage area, upstream of the Teotonio Rapids in Rondonia)
• I.g. boliviensis - Amazon basin (Bolivian sub-basin) population in the Madeira drainage area in Bolivia upstream of the Teotonio Rapids
• I.g. humboldtiana - Orinoco basin population

Some older classifications listed the boliviensis population as a separate species.

Evolution and Anatomy

Evolution

File:Hamilton etal 2001 fig3-thumb.png

Figure 1. Evolution of River Dolphins (6).

The ancestors of the Boto seemed to be a successful marine group, but they were displaced in the Miocene period. It is believed that the displacement occurred because more advanced delphinids had established. Scientists hypothesized that the Inia entered the Amazon from the Atlantic Ocean 1.8-5 million years ago, or from the Pacific Ocean about 15 million years ago (8).

Anatomy

There is sexual dimorphism in Amazon River Dolphins. This means that the males are generally larger than the females. “This distinction implies long evolutionary separation and fundamental differences in social behavior (1).” Adult females weigh 180-260 pounds while adult males weigh 260-400 pounds. The average length for these adult dolphins is 6.5-8.5 feet long (9).

Adults are usually pink in color on their ventral sides and flanks while juveniles are a gray color. The degree of pink coloring varies by individual. Males seem to appear pinker than females (this is a sexual dimorphism factor) (1). Capillaries near the skin surface account for this coloration. There may be other factors to influence the pink coloring besides their age such as temperature and chemical nature (particularly percentage of iron content) within the water (8). This species has a prominent forehead, small eyes, and a long beak. Their beaks have 24-34 conical and molar-like teeth. “The conical teeth in the front of the mouth are used for holding prey; the molars in the rear of the mouth are used to grind food before swallowing (7).” There are stiff hairs on its beak throughout its entire life; this is unique compared to other dolphin species. These hairs are used for sensory reasons (10).

The Boto has a low, long dorsal fin. Their flukes are broad and triangular. Its flippers are large, broad, and paddle-like. It is predicted that they are this way to help them maneuver through shallow water (3). The dolphin has unfused vertebrae in its neck which allows it to move its head to a 90 degree angle. This is an adaptation for feeding and moving in between the trees of the flooded forests (2).

Human-Dolphin Relationship

Mythology

In Amazonian cultures, there are supernatural beings that protect the forests and waters. The Boto dolphin is one of these beings; it is one of the most powerful and widely known beings. The dolphin is viewed as mischievous and tempestuous by the indigenous people, and because of this, it is both feared and respected. There are many legends associated with these beliefs (5).

There are two main folklores in the Amazon relating the Boto dolphin to sexual encounters. One of these myths is that the dolphins transform into Caucasian men at nightfall to perform dances in order to seduce women. They are also believed to enter houses, and other areas, to paralyze women so that they can have intercourse with them. Many teenage pregnancies are blamed on the dolphin. Before daylight, they transform back into the Amazon River Dolphin. This dolphin shapeshifter is called an encantado. It has been suggested that the myths arose partly because dolphin genitalia bear a resemblance to that of humans. The myths may have also arisen due to the belief that the spirits of those who have drowned enter the bodies of the dolphins. That is why they can transform into men (5).

In local areas, there are also tales that it is bad luck to kill these dolphins. Legend also states that if a person makes eye contact with an Amazon River Dolphin, that person will have nightmares for the rest of his or her life. These myths have served as a source of protection for the species (5).

