Amazon Basin of Brazil, Colombia, Ecuador, Guyana, and Peru.
Biogeographic Regions: neotropical (Native )
South America (Amazon R. basin)
The Amazon ox manatee is gray and bears a white patch on its chest or several white markings on its chest and abdomen. Its body is covered with fine hairs and its upper and lower lips are covered with thick bristles. It has two axillary mammae. The largest manatee recorded was a male 2.8m in length.
Other Physical Features: endothermic ; bilateral symmetry
Average mass: 480000 g.
Average basal metabolic rate: 55.015 W.
Habitat and Ecology
Individuals engage in long seasonal movements, moving from flooded areas during the wet season to deep water-bodies during the dry season (Kendall 2001, M. Marmontel et al. unpubl.). While the whitewaters provide them with plentiful food, deep lakes function as refuges during the low-water season, where animals are less vulnerable to hunting.
Only one calf is produced at a time. Although no specific studies are available for the species in the wild, it is believed that the reproductive cycle is similar to the West Indian Manatees, with a long gestation and lactation period (up to 24 months), and a birthing interval of 2 to 3 months; age at sexual maturity is unknown.
Amaxonian manatees inhabit the dense vegetation in blackwater lakes, oxbows, and lagoons.
Habitat Regions: tropical ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; coastal
Trichechus inunguis feeds upon aquatic vegetation such as grasses, water lettuce (Pisitia), and water hyacinths. It is also known to eat floating palm fruits. Captives are capable of eating 9 to 15 kilograms of leafy vegetables per day.
Life History and Behavior
Perception Channels: tactile ; chemical
Status: captivity: 12.5 years.
Status: wild: 30.0 years.
Lifespan, longevity, and ageing
These manatees breed throughout the year and gestate for approximately one year. Usually one young is born. An individual thought to be a newborn measured 739mm in length. The mothern and calf have a long-lasting bond. The mother may carry the young on her back or clasped to her side. The lifespan of this animal is unknown, but individuals have lived past twelve and a half years in captivity.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
Average birth mass: 12500 g.
Average gestation period: 328 days.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 1096 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 1096 days.
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2007Vulnerable (VU)
- 1996Vulnerable (VU)
- 1994Vulnerable (V)
- 1990Vulnerable (V)
- 1988Vulnerable (V)
- 1986Vulnerable (V)
- 1982Vulnerable (V)
- 1965Status inadequately known-survey required or data sought
Trichechus inunguis is listed as Cites-Appendix I, as U.S. E.S.A.-Endangered, and as IUCN-Vulnerable. They have been hunted by Amazonian Indians with nets and harpoons for centuries. In the 1930s and 1940s they were killed by the thousands for their hides, which were used to make water hoses and machine belts.
IUCN Red List of Threatened Species: vulnerable
Date Listed: 06/02/1970
Lead Region: Foreign (Region 10)
Where Listed: Entire
Population location: Entire
Listing status: E
For most current information and documents related to the conservation status and management of Trichechus inunguis , see its USFWS Species Profile
Whatever the current population size, the population trend is most likely decreasing, given the species slow reproduction (sirenian populations grow at an annual rate of approximately 5%; Marsh et al. 1984c, Packard 1985) and levels of exploitation (Marmontel et al. 1992). During extensive interviews conducted with local inhabitants throughout the range of the species, conflicting responses were obtained. In Brazil, Lazzarini and Picano (pers. comm. 2005) were of the opinion that, due to the work by the Manaus Energia Environmental Program and other conservation actions, hunting is decreasing in the lower Uatum river (from 23 in 1994 - and a high of 73 in 1995 - to zero in 2003 and 2004 and one in 2005). The progressive increase in the number of young calves arriving at rehabilitation centers in Brazil in the past five years, has also led several researchers to suspect that the species may be undergoing some recovery, or that the increase is simply a reflection of the awareness campaigns implemented, with a concomitant increase in the number of rescued calves (Rosas and da Silva pers. comm. 2005). Alternatively, it may also suggest that calf takes are on the rise (and see Threats).
