Animal Info - Boto (Amazon River Dolphin)
(Other Names: Amazon Dolphin, Amazonas-Delphin, Boto Vermelho, Bouto, Bufeo, Bufeo Colorado, Bufeo de Río, Dauphin de l'Amazone, Delfín Amazónico, Inia, Pink Dolphin, Pink Freshwater Dolphin, Pink Porpoise, Tonina)
Inia geoffrensis
Status: Vulnerable
4. Data on Biology and Ecology (Size and Weight, Habitat, Age to Maturity, Gestation Period, Birth Season, Birth Rate, Early Development, Maximum Age, Diet, Behavior, Social Organization, Density and Range)
Pictures: Boto #1 (10 Kb JPEG) (Intl. Soc. Pres. Trop. Rainfor.) ; Boto #2 (11 Kb JPEG); Boto #3 (29 Kb JPEG) (Swiss Cet. Soc.)
The boto is the largest river dolphin, weighing up to 180 kg (400 lb) with a length up to 2.6 m (8.5'). Most adult botos are pink, although some have a darker back or are partially gray. Although the boto's eyes appear small and inconspicuous, they are actually, in the skull, as large as those of marine dolphins. Thus the boto can see well. On the other hand, it can also rely on its sonar as it swims through a murky flooded forest. 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.
The boto 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, particularly the deeper waters in these areas. 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. Botos 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 boto is a generalist feeder. Its diet is known to include over 50 species of smaller fish, as well as freshwater crabs and river turtles. Feeding is usually done close to shore, in shallow bays, in flooded forests, or at confluences. The boto is a slow-moving animal that usually swims at 2.4 - 5.1 km/h (1.5 - 3.2 mi/h) with bursts of more than 23 km/h (14 mi/h). Its dives usually last less than 1 - 2 minutes. The boto is mainly solitary, with less than 1/4 of sightings involving pairs (usually a mother and calf). Larger groups are rarely seen, although loose aggregations have been observed at feeding areas.
The boto 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. The boto 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.
*** The boto has benefited 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 this dolphin. (Best & da Silva 1993)
*** The boto readily associates with man and is playful, sometimes retrieving thrown objects and even soliciting physical contact. When swimming, dolphins may nip divers, play tag or take the diver's hand under its flipper and tow him or embrace him. Wild botos grasp fishermen's paddles, rub against canoes, and may become quite tame. (Best & da Silva 1993)
*** 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. (Schmidt-Lynch 1994)
*** Etymology of the boto's scientific name: the genus name ("Inia") - this 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". (Montgomery 2000)
1996 - 2006: Vulnerable (Criteria: A1cd) (IUCN 2006)
Countries Where the Boto Is Currently Found:
2006: Occurs in Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela. (Amazon and Orinoco River basins) (IUCN 2006)
2004: Probably tens of thousands (IUCN 2004)
The boto 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, possibly little different from that in pre-colonial settlement times, is as follows: 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')). (Best & da Silva 1993, da Silva & Martin 2000, Culik 2003b, Reeves et al. 2003)
Distribution Map #1 (3 Kb JPEG) (Cetacea)
Distribution Map #2S (18 Kb JPEG) (WCMC/CMS) (small map)
Distribution Map #2L (51 Kb JPEG) (WCMC/CMS) (larger map)
The boto 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 (da Silva & Martin 2000) . Threats include interactions with fisheries, hydroelectric development, deforestation, and pollution from agriculture, industry and mining.
Although there is no regular hunt for botos, they are sometimes killed and maimed deliberately by fishermen to protect their catch and gear, or in retaliation for perceived competition for fish resources. Most human-caused mortality is incidental. However, in the absence of any systematic effort to record the bycatch, and with so little information on the species' abundance and population biology, it is impossible to determine whether there are significant conservation problems. (Reeves et al. 2003)
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. (IWC 2000, Reeves et al. 2000)
Length: 2 - 2.6 m (6.5 - 8.5'); Weight: females: 80 - 120 kg (180 - 260 lb); males: 120 - 180 kg (260 - 400 lb) (da Silva & Martin 2000) .
