Amazon river dolphin

The Amazon river dolphin (Inia geoffrensis), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale endemic to South America and is classified in the family Iniidae. Three subspecies are currently recognized: I. g. geoffrensis (Amazon river dolphin), I. g. boliviensis (Bolivian river dolphin) and I. g. humboldtiana (Orinoco river dolphin). The position of the Araguaian river dolphin (I. araguaiaensis) within the clade is still unclear. The three subspecies are distributed in the Amazon basin, the upper Madeira River in Bolivia, and the Orinoco basin, respectively. The Amazon river dolphin is the largest species of river dolphin, with many adult males reaching 1...

The Amazon river dolphin are commonly seen singly or in pairs, but may also occur in pods that rarely contain more than eight individuals. Pods as large as 37 individuals have been seen in the Amazon, but the average is three. In the Orinoco, the largest observed groups number 30, but the average is just above five. During prey time, as many as 35 pink dolphins work together to obtain their prey. Typically, social bonds occur between mother and child, but may also been seen in heterogeneous groups or bachelor groups. The largest congregations are seen in areas with abundant food, and at the mouths of rivers. There is significant segregation during the rainy season, with males occupying the river channels, while females and their offspring are located in flooded areas. However, in the dry season, there is no such separation. Due to the high level of prey fish, larger group-sizes are seen in large sections that are directly influenced by whitewater (such as main rivers and lakes, especially during low water season) than in smaller sections influenced by blackwater (such as channels and smaller tributaries). In their freshwater habitat they are apex predators and gatherings depend more on food sources and habitat availability than in oceanic dolphins where protection from larger predators is necessary. Captive studies have shown that the Amazon river dolphin is less shy than the bottlenose dolphin, but also less sociable. It is very curious and has a remarkable lack of fear of foreign objects. However, dolphins in captivity may not show the same behavior that they do in their natural environment, where they have been reported to hold the oars of fishermen, rub against boats, pluck underwater plants, and play with sticks, logs, clay, turtles, snakes, and fish. They are slow swimmers; they commonly travel at speeds of 1.5 to 3.2 kilometres per hour (0.93 to 1.99 mph) but have been recorded to swim at speeds up to 14 to 22 kilometres per hour (8.7 to 13.7 mph). When they surface, the tips of the snout, melon and dorsal fins appear simultaneously, the tail rarely showing before diving. They can also shake their fins, and pull their tail fin and head above the water to observe the environment. They occasionally jump out of the water, sometimes as high as a meter (3.14 ft). They are harder to train than most other species of dolphin.

Ecuador

The diet of the Amazon river dolphin is the most diverse of the toothed whales. It consists of at least 53 different species of fish, grouped in 19 families. The prey size is between 5 and 80 centimetres (2.0 and 31.5 in), with an average of 20 centimetres (7.9 in). The most frequently consumed fish belong to the families Sciaenidae (croakers), Cichlidae (cichlids), Characidae (characins and tetras), and Serrasalmidae (pacus, piranhas and silver dollars). The dolphin's dentition allows it to access shells of river turtles (such as Podocnemis sextuberculata) and freshwater crabs (such as Poppiana argentiniana). The diet is more diverse during the wet season, when fish are spread in flooded areas outside riverbeds, thus becoming more difficult to catch. The diet becomes more selective during the dry season when prey density is greater. Usually, these dolphins are active and feeding throughout the day and night. However, they are predominantly crepuscular. They consume about 5.5% of their body weight per day. They sometimes take advantage of the disturbances made by boats to catch disoriented prey. Sometimes, they associate with the distantly related tucuxi (Sotalia fluviatilis), and giant otters (Pteronura brasiliensis) to hunt in a coordinated manner, by gathering and attacking fish stocks at the same time. Apparently, there is little competition for food between these species, as each prefers different prey. It has also been observed that captive dolphins share food.

In the wild, the life expectancy of the Amazon river dolphin is unknown, but in captivity, the longevity of healthy individuals has been recorded at between 10 and 30 years. According to a 1986 study of the average longevity of this species in captivity, the lifespan of this species in the United States was only 33 months. Until his death in December 2020, an individual named "Baby" lived up to (at least) 46 years at the Duisburg Zoo in Germany. At the time of his death, he had lived at Duisburg Zoo for 45 years and 9 months.

Breeding is seasonal, and births occur between May and June. The period of birthing coincides with the flood season, and this may provide an advantage because the females and their offspring remain in flooded areas longer than males. As the water level begins to decrease, the density of food sources in flooded areas increases due to loss of space, providing enough energy for infants to meet the high demands required for growth. Gestation is estimated to be around eleven months and captive births take 4 to 5 hours. At birth, calves are 80 centimetres (31 in) long and in captivity have registered a growth of 0.21 metres (0.69 ft) per year. Lactation takes about a year. The interval between births is estimated between 15 and 36 months, and the young dolphins are thought to become independent within two to three years. The relatively long duration of breastfeeding and parenting suggests a high level of parental care. Most couples observed in their natural environment consist of a female and her calf. This suggests that long periods of parental care contribute to learning and development of the young.

