Overview

Brief Summary

Fossil species

recent & fossil

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Biology

Amazonian manatees are aquatic mammals and live almost entirely underwater. Indeed the three manatee species and the closely related dugong are unique in that they are the only plant-eating marine mammals (7). They feed entirely on aquatic vegetation near lake edges, such as emergent grasses, water lettuce and floating vegetation. Shy and secretive, only their nostrils protrude from the surface of the water to breathe as they search for lush vegetation (7). Despite being slow grazers they are able to consume up to eight percent of their body weight in one day (2) (7). Most feeding occurs during the wet season, when they graze upon new plant growth in seasonally flooded water. During the dry season, individuals return to the main water courses, or to deep flooded backwaters where herds congregate (7). Here they may not eat for weeks or months due to the lack of food. However, manatees have large fat reserves and slow metabolic rates; at one third of the usual rate for a mammal of its size. This enables them to survive until the water levels rise again and food becomes more abundant (2) (7). These mammals are active by day and night. They are found individually or in small groups of between four and eight animals (7). Mothers nurse their calves from a teat behind the flipper, and it is the mothers and calves that form the closest bonds (7) (8). A single calf is born after a gestation period of approximately 13 months. It is dependant on its mother for a considerable time, so interbirth intervals may be as long as three and a half years or more. Individuals mature at five or six years of age and members maintain group contact by underwater vocalisations (8). The lifespan of this animal is unknown, but individuals have lived past twelve and a half years in captivity (7).
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Description

The Amazonian manatee is a most bizarre-looking aquatic mammal, and was first described as a curious combination of a hippopotamus and a seal (6). Its body is large, dark grey to black and smooth-skinned, and its forelimbs are modified into flippers like a seal's (17). It has no hind limbs, and the rear of the body forms a flat, rounded horizontal paddle (7). The head is rounded, with nostrils on the upper surface of the snout (8). The Amazonian manatee is smaller and more slender than the other two manatee species (West Indian manatees Trichechus manatus and West African manatees T. senegalensis) (7). It can also be identified by the lack of nails on its flippers, a characteristic referred to in its scientific name, T. inunguis, which literally means 'no nails' (9). A 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 (10). Recent evidence suggests that manatees may possess a unique 6th sense that enables them to detect pressure changes through sensory hairs (11).
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Distribution

Amazon Basin of Brazil, Colombia, Ecuador, Guyana, and Peru.

Biogeographic Regions: neotropical (Native )

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Range Description

Amazonian manatees occur through most the Amazon River drainage, from the headwaters, in Colombia, Ecuador and Peru (Timm et al. 1986) to the mouth of the Amazon (close to the Marajó Island) in Brazil (Domning 1981) over an estimated seven million square kilometers. However, they are patchily distributed, concentrating in areas of nutrient-rich flooded forest, which covers around 300,000 km² (Junk 1997).
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South America in freshwater (Amazon River drainige, possibly also in Orinoco)
  • UNESCO-IOC Register of Marine Organisms
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Historic Range:
South America (Amazon R. basin)

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Range

This species is found in the Amazon River Basin from the river mouth to the upper reaches of calm water tributaries of Brazil, Colombia, Ecuador, Guyana, and Peru (2) (17).
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Physical Description

Morphology

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.

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Ecology

Habitat

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

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Habitat and Ecology

Habitat and Ecology
Amazonian manatees inhabit environments in lowland tropical areas below 300 m asl, where there is large production of aquatic and semi-aquatic plants; they also favor calm, shallow waters, away from human settlements.

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 Manatee’s, 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.

Systems
  • Freshwater
  • Marine
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Inhabits areas of the Amazon River where there are freshwater lagoons, oxbow lakes and blackwater lakes. It requires waterways with deep connections to large rivers and abundant aquatic vegetation (7).
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Trophic Strategy

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.

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Life History and Behavior

Behavior

Perception Channels: tactile ; chemical

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Life Expectancy

Average lifespan

Status: captivity:
12.5 years.

Average lifespan

Status: wild:
30.0 years.

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Lifespan, longevity, and ageing

Maximum longevity: 40 years (captivity) Observations: Manatees may feature some form of continuous tooth development (Caleb Finch 1990). It is estimated that they can live 30 years in the wild (David Macdonald 1985), but probably longer. One wild born specimen was still alive in captivity at 40 years of age (Richard Weigl 2005).
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Reproduction

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.

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Conservation

Conservation Status

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

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IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A3cd

Version
3.1

Year Assessed
2008

Assessor/s
Marmontel, M.