On the other hand, manatee numbers are thought to have been decreasing in the past few years in all known areas of occurrence in Colombia. If indeed there are less than 100 manatees in the area (Kendall 2001), then the 7 to 11 animals killed/year over the period 1988-2001 would certainly lead to a reduction in the population. However, since Fundacin Omacha started its work in the area of Puerto Nario, the population in this area at least may have stabilized due to the reduction in hunting (only two individuals in the past two years) (Kendall pers. comm. 2005).
In the early 1980s, manatees were reported to be abundant in most of the lagoons and black water rivers of Ecuadors Cuyabeno Reserve, but this population was being persecuted for meat by Peruvian and Ecuadorian militaries. Timm et al. (1986) suggested that there were 250 adult individuals in Ecuador, and that no subpopulation exceeded 50 individuals; they estimated that if the then level of harvest went on unabated, Amazonian manatees would disappear from Ecuador within 10 to 15 years. Timm et al. (1989) stated that the Siona Indians then practiced a self-imposed ban on manatee hunting because of low manatee populations. However, some of the Siona never knew about this ban, and it seems possible that hunting continued (C. Castro pers. comm. 2005). Amazonian manatees still exist in the Cuyabeno River, but likely in low numbers. In the Lagartococha system, Peruvian hunters claim to have hunted manatees until about 10 years ago; since that time, they have not seen any manatees in the area. Although the information from recent interviews is contradictory, the general consensus is that the population is decreasing.
In Peru, in an area in the Samiria river, average sightings over the 2003 to 2005 period were sufficient to suggest that were was no apparent decrease in the population, and that the population is stable, albeit at low numbers (R. Bodmer pers. comm. 2005). However, Ulloa Gomez (2004) believes that reports from hunters, a decrease in the number of manatee sightings, the absence of manatees in sites previously occupied, and results from field surveys in Pacaya Samiria, lend evidence to the hypothesis that manatee populations are declining.
Illegal hunting, for both subsistence and local use, is considered the main threat to manatees in the Amazon. Manatee populations have supported a tremendous take in past centuries and, although not at commercial levels, hunting still takes place throughout the region. Manatee meat is highly valued, but all the other products are used as well (fat and skin are used in cooking and as medicine, bones are turned into utilitarian pieces and charms, and the skin produces very resistant leather).
Hunters usually sell products to neighbours and nearby communities, but the meat is sometimes sold in markets of local towns. There is also some traffic between cities to sell manatee products in local markets (Evangelista 2005 pers. comm.). Meat is sold in natura, or as mixira or subproducts such as sausage. The mixira, which is the meat preserved in its own fat, is one of the products that prolongs the pressure on the species, since it commands a high price. Meat is sold in local produce fairs or markets in the interior, or by order directly with the hunter. Public markets in Brazil (Manaus, Manacapuru, Novo Airo, Tef, Silves, Itapiranga and Itacoatiara, Santarem, Belem, Monte Alegre and Almeirim), Colombia (Puerto Narino, Leticia, Atacuari) and Ecuador also illegally offer the meat for sale, with prices ranging from U$0.23 to U$1.87 (Lazzarini and Picano pers. comm. 2005, Hage pers. comm. 2005). A 60-l can of mixira sells for approximately U$168 (Lazzarini and Picano pers. comm. 2005). Since a large manatee could yield as much as 200 kg of meat, which could be dried or salted, this could provide some two months wages (Kendall 2001).
The use of traditional harpoons remains the most widespread technique for hunting manatees - corresponding to 70% to over 90% of all takes (Kendall et al. 2005, Sartor et al. in prep, M. Marmontel unpubl.). So far, fishing traps with harpoons attached have only been recorded for Peru (Reeves et al. 1996, Ulloa Gomez 2004) and on the Colombian-Peruvian border (Orozco 2001). Although illegal in both countries, between 1998 and 2003 at least 14 manatees were killed on the Peruvian side of the border; this technique accounted for 30% of intentional mortality from 1998 to 2003 in Colombia (Kendall et al. 2005). Kendall (2001) and Orozco (2001) believed this practice to be localized and becoming increasingly uncommon, although Peruvian hunters think this technique might be responsible for an increase in manatee hunting (Ulloa Gomez 2004). Fishermen will close areas where manatees are known to gather to mate, in order to harpoon them (M. Leitao pers. comm., 2005), or hit the water with sticks to disorient manatees with the noise (batio) and then harpoon them in channels and lakes closed with gillnets (Lima et al. 2001).