Human Uses

Associated with the legends of the Boto is a culture with the use of various fetishes particularly for dried eyeballs and genitalia. The use of these fetishes may or may not be accompanied by the intervention of a priest. These fetishes are not supported by the indigenous peoples; the demands for body parts of the dolphin are mostly from city-dwellers in the Amazon, coastal regions of northern and northeastern Brazil. These areas do not have the same folklore as those that live by the dolphin, so they do not follow the taboos. The start of these fetishes occurred when Old World diseases and Portuguese slave raids occurred in the Amazon. These events depopulated the Amazon allowing impoverished peoples from north and northeastern parts of Brazil to migrate into the Amazon area. The people from those areas had a strong belief in “love magic”. They used both plants and animals to make amulets and other solutions for magic. It is proposed that when the migrants heard about the Boto’s legends, they thought it would be a good source for love magic ingredients. Although Boto objects are sold today, a recent study has shown that despite the claim of the seller and the belief of the buyers, none of the body parts are derived from the Boto. They are derived from Sotalia guianensis which are most likely harvested along the coast and the Amazon River delta. They are then traded up the Amazon River. In inland cities that are far from the coast, many if not most of the fetish products are derived from domestic animals such as sheep and pigs (5).

Value

The Amazon River Dolphin has value to humans and its environment. The species has both non-market and market values. The Boto provides cultural value, recreational value, and scientific discovery. The native peoples view this dolphin as a spiritual being. It is highly respected by them, and greatly influences their culture (5). The species also influences humans by providing educational experiences and scientific discoveries. The research done on the Boto not only reflects that specific species, but also how other species interact and how the whole ecosystem functions. People also relate the Boto dolphin to artistic value and aesthetic value. Recreational value is also important to people with this species. Although aggressive at times, the dolphin is primarily a very social and playful creature (8). These playful mannerisms attract attention to the species. This attention can result in ecotourism opportunities. The Boto also provides market value, but this value is very little. The dolphin is only sold if accidental death occurs from human impacts; only then is the Boto sold to the consumer’s market (3, 5).

Threats

Natural Threats

There are no known natural predators to the Amazon River Dolphin. Despite this, there are some natural threats posed. Due to the reproduction (low count offspring) and maturity (high age) rates, this species is at risk (9). The specifics of these can be seen below in the Behavior: Reproduction and Sexuality section. The vulnerability of the species, from these rates, is heightened by human threats which are currently depleting the species’ population. The rate at which the species reproduces and matures may not be able to cope with impending pressures.

Human Threats

As the human population grows in the Amazon, the Boto dolphin becomes more vulnerable. There are various threats that humans impose. Some of these threats are direct catch, incidental catch, deliberate killings, over-fishing, habitat degradation, and pollution (3).

Direct catch infers that parts of stranded or incidentally caught dolphins may be sold as love charms. In Bolivia, it has been reported that rifles and nets are used to capture the Boto. In the Central Amazon, this is not done. There are very few catches there, and the catches are mostly all incidental. Only a very small number of these are used for commercial purposes. People in the Colombian Amazon kill the dolphins with guns, harpoons, and poisons “to deter gear interactions.” The Orinoco and Peruvian Amazon kill the dolphins when there are interactions with the fisheries (3).

Incidental catch often occurs as a result of entanglement in fishing nets as well as collisions with outboard motors. By-catch is another problem. There are no recorded numbers on incidental catches, so the magnitude at which this affects the dolphins is not known. Despite this, fishing efforts have been increasing in some areas within the past years; this may be putting a greater stress on the dolphin from incidental catches. The nets primarily causing the deaths of these dolphins are drift gillnets, fixed gillnets, and lampara seine nets. Also, there are deaths associated with illegal fishing methods, such as explosives. Overall incidental deaths are seasonal and are different throughout the different areas in the basin. “There are no estimates of total incidental mortality, and all accounts are anecdotal (3).”

Deliberate killings are done by fishermen because the dolphins have learned to utilize the fishermen’s gear to harvest fish for themselves. This not only reduces the fishermen’s yield significantly, but it also may damage their gear (3).

Over-fishing is due to the use of nylon nets, which contribute to incidental deaths. Nylon nets are highly efficient at catching fish; this efficiency creates a pressure on the fisheries overall populations. With this increasing pressure, Boto-human interactions are increasing. Despite the pressures from the dwindling fish populations, the Boto dolphin is little affected by it. “Dietary analysis has shown that only 43% of 53 identified prey species are of commercial value and that the dolphins generally prey on size-classes of fish below those of commercial interest (3).”