The species Inia geoffrensis was described by Henri Marie Ducrotay de Blainville in 1817. Originally, the Amazon river dolphin belonged to the superfamily Platanistoidea, which constituted all river dolphins, making them a paraphyletic group. Today, however, the Amazon river dolphin has been reclassified into the superfamily Inioidea. There is no consensus on when and how their ancestral species penetrated the Amazon basin; they may have done so during the Miocene from the Pacific Ocean, before the formation of the Andes, or from the Atlantic Ocean. There is ongoing debate about the classification of species and subspecies. The IUCN and Committee on Taxonomy of the Society for Marine Mammalogy recognize two subspecies: I. g. geoffrensis (Amazon river dolphin) and I. g. boliviensis (Bolivian river dolphin). A third proposed subspecies, I. g. humboldtiana (Orinoco river dolphin), was first described in 1977. Molecular analysis suggests that the Orinoco dolphins are derived from the Amazon population and are not genetically distinct. Comparative morphological research also indicates that I. g. humboldtiana is not distinguishable from I. g. geoffrensis. However, Cañizales (2020) found that I. g. humboldtiana skulls were morphologically distinct and recommended that it be elevated to species status. In 2012, it was proposed that I. g. boliviensis was a different species based on skull morphology. In 2002, following the analysis of mitochondrial DNA specimens from the Orinoco basin, the Putumayo River (tributary of the Amazon) and the Tijamuchy and Ipurupuru rivers, geneticists proposed that genus Inia be divided into at least two evolutionary lineages: one restricted to the river basins of Bolivia and the other widely distributed in the Orinoco and Amazon. A recent study, with more comprehensive sampling of the Madeira system, including above and below the Teotonio Rapids (which were thought to obstruct gene flow), found that the Inia above the rapids did not possess unique mtDNA. As such the species level distinction once held is not supported by current results. Therefore, the Bolivian river dolphin is currently recognized as a subspecies. In addition, a 2014 study identifies a third species in the Araguaia-Tocantins basin, but this designation is not recognized by any international organization and the Committee on Taxonomy of the Society for Marine Mammalogy suggests this analysis is not persuasive. The Amazon river dolphin is the largest river dolphin. Adult males reach a maximum length and weight of 2.55 metres (8.4 ft) (average 2.32 metres (7.6 ft)) and 185 kilograms (408 lb) (average 154 kilograms (340 lb)), while females reach a length and weight of 2.15 metres (7.1 ft) (mean 2 metres (6.6 ft)) and 150 kilograms (330 lb) (average 100 kilograms (220 lb)). It has very evident sexual dimorphism, with males measuring and weighing between 16% and 55% more than females, making it unique among river dolphins, where females are generally larger than males. The texture of the body is robust and strong but flexible. Unlike in oceanic dolphins, the cervical vertebrae are not fused, allowing the head to turn 90 degrees. The flukes are broad and triangular, and the dorsal fin, which is keel-shaped, is short in height but very long, extending from the middle of the body to the caudal region. The pectoral fins are large and paddle-shaped. The length of its fins allows the animal to perform a circular movement, allowing for exceptional maneuverability to swim through the flooded forest but decreasing its speed. The body color varies with age. Newborns and the young have a dark grey tint, which in adolescence transforms into light grey, and in adults turns pink as a result of repeated abrasion of the skin surface. Males tend to be pinker than females due to more frequent trauma from intra-species aggression. The color of adults varies between solid and mottled pink and in some adults the dorsal surface is darker. It is believed that the d…

The region of the Amazon in Brazil has an extension of 5,000,000 km2 (1,900,000 mi2) containing diverse fundamental ecosystems. One of these ecosystems is a floodplain, or a várzea forest, and is home to a large number of fish species which are an essential resource for human consumption. The várzea is also a major source of income through excessive local commercialized fishing. Várzea consists of muddy river waters containing a vast number and diversity of nutrient rich species. The abundance of distinct fish species lures the Amazon River dolphin into the várzea areas of high water occurrences during the seasonal flooding. In addition to attracting predators such as the Amazon river dolphin, these high-water occurrences are an ideal location to draw in the local fisheries. Human fishing activities directly compete with the dolphins for the same fish species, the tambaqui (Colossoma macropomum) and the pirapitinga (Piaractus brachypomus), resulting in deliberate or unintentional catches of the Amazon river dolphin. The local fishermen overfish and when the Amazon River dolphins are removed from the commercial catch in the nets and lines, it causes damages to the equipment and the capture, as well as generating ill will from the local fishermen. The negative reactions of the local fishermen are also attributed to the Brazilian Institute of Environment and Renewable Natural Resources prohibition on killing the Amazon river dolphin, yet not compensating the fishermen for the damage done to their equipment and catch. During the process of catching the commercialized fish, the Amazon river dolphins get caught in the nets and exhaust themselves until they die, or the local fishermen deliberately kill the entangled dolphins. The carcasses are discarded, consumed, or used as bait to attract a scavenger catfish, the piracatinga (Calophysus macropterus). The use of the Amazon river dolphin carcass as bait for the piracatinga dates back to 2000. Increasing demand for the piracatinga has created a market for distribution of the Amazon river dolphin carcasses to be used as bait throughout these regions. Of the 15 dolphin carcasses found in the Japurá River in 2010–2011 surveys, 73% of the dolphins were killed for bait, disposed of, or abandoned in entangled gillnets. The data do not fully represent the actual overall number of deaths of the Amazon river dolphins, whether accidental or intentional, because a variety of factors make it extremely complicated to record and medically examine all the carcasses. Scavenger species feed upon the carcasses, and the complexity of the river currents make it nearly impossible to locate all of the dead animals. More importantly, the local fishermen do not report these deaths out of fear that a legal course of action will be taken against them, as the Amazon river dolphin and other cetaceans are protected under a Brazilian federal law prohibiting any takes, harassments, and kills of the species. The Amazon river suffers from pollution by mercury from industrial and mining sources. High mercury concentrations were found in muscle tissue from a male Amazon river dolphin in the Tapajos River (Brazil), and in the body and milk of female dolphins. In September 2023, 154 Amazon river dolphins died in Brazil's Lake Tefé following record-high water temperatures of 40 °C (104 °F) and reduced water levels during a drought. While there are ongoing studies by the Mamirauá Institute for Sustainable Development to determine the cause of the deaths, the leading hypothesis is that the elevated temperature caused algae in the lake to release a toxin that attacks the central nervous system.