The use of nets has been on the increase over the past few years. Kendall et al. (2005) calculated that 15% of hunting mortality in Colombia over the period 1998 to 2003 was due to netting. Netting has sometimes had large-scale impacts: in 1999, a large trawl net deployed by a freezer boat caused the death of 14 animals (Lazzarini and Picano pers. comm. 2005) in the Purus river, while in 1998 a single net setting is said to have trapped 60 animals in Manacapuru (AM) (Lazzarini and Picanco pers. comm. 2005). Of particular concern is the development of special gillnets designed to catch manatees. In 1992, three cases of non-calf entangled manatees were documented in the Brazilian Amazon, while between 1999 and 2000, four adult manatees were caught in nets (Lazzarini and Picano pers. comm. 2005). Although unclear if accidental or intentional, the large size of the adults suggests the use of strong nets built specifically for the specific purpose of catching manatees.
Take estimates are available only for a few sites where conservation and research projects are taking place. The Amazonas branch of the Brazilian environmental agency has been attempting to survey and control all manatee hunting efforts since 1995, but results are variable, primarily due to funding inconsistencies. The most complete set of data are from the lower Uatuma river (surveyed by Centro de Preservacao e Pesquisas de Mamiferos Aquaticos) and mid-Solimoes areas in Brazil (Mamiraua and Amana Sustainable Development Reserves, managed by Mamiraua Institute of Sustainable Development), and the Puerto Narino area in Colombia (under Fundacion Omachas research) for very limited areas (Table 1, in Supplementary Material).
See the Supplementary Material for Table 1: catch estimates for T. inunguis in Brazil and Colombia.
Very limited information is available for Ecuador (in 1996 four manatees are said to have been killed by the Siona Indians; and in 1998 eight manatees - six by the Siona and two by the Quichua; C. Castro pers. comm. 2005). Likewise, no long-term data are available for Peru either; however, during May and June 2004 alone, seven manatees were taken in only two villages from the Samiria River basin, suggesting high hunting pressure (Ulloa Gomez 2004). Between 1998 and 2003, 47 manatees were recorded hunted in the area of Puerto Nario (Zaragoza to Atacuari) (Kendall et al. 2005). In the Puerto Nario area, hunting has been on the decline in the past five years: with the inception of educational campaigns, numbers of culled manatees decreased from ten in 1998/1999 to four in 2003 and two in 2004 (Kendall pers. comm. 2005).
Extreme droughts may help make the manatee an easier prey item for hunters, by causing isolation and entrapment (Reeves et al. 1996, Ulloa Gomes 2004, Sartor et al. in prep., M. Marmontel pers. obs.). In 1994, an estimated 10 animals were taken from a poo (a deep-water site where animals concentrate during dry seasons) in Sao Sebastiao do Uatuma (Lazzarini and Picanco pers. comm. 2005); in 1995, 60 were hunted between July and September only, in a breathing hole across from the Urucara (AM) town, and one fisherman alone caught 11 manatees (Lazzarini and Picano 2005). During the drought of 1998, multiple numbers of manatees were taken in one day in three different poos of the Coari town (AM) area (16 in the Poo da Freguesia; Tressoldi and Lazzarini 2000; 16 in Pixuma and 8 in Tucuma; Lazzarini and Picanco pers. comm. 2005; and 18 in Prego Community (Purus) (Lazzarini and Picanco pers. comm. 2005). In the 2005 drought, at least five were killed in the Tefe Lake across from the Tefe town (AM) and approximately 120 were taken in the Coari area, according to information gathered by the environmental agency and reported in local newspapers.