Habitat degradation is a threat to the Amazon River Dolphin. Habitat degradation is due to human population growth. These population increases result in deforestation, increased agricultural land, increased cattle ranching, the establishment of plantations, and the development of other industries (3). One major concern is hydroelectric development. Hydroelectric development has been fragmenting Boto populations. Currently, there are ten major dams in the Amazon Basin that are isolating dolphins upstream. Not only do these dams cause fragmentation, but they also change sediment flows, hydraulic flows, and the water quality of rivers. Dams eliminate many essential qualities of downstream flows such as the flow of sediment. This flow of sediment is crucial because it is what creates sandbars and islands within the basin. Dams also change the fish populations. The fish populations change because hydraulic flow changes. When flooding season occurs, the river will not flow in the same manner. Much of the water before the dam will flood out onto adjacent floodplains. These areas are not suitable habitat for the fish within the river. Also, “the number of ecological niches available for supporting diverse communities of riverine biota is reduced.” This is because dams change the atmosphere of the environment. The dams alter the water’s flow, temperature, and detritus loading. These elements are essential to certain organisms within the basin (9).

Pollution is another threat to the Boto dolphin. There is a significant increase in pesticide use due to the increase in agricultural land. These pesticides can runoff into the water altering its quality. There is pollution entering the basin from heavy metals. These metals are from the mining of gold and the indiscriminate use of mercury. Pulp mills are another source of pollution (3).

Behavior

Social

The Amazon River Dolphin is a solitary species (4). Sometimes the dolphins are seen in pairs. If seen in pairs, it is usually because it is a mother and a calf together. (The mother and the calf stay together for about 2.5 years (9).) Sometimes, during feeding, loose groups are established. This dolphin is sometimes a very playful creature which interacts with the native peoples. (Sometimes however, just like any creature, they may become aggressive.) Their degree of curiosity varies within the individual, but there are many reported events where the dolphins are not afraid of boats. It has even been said that dolphins may grab boat oars or go right up next to the boats. There have also been reports of the dolphins pushing humans to shore after canoes capsized (8).

Sexual Dimorphism

There is sexual dimorphism in this species. Males are larger than females, and males appear to be pinker in color than females. Also, males appear to have more scars than females and more life threatening injuries. There are main apparent areas for injuries. These areas are the trailing edges of flukes and pectoral fins and the blowhole. “The raised areas around the blowhole became depigmented and damaged due to repeated biting and abrasion. The trailing edges of the pectoral fins and flukes became progressively serrated as pieces were removed (Figure 2).” Some males have modified tissue that may either be scar tissue or genetic tissue used as a defense. This indicates that there is competition for a resource. Since it is apparent that this competition has male-male aggression, it is predicted that this resource is mating opportunities (1).

File:Tf1

“Figure 2. Intraspecific wounds and abrasion on male Botos. (Top left) typical depigmentation pattern on raised areas around the blowhole; (top right) less advanced case with fresh wounds; (bottom) ventral surface of flukes, showing distal portions missing on both sides.”

Reproduction and Sexuality

Females become sexually mature at proximately 5.3-5.7 feet in length while males are mature at about 6.5 feet in length. Females generally do not have offspring until approximately 6-10 years of age (9). Male competition for mating opportunities does seem to be apparent as stated in “sexual dimorphism” above (1). Although mating occurs often, pregnancy does not always result. The annual rate of pregnancy in mature females is about 10-15%. When pregnant, gestation is about 11 months long. Calving occurs in May, June and July due to the timing of peak and declining water levels. This season is necessary for the mother because she needs to be able to provide an ample amount of food for herself (9). Offspring count is usually only one calf. Calves are generally 32 inches long at birth and weigh about 15 pounds (8). The calf stays with the mother for about 2.5 years. (This is basically the only time this species is seen in pairs.) Lactation occurs for at least a year during this time period. After giving birth, the female will not reproduce for about 4-5 years (9).