Reviewer/s
Reynolds III, J.E. & Powell, J.A. (Sirenia Red List Authority)

Contributor/s

Justification
Trichechus inunguis is here listed as Vulnerable based on a suspected population decline of at least 30% within the next three generations (assuming a generation length of 20 years, based on what is known for T. manatus) due primarily to ongoing levels of hunting, sometimes involving new and sophisticated techniques, coupled with increasing incidental calf mortality, climate change and habitat loss and degradation.

History
  • 2007
    Vulnerable
  • 1996
    Vulnerable
  • 1994
    Vulnerable
    (Groombridge 1994)
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Vulnerable
    (IUCN Conservation Monitoring Centre 1986)
  • 1982
    Vulnerable
    (Thornback and Jenkins 1982)
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Current Listing Status Summary

Status: Endangered
Date Listed: 06/02/1970
Lead Region: Foreign (Region 10) 
Where Listed: Entire


Population detail:

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

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Status

Classified as Vulnerable (VU A1cd) on the IUCN Red List (1), listed on Appendix I of CITES (4), and listed as Endangered by the US Endangered Species Act. (5). The Amazonian manatee also has a Global Heritage Status Rank of G2 (5).
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Population

Population
Most of the waters inhabited by Amazonian manatees are very murky, and, probably as an adaptation to past and ongoing hunting pressure, Amazonian manatees are extremely secretive. Consequently, there are no reliable population estimates available, although numbers are almost certainly lower than historical figures due to centuries of hunting. Husar (1977) estimated a minimum of 10,000 manatees for the entire Amazon basin, and Best (1983) estimated 500 to 1,000 in Amanã Lake (45 x 3 km) alone in 1979, but these numbers must be regarded with caution since they are supported by very little empirical data. Analysis of feeding patches, sightings and interview surveys have been used to try to estimate population numbers (Soini 1995, Kendall et al. 2005) with limited results. Traditional mark-recapture studies are not appropriate due to the species’ secretive nature.

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 Picanço (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 Uatumã 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 Fundación Omacha started its work in the area of Puerto Nariño, 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 Ecuador’s 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.

Population Trend
Decreasing
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Threats

Major Threats
The major threats to the species include hunting for food, incidental capture in gill nets, and habitat degradation.

Hunting
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 Airão, Tefé, 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 Picanço pers. comm. 2005, Hage pers. comm. 2005). A 60-l can of mixira sells for approximately U$168 (Lazzarini and Picanço 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 (‘batição’) 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 Picanço 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 Picanço 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 Omacha’s research) for very limited areas (Table 1).

Follow the link below 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 Nariño (Zaragoza to Atacuari) (Kendall et al. 2005). In the Puerto Nariño 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 “poço” (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 Picanço 2005). During the drought of 1998, multiple numbers of manatees were taken in one day in three different “poços” of the Coari town (AM) area (16 in the Poço 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 Picanço 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 Preservação e Pesquisa de Mamíferos Aquáticos) 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, Picanço 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 Belém-Santarém 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 manatee’s 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. Proaño 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.
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Once known to occur in large herds and have healthy populations (2), the Amazonian manatee has suffered from extensive hunting by subsistence and commercial hunters. It has been sought for meat, oil and fat, and at one time for its hide, which was in demand for use as water hoses and machine belts (7). Threats now include hunting and accidental drowning in commercial fishing nets. The deforestation of large areas of the forests surrounding this manatee's river habitats has also caused soil erosion, degradation of food supplies and the reduction of vegetation in the waterways (7).
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Management

Conservation Actions

Conservation Actions
Listed on Appendix I of CITES. Presently there are no national management plans specific for the species, except in Colombia. Management plans exist for two protected areas (Pacaya Samiria in Peru and Mamiraua Reserve in Brazil), and two communities in Colombia (Puerto Narino and Mocagua) have informal local management agreements (Ministerio de Ambiente, Vivienda y Desarrollo Territorial and Fundación Omacha 2005). Amazonian Manatees have been recorded from two protected areas in Ecuador, two in Colombia, four in Peru and 23 in Brazil. Unfortunately, hunting continues even within protected areas.