Incidental mortality, orphaned calves, and illegal captivity
With an increasing use of gillnets to hunt manatees, there has been a concomitant rise in incidental calf mortality in the past few years, and this is now a major threat to Amazonian manatees in all range countries (Rosas and da Silva pers. comm. 2005, R. Bodmer pers. comm. 2005, Utreras and Zapata 2005, Ulloa Gomez 2004). Although young animals usually end up drowning in the nets, if they do survive then they are usually kept alive for later sale, since young animals have little meat for immediate consumption (Kendall 2001, Orozco 2001).
The number of rescued calves every year has been increasing, but this number is certainly only a small sample of occurrences in the Amazon (Rosas and da Silva pers. comm. 2005). In the past five years, at least six calves became entangled in nets across channels in Colombia (S. Kendall pers. comm. 2005). Calves captured in Colombia are taken to Leticia and sometimes to Caballo Cocha, Peru (Orozco 2001). There are also reports of manatee calf commerce in the border between Brazil and Colombia (Lazzarini and Picano pers. comm. 2005), and there were at least three cases reported of calves captured in Peru and offered for sale in Colombia between 2003 and 2005 (Kendall pers. comm. 2005).
Between 1992 and 2005, CPPMA (Centro de Preservao e Pesquisa de Mamferos Aquticos) received an average of four calves/year, with numbers increasing when a heavy drought was in place. Of the 41 calves rescued, 23 (56%) were caught in gillnets, but only four accidentally, while the others were caught in nets set up to catch them with the intent to sell, and even to catch on request (in five cases the mother was also caught and killed). In 13 (32%) of the orphan cases, the calves were harpooned (CPPMA, Picano and Lazzarini, 2005, unpubl.).
Calves (wounded or not) are sometimes sold as pets (Rosas and da Silva pers. comm. 2005), kept in pools or areas close to water bodies, and sold or given to politicians, authorities, and influential persons. A boat owner on the route Belm-Santarm allegedly keeps 10 in a lake near Manaus and has paid up to US$150 for one (Sartor pers. comm. 2005). Siona and Quechua indians keep manatees as pets, but raise them for food (C. Castro pers. comm. 2005).
Habitat alteration and disturbance
Anthropogenic actions have resulted in pollution, loss, alteration and fragmentation of habitats used by the Amazonian manatee (Rosas and da Silva pers. comm. 2005, Min. Amb. and F. Omacha 2004).
Deforestation and contamination by mercury, oil or pesticides, are potential hazards to the manatees food supply (Rosas et al. 1991), and the construction of hydroelectric dams may isolate populations, limiting genetic variability (Rosas 1994). Brazil has planned 400 dams, 46 of them at the phase of projects, two of which are mega-enterprises in the Amazon regions (Madeira and Xingu rivers). Both gold mining and deforestation contribute to the pollution of the water system (Amorim et al. 2000, Dolbec et al. 2000). Roots of floating and rooted aquatic plants (Paspalum, Eicchornia, Salvinia) have been shown to be important methylation sites (Guimaraes et al. 2000a,b).
An important potential problem in Ecuador are oil spills (Utreras and Zapata pers. comm. 2005), the last one having occurred in Cuyabeno Lagoon 10 years ago (C. Castro pers. comm. 2005). In 2004, Petrobras (a Brazilian multinational company) was granted permission to explore oil in Yasuni National Park, which will involve considerable traffic in the Tiputini river, mainly during the building stages, but also large boat traffic during the 20-year operation (J. Proao pers. comm. 2005). Local indigenous leaders denounce that toxic residues, such as benzene, xylene and alcatrao, are being discharged into the river as a result of prospecting activities (http://www.amazonia.org.br 23 jan06). In some cases indigenous peoples no longer bathe in the river due to oil contamination (http://www.radiobras.gov.br).
Amazonian human populations are generally at low densities except in the large capital cities, but all of the issues above could be magnified by the increase in human population. In some parts of Colombia and Peru, manatee absence from areas where they were previously recorded may be partially attributed to increased boat use and town growth (Kendall 2001, Orozco 2001, Kendall et al. 2004, Ulloa Gomez 2004). The current process of placing asphalt on the BR-163 road connecting Cuiaba in Mato Grosso to Santarem in PA, is expected to bring the typical colonization fronts and economic occupation which have previously created disorderly migration, deforestation and predatory exploration of natural resources, which shall add to present threats to manatee. The main economic activity associated with that road, soy plantation, will likely cause increased levels of deforestation, siltation and pesticide runoff. Boat traffic tends to increase even in smaller towns, but the heavy traffic of barges associated with the setting up of a hydrovia for soybean transportation could impact both manatees directly and their food supply.