The boto uses fresh waters of all types as habitat but is not found in estuaries or other saline waters. It is found at water temperatures from 23 - 30 deg C (73 - 86 deg F). It appears to favor microhabitat areas such as confluences, sharp bends, areas below rapids, smaller channels running parallel to the main river, and sandbars, particularly the deeper waters in these areas. In large white water rivers, most of its activity seems to be directed swimming, as though the animals were transiting between patches of the preferred microhabitat areas. (Klinowska 1991, Leatherwood et al. 2000, Culik 2003b)
In the central Amazon basin, large changes in water levels affect the local distribution of botos. A 10 - 15 m (33 - 49') increase in water level during the flood season leads to the inundation of large areas of forest. (The flood season occurs during December - June. Water levels peak in May and June, and reach their lowest levels between September and early November.) Botos move out of the main river into channels and small lakes, and then into the forest itself, as the rising waters flood the forest. It is then able to use both the flooded forest and grasslands, even swimming among the trees. Shallow water is frequently used for feeding. (IWC 2000, Klinowska 1991, da Silva & Martin 2000)
The boto occurs in the Brazilian Shield Amazonian Rivers & Streams and Varzea & Igapo Freshwater Ecosystems Global 200 Ecoregions. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)
Age of females at first birth is estimated to be between 6 - 10 years (IWC 2000) .
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'). (Klinowska 1991)
The estimated gestation period is 11 months (IWC 2000) .
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 boto'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. (Culik 2003b)
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%. (IWC 2000)
Early Development:
Lactation appears to be prolonged (well over a year) (Klinowska 1991) . Mother and offspring stay together for at least 2.5 years (Montgomery 2000) .
One animal was still alive after 18 years in captivity; longevity is probably about 30 years (Nowak 1999) .
The boto 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 more often a solitary feeder, the boto sometimes forms loose groups that cooperate in herding and attacking schools of fish. (Klinowska 1991, Best & da Silva 1993, Schmidt-Lynch 1994, Montgomery 2000, Burnie & Wilson 2001)
Activity Patterns: The boto'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 dolphins in evidence on cloudy or rainy days. It apparently is non-migratory, in that regular long journeys do not appear to be undertaken. (Klinowska 1991)
One unusual example of dolphins utilizing both the deeper and shallower portions of habitat was reported by Leatherwood et al. 2000. Thirteen boto were observed continuously for 85 minutes in a sharp river bend with a sandbank. The boto appeared to follow a pattern. Calves circled slowly over the shallow water on the sandbank side, alone or in pairs. The larger boto, some of which were presumed to be the calves' mothers, dived and surfaced in deep water near mid-river for up to four minutes, then returned to the shallows, each joining one of the calves. After a brief reunion with the calves, the larger animals would return to the deep water. There was no suggestion that fish were being brought to the calves in the shallows. Rather, this scenario seemed to represent a kind of "nursery," with the microhabitat partitioned to accommodate the needs of both the adults and the young, dependent calves.
Senses: Though its eyes appear small, they are actually, in the skull, as large as those of marine dolphins. Thus the boto can see quite well, except that its bulging cheeks hamper downward views. This is overcome by swimming upside down. On the other hand, in the murky water of some rivers, the boto relies on its sonar. Utilizing its flexible neck, as it swims through the flooded forest, a boto 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. The boto also has sensory bristles on its beak that allows it to feel for food in the river's depths. (Cetacea, Schmidt-Lynch 1994, Montgomery 2000)
Diving: The boto's dives usually last less than 1 - 2 minutes, but they can last up to 4 minutes. In central Brazil, botos surface very briefly, rarely twice in quick succession, and almost never in a predictable position (da Silva & Martin 2000) .
Swimming: The boto is a slow-moving animal that usually swims at 2.4 - 5.1 km/h (1.5 - 3.2 mi/h) with bursts of more than 23 km/h (14 mi/h). It is able to move its head in any direction, due to the unfused vertebrae in its neck. It is exceptionally flexible and maneuverable, able to swim in confined and shallow areas, and among trees in the flooded forest. (Cetacea, da Silva & Martin 2000) .
As is typical for river dolphins, the boto 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.
Density:
- 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 channel (IWC 2000) .
- In a study in the Peruvian Amazon, the densities of boto 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). (Leatherwood et al. 2000)
- Densities of botos reported from several surveys (Culik 2003b) :
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)
Seasonal movements of botos are related to the migration of fish and the annual flooding cycle of the river. Botos have undefended home ranges, and seasonal movements are probably slight shifts in the boundaries of the core area. Animals from the central Amazon region (Negro and Tocantins Rivers) occupy the same range year-round. (Best & da Silva 1993)
Best & da Silva 1993, Burnie & Wilson 2001, Cetacea, Culik 2003b, Eisenberg & Redford 1999, Intl. Soc. Pres. Trop. Rainfor., IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2003a, IUCN 2006, IUCN 2004, IWC 2000, Klinowska 1991, Leatherwood et al. 2000, Montgomery 2000, Nowak 1999, Olson & Dinerstein 1998, Olson & Dinerstein 1999, Reeves et al. 2000, Reeves et al. 2003, Schmidt-Lynch 1994, da Silva & Martin 2000, Swiss Cet. Soc., WCMC/CMS