Feeding

The Boto feed on a large variety of fish of over 50 species. They usually only eat fish up to one foot in length. Botos also consume a number of turtles and crustaceans. They are able to eat these hard shelled creatures because their rear teeth are flat with peaks and cusps that are perfect for crushing. The dolphin eats about 6-10 pounds of food a day. Their diet changes in accordance with seasonal changes because there are flood cycles enabling access to different foods. Feeding is usually done in the flooded forest, close to shore, shallow bays, or where two rivers meet. Many times feeding is solitary, but there are some instances in which feeding takes place in groups (9). Sometimes they even feed with tucuxi. They are well adapted to feeding in their waters because they can rotate their head 90 degrees, downward or sideways, and they also have stiff hairs on their beaks. The dolphins are able to rotate their heads 90 degrees because their necks have unfused vertebrae. This adaptation is very important when swimming in areas of the flooded forest because the dolphin needs to be able to get around roots to obtain its food (7). The stiff hairs on the dolphins’ beaks help sense, by touch, to find food on the floor of the river, such as crustaceans (10).

Senses

Although the Amazon River Dolphin’s eyes appear to be small, they are actually as large as those in marine systems. This species’ eyes are in its skull. So, this dolphin can actually see very well. But, the dolphin has large cheeks which interfere with its view. To overcome this, the dolphins swim upside down to look down (9). The species’ eyesight is only important in clear waters. In muddy waters, the Boto uses sonar and sensory bristles on its beak to navigate and search for food (10).

Vocalizations

It is known that the Boto has vocalizations, but little information is known about the behavior associated with these vocalizations because people did not document their findings. Vocalizations are diverse; they are used to navigate, communicate, and orientate the species. Vocalizations vary between populations and species. A recent study was performed in the central Brazilian Amazon, over a five week period, to analyze vocalizations for the Amazon River Dolphin. The scientists “monitored and recorded the vocalizations, noted group size and activity, and tallied frequencies of breathing and pre-diving surfaces.” Many diverse sounds were recorded during the study. There was one distinct low frequency sound that only was present when the Boto was present. This information, that the sound was distinct to only the Inia, is nearly certain because when individuals passed under the boat, the sounds were heard shifting in the corresponding direction and timing. Also, the amplitude corresponded to the location of the individuals. There is also evidence that this information is true because only when the Boto was actually present were the distinctive sounds made. Overall, there were no whistles heard from the Boto. (Whistles are usually heard from delphinid dolphins.) The frequency range of vocalizations did not generally exceed 5 kHz. There showed to be diversity in vocalization structure. There was diversity in temporal, frequency, and harmonic features. Two hundred forty vocalizations were analyzed in the study, and 216 of the 240 contained multiple notes. The group sizes of the dolphins ranged from 1-14 individuals. “Across all observation blocks, vocal activity correlated positively with group size and with both types of surfacing activity.” “Overall, Inia vocal output correlated positively with pre-diving surfaces, suggesting that vocalizations are associated with feeding (11).”

Conservation Problems

Conservation projects and management of fisheries in Latin America have “been hampered” because of political and socio-economic issues. Due to these conflicts, there is little commitment to conservation, a lack of education and awareness of the environment, and insufficient scientific knowledge on some environmental subjects. Recently, many local and regional areas have tried to conserve the environment and protect species, but they are “limited in scale and scope.” “The need is urgent to identify the most critical and immediate conservation problems for each nation and each species or population. Priority should be placed on (1) preventing the extinction of species, subspecies, and populations; (2) beginning or continuing studies of the biology, ecology, and population dynamics of these mammals as a basis for their conservation and informed management; (3) formulation or improvement of national policies dealing with the conservation of aquatic mammals and other renewable resources; and (4) promoting regional agreements and long-term international programs for the study and conservation of renewable resources (12).”