Presently, INPA (Instituto Nacional de Pesquisas da Amaznia) cares for 34 captive manatees including eight calves, 18 juveniles and eight adults (da Silva et al. 2006). CPPMA currently maintains 31 manatees, mostly orphans. So far, the Centro Mamiferos Marinhos-Conselho Nacional de Seringueiros facility in Alter-do-Cho (PA, Brazil) has rescued six orphans (two of which died) and a sick adult manatee (Luna 2005 pers. comm.).
Relevance to Humans and Ecosystems
Manatees are a source of food for many native peoples.
The Amazonian manatee (Trichechus inunguis) is a species of manatee of the order Sirenia. It is found living in the freshwater habitats of the Amazon Basin in Brazil, Peru, Bolivia, Colombia and Ecuador. It has thin, wrinkled skin, and is almost hairless, but has "whiskers" around its mouth. It also has a distinct white breast patch, with fine hairs scattered over its body. It is also known as the Amazon Manatee sea cow.
The Amazonian manatee is the second-smallest species of manatee after the dwarf manatee (Trichechus pygmaeus) from Brazil. However, the validity of the dwarf manatee as a species is the subject of debate, with some believing it to be an immature Amazonian manatee.
The specific name, inunguis is latin for "nailless." The genus name Trichechus, comes from latin meaning "hair", referencing the whiskers around the manatee's mouth.
Ranges of body weight and size observed are 7.5–346.5 kg and 76.0 –255.5 cm for captive males, 8.1–379.5 kg and 71.0–266.5 cm for captive females, and 120.0–270.0 kg and 162.0 –230.0 cm for free-ranging manatees, respectively. The maximum actual Amazonian manatee weight reported is 379.5 kg. Calves of the species are born weighing 10–15 kg and 85 –105 cm long.
Amazonian manatees are large, cylindrically shaped mammals, with forelimbs modified into flippers, no free hind-limbs, and the rear of the body in the form of a flat, rounded, horizontal paddle. The flexible flippers are used for aiding motion over the bottom, scratching, touching and even embracing other manatees, and moving food into and cleaning the mouth. The manatee's upper lip is modified into a large bristly surface, which is deeply divided. It can move each side of the lips independently while feeding. The general coloration is gray, and most Amazonian manatees have a distinct white or bright pink patch on the breast.
The manatee does not have incisors or canine teeth, only cheek teeth (molars). Molars designed to crush vegetation form continuously at the back of the jaw and move forward as older ones wear down. The older ones eventually fall out, while new ones come in at the rear of the jaw to replace them.
The Amazonian manatee lacks nails on its flippers, setting it apart from other manatees. An almost unique feature (amongst mammals) of the manatee is the constant replacement of molar teeth; new teeth enter at the back of the jaw and replace old and worn teeth at the front. The order's closest relatives, the elephants, also have teeth that get replaced, but have only a limited set of these replacement teeth.
Behavior and biology
The Amazonian manatee is the only sirenian that lives exclusively in freshwater habitat. The species relies on changes in the peripheral circulation for its primary mechanism for thermoregulation by using sphincters to deflect blood flow from areas of the body in close contact with ocean. They also rely on subcutaneous fat to reduce heat loss.
Manatees have nostrils, not blowholes like other aquatic mammals, which close when under water to keep water out and open when above water to breath. Although manatees can remain under water for extended periods, surfacing for air about every five minutes is common. The longest documented submergence of an Amazonian manatee in captivity is 14 minutes.
Manatees make seasonal movements synchronized with the flood regime of the Amazon Basin. They are found in flooded forests and meadows during the flood season, when food is abundant. The Amazonian manatee has the smallest degree of rostral deflection (25° to 41°) among sirenians, an adaptation to feed closer to the water surface. It is both nocturnal and diurnal and lives its life almost entirely underwater. Only its nostrils protrude from the surface of the water while it searches river and lake bottoms for vegetation.