In 2008, the International Whaling Commission (IWC) expressed concern for captured botos for use as bait in the Central Amazon, which is an emerging problem that has spread on a large scale. The species is listed in Appendix II of the Convention on International Trade in Endangered Species Fauna and Flora (CITES), and Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals, because it has an unfavorable conservation status or would benefit significantly from international co-operation organized by tailored agreements. According to a previous assessment by the Scientific Committee of the International Whaling Commission in 2000, the population of botos appears great and there is little or no evidence of population decline in numbers and range. However, increased human intervention on their habitat is expected to, in the future, be the most likely cause of the decline of its range and population. A series of recommendations were issued to ensure proper follow-up to the species, among which is the implementation and publication of studies on the structure of populations, making a record of the distribution of the species, information about potential threats as the magnitude of fishing operations and location of pipelines. In September 2012, Bolivian President Evo Morales enacted a law to protect the dolphin and declared it a national treasure. In 2018, the species was listed on the Red list of endangered species. Increasing pollution and gradual destruction of the Amazon rainforest add to the vulnerability of the species. The biggest threats are deforestation and other human activities that contribute to disrupt and alter their environment. Another source of concern is the difficulty in keeping these animals alive in captivity, due to intra-species aggression and low longevity. Captive breeding is not considered a conservation option for this species. The Global Declaration for River Dolphins seeks to reverse the decline of river dolphin populations throughout the world. As of early 2024, 11 of the 14 countries that have river dolphins have signed the declaration.

The species Inia geoffrensis was described by Henri Marie Ducrotay de Blainville in 1817. Originally, the Amazon river dolphin belonged to the superfamily Platanistoidea, which constituted all river dolphins, making them a paraphyletic group. Today, however, the Amazon river dolphin has been reclassified into the superfamily Inioidea. There is no consensus on when and how their ancestral species penetrated the Amazon basin; they may have done so during the Miocene from the Pacific Ocean, before the formation of the Andes, or from the Atlantic Ocean. There is ongoing debate about the classification of species and subspecies. The IUCN and Committee on Taxonomy of the Society for Marine Mammalogy recognize two subspecies: I. g. geoffrensis (Amazon river dolphin) and I. g. boliviensis (Bolivian river dolphin). A third proposed subspecies, I. g. humboldtiana (Orinoco river dolphin), was first described in 1977. Molecular analysis suggests that the Orinoco dolphins are derived from the Amazon population and are not genetically distinct. Comparative morphological research also indicates that I. g. humboldtiana is not distinguishable from I. g. geoffrensis. However, Cañizales (2020) found that I. g. humboldtiana skulls were morphologically distinct and recommended that it be elevated to species status. In 2012, it was proposed that I. g. boliviensis was a different species based on skull morphology. In 2002, following the analysis of mitochondrial DNA specimens from the Orinoco basin, the Putumayo River (tributary of the Amazon) and the Tijamuchy and Ipurupuru rivers, geneticists proposed that genus Inia be divided into at least two evolutionary lineages: one restricted to the river basins of Bolivia and the other widely distributed in the Orinoco and Amazon. A recent study, with more comprehensive sampling of the Madeira system, including above and below the Teotonio Rapids (which were thought to obstruct gene flow), found that the Inia above the rapids did not possess unique mtDNA. As such the species level distinction once held is not supported by current results. Therefore, the Bolivian river dolphin is currently recognized as a subspecies. In addition, a 2014 study identifies a third species in the Araguaia-Tocantins basin, but this designation is not recognized by any international organization and the Committee on Taxonomy of the Society for Marine Mammalogy suggests this analysis is not persuasive.