References

1) A. R. Martin, and V.M.F. Da Silva "Sexual Dimorphism and Body Scarring in the Boto (Amazon River Dolphin) Inia Geoffrensis." Marine Mammal Science. 22.1 (January 10 2006): 25-33.

2) American Cetacean Society. "BOTO (Amazon River Dolphin)" 10 Nov. 2008. <http://www.acsonline.org/factpack/Boto.htm>.

3) CMS. "Whales and Dolphins Inia geoffrensis (de Blainville, 1817)" 11 Nov. 2008. <http://www.cms.int/reports/small_cetaceans/data/I_geoffrensis/I_geoffrensis.h tm>.

4) E. O. Boede, E. Mujica-Jorquera, N. De Boede "Management of the Amazon River dolphin Inia geoffrensis at Valencia Aquarium, Venezuela." International Zoo Yearbook. 36.1 (January 1998): 214-222.

5) Gravena, Waleska, Hrbek, Tomas, M.F. Vera da Silva, Farias, Izeni P. "Amazon River dolphin love fetishes: From folklore to molecular forensics." Marine Mammal Science. 24.4 (October 2008): 969-978. 6) Hamilton, Healy, et al. "Evolution of River Dolphins." The Royal Society. 2001. 552.

7) Inia geoffrensis, Amazon River Dolphin - MarineBio.org. Retrieved Tuesday, November 11, 2008, from http://marinebio.org/species.asp?id=337.

8)International Society for the Preservation of the Tropical Rainforest. "Pink and Gray River Dolphins." 4 Dec. 2008. <http://www.isptr-pard.org/dolphin.html>.

9) Massicot, Paul. "Animal Info - Boto (Amazon River Dolphin)" 10 Nov. 2008. <http://www.animalinfo.org/species/cetacean/iniageof.htm>.

10) McQuire, Tamara. "About the Dolphins." Virtual Explorers. 11 Nov. 2008. <http://www.virtualexplorers.org/ARD/Dolphin/bkgd.htm>.

11) Podos, Jefferey, M.F. Vera da Silva, Rossi-Santos, Marcos R. "Vocalizations of Amazon River Dolphins, Inia geoffrensis: Insights into the Evolutionary Origins of Delphinid Whistles." Ethology. 108.7 (July 2002): 601-612.

12) Vidal, Omar. "Aquatic Mammal Conservation in Latin America: Problems and Perspectives." Conservation Biology. 7.4 (December 1993): 788-795.

13) "Whales and Dolphins" at ancientspiral.com

14) "Wildfacts: Boto". BBC. Retrieved on 2007-02-21.

General references

• Cetacean Specialist Group (1996). Inia geoffrensis. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes a lengthy justification of why this species is vulnerable.
• Rice, Dale W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. 231 pp.
• Montgomery, Sy (2000). Journey of the pink dolphins : an Amazon quest. Simon & Schuster, 317 pages. 068484558X
• Juliet Clutton-Brock (2000). Mammals, 381 pages.
• Hilda. "Pink Dolphin". Retrieved 2007-09-08.

External links

• Book: "Pink dolphin, friend of the river" (Web Site - English & Spanish)
• Omacha Foundation - A non-government and non-profit organisation, created to study, research and protect river dolphins and other fauna and aquatic ecosystems in Colombia (website in English and Spanish). Winner of the 2007 Whitley Awards (UK)
• Projeto Boto - a non-profit research project that is increasing knowledge, understanding and the conservation prospects of the Amazon's two endemic dolphins - the Amazon River Dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis)
• Dolphins, Whales and Porpoises: 2002–2010 Conservation Action Plan for the World's Cetaceans. IUCN/SSC Cetacean Specialist Group 2003, Reeves et al. HTML copy of book-length report
• Convention on Migratory Species page on the Amazon Dolphin
• The Nature Conservancy works to protect habitat for the Amazon River Dolphin
• Walker's Mammals of the World Online - Amazon Dolphins
• Animal Info page on the Amazon River Dolphin
• - Virtual Explorers
• Whale & Dolphin Conservation Society (WDCS)
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