The Amazonian and Florida manatees are the only manatees known to vocalize. They have been observed vocalizing alone and with others, particularly between cows and their calves.
The manatees themselves feed on a variety of aquatic macrophytes, including aroids, grasses, bladderwarts, hornworts, water lilies, and particularly, water hyacinths. Maintaining an herbivorous diet, the manatee has a similar post-gastric digestive process to that of the horse. The manatee consumes approximately 8% of its body weight in food per day.
During the July–August dry season when water levels begin to fall, some populations become restricted to the deep parts of large lakes, where they often remain until the end of the dry season in March. They are thought to fast during this period, their large fat reserves and low metabolic rates – only 36% of the usual placental mammal metabolic rate – allowing them to survive for up to seven months with little or no food.
Reproduction and lifecycle
The Amazonian manatee is a seasonal breeder with a gestational period of 12–14 months and a prolonged calving period. Most births take place between December and July, with about 63% between February and May, during a time of rising river levels in their native region. After the calf is born, it will begin to eat while staying with its mother for 12 – 18 months.
Population and distribution
As of 1977 the population count of the Amazonian Manatee was estimated to be around 10,000. As of now the total population count is undetermined, however the population trend seems to be decreasing. They are mainly distributed throughout the Amazon River Basin in northern South America, ranging from the Marajó Islands in Brazil through Colombia, Peru, and Ecuador. They are occasionally found overlapping with the West Indian Manatee along the coasts of Brazil.
Amazonian manatees occur through most the Amazon River drainage, from the headwaters, in Colombia, Ecuador and Peru to the mouth of the Amazon (close to the Marajó Island) in Brazil over an estimated seven million square kilometers. However, their distribution is patchy, concentrating in areas of nutrient-rich flooded forest, which covers around 300,000 km²  They also inhabit environments in lowland tropical areas below 300 m asl, where there is large production of aquatic and semi-aquatic plants; they also calm, shallow waters, away from human settlements
The Amazonian manatee is completely aquatic and never leaves the water. It is the only manatee to occur exclusively in freshwater environments. The Amazonian manatee favors backwater lakes, oxbows, and lagoons with deep connections to large rivers and abundant aquatic vegetation They are mainly solitary but sometimes they will gather in small groups consisting of up to eight individuals. They engage in long seasonal movements, moving from flooded areas during the wet season to deep water-bodies during the dry season
Natural predators include jaguars, sharks, and crocodiles.
The IUCN red list ranks the Amazonian manatee as vulnerable. Population declines are primarily a result of hunting, as well as calf mortality, climate change, and habitat loss. However, due to their murky water habitat it is difficult to gain accurate population estimates.
There are no national management plans for the Amazonian Manatee, except in Colombia. Currently,[when?] the INPA takes care of 34 captive manatees and the CPPMA is caring for 31 manatees. The manatee has been protected by Peruvian law since 1973, via Supreme Decree 934-73-AG, prohibiting hunting and commercial use of the manatee.
Hunting remains the largest problem and continues in much of its range, even within reserves. In 1986, it was estimated that the hunting levels in Ecuador were unsustainable and it would be gone from this country within 10–15 years. While hunting still occurs, an increasing risk to its continued survival in Ecuador is now believed to be the risk of oil spills. The oil exploration also means an increase in boat traffic on the rivers.
The Amazonian manatees of Peru have experienced much of their decline due to hunting by human populations for meat, blubber, skin and other materials that can be collected from the manatee. Such hunting is carried out with harpoons, gillnets, and set traps. Much of this hunting occurs in the lakes and streams near the Pacaya-Samiria National Reserve in northeastern Peru. The species is slow-moving, docile, and is often found feeding at the surface of the lakes and rivers it inhabits. Manatees are also at risk from pollution, accidental drowning in commercial fishing nets, and the degradation of vegetation by soil erosion resulting from deforestation. Additionally, the indiscriminate release of mercury in mining activities threatens the entire aquatic ecosystem of the Amazon Basin.
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