Presently, INPA (Instituto Nacional de Pesquisas da Amazônia) 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-Chão (PA, Brazil) has rescued six orphans (two of which died) and a sick adult manatee (Luna 2005 pers. comm.).
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Conservation

International trade of this species is prohibited due to its listing on Appendix I of CITES (4). This species has suffered huge losses but is locally abundant in the more remote regions of the Amazonian River Basin. However, it is very difficult to control hunting in these economically depressed areas and they are still killed for meat (3). While numerous federal, state, and local conservation measures are in place to protect the Florida manatee (T. manatus latirostris), South America has limited resources for funding comprehensive conservation projects. Several effective programs in Brazil include surveys by Projeto Peixe-Boi/Center for Aquatic Mammals (14), sustainable use research by Mamirauá Project (15), and education/outreach efforts by The Friends of the Manatee Association (16). The Harbour Branch Division of Marine Mammal Research and Conservation conducts manatee conservation outreach programs in Brazil and plays an important role in rehabilitating injured, sick or orphaned individuals (12). It is hoped that these measures combined with stronger hunting laws will allow the ancient and wonderful Amazonian manatee to recover (12) (13).
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Relevance to Humans and Ecosystems

Benefits

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Manatees are a source of food for many native peoples.

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Wikipedia

Amazonian manatee

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, Colombia and Ecuador.[2] It has thin, wrinkled skin, and is almost hairless, but has "whiskers" around its mouth.[3] It also has a distinct white breast patch, with fine hairs scattered over its body.[4] It may also be known as Amazon Manatee sea cow.[5]

Recently, a closely related, but far smaller species, the dwarf manatee (Trichechus pygmaeus), has been described from Brazil by Marc van Roosmalen.[6] Its validity has later been questioned, with some believing it to be an immature Amazonian manatee.[6]The Amazonian manatee is the second-smallest species of manatee after the recently discovered dwarf manatee. [6]

Taxonomy[edit]

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. [7]


Physical Characteristics[edit]

It is the only sirenian that exclusively lives in freshwater habitat.[8] Amazonian manatees rely 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.[9] Amazonian manatees (and manatees in general) are also found to be able to make long dives relative to other marine animals (up to 16 minutes in length), however these animals were restrained and when retested on free-diving individuals, the results showed less long-term diving (from 5 seconds to 10 minutes) dependent upon metabolic factors.[10]

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.[11] 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. [11] The manatee's upper lip is modified into a large bristly surface, which is deeply divided. [11] It can move each side of the lips independently while feeding. [11]The general coloration is gray, and most Amazonian manatees have a distinct white or bright pink patch on the breast.[11]

The manatee does not have incisors or canine teeth, only cheek teeth (molars). [11]Molars designed to crush vegetation form continuously at the back of the jaw and move forward as older ones wear down. [11]The older ones eventually fall out, while new ones come in at the rear of the jaw to replace them.[11]


Unique Features[edit]

A feature of the Amazonian manatee is its lack of nails on its flippers, setting it apart from other manatees.[7]

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. Another unique feature to the Amazonian Manatee, as well as the Florida Manatee, is vocalization: Both species have been seen to vocalize both alone and to each other, particularly between cows and their calves.[12]


Body Size[edit]

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 –230.0cm for free-ranging manatees, respectively.[13] The maximum actual Amazonian manatee weight reported is 379.5 kg.[13]

Amazonian manatee calves are born weighing 10–15 kg and 85 –105 cm long. [13]


Behavior and Biology[edit]

Manatees surface for air about every 40 minutes. [14] The longest documented submergence of an Amazonian manatee in captivity is 14 minutes [14]

Manatees make seasonal movements synchronized with the flood regime of the Amazon Basin.[15] They are found in flooded forests and meadows during the flood season, when food is abundant.[15] The Amazonian manatee has the smallest degree of rostral deflection (25° to 41°) among sirenians.[16] According to anatomical evidence, this is an adaptation of this species to feed closer to the water surface.[16]

This animal is both nocturnal and diurnal and lives its life almost entirely underwater.[17] Only its nostrils protrude from the surface of the water as this animal searches river and lake bottoms for lush vegetation.[17]


Diet[edit]

The manatees themselves feed on a variety of aquatic macrophytes, including aroids, grasses, bladderwarts, hornworts, water lilies, and particularly, water hyacinths. [18] Maintaining an herbivorous diet, the manatee has a similar post-gastric digestive process to that of the horse.[16] The manatee consumes approximately 8% of its body weight in food per day.[16]

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.[15] 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.[15]


Population and Distribution[edit]

As of 1977 the population count of the Amazonian Manatee was estimated to be around 10,000.[19] As of now the total population count is undetermined, however the population trend seems to be decreasing.[19] 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.[19] They are occasionally found overlapping with the West Indian Manatee along the coasts of Brazil.[19]


Reproduction and Lifecycle[edit]

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.[20] After the calf is born, it will begin to eat while staying with its mother for 12 - 18 months.[5]

Two individual manatees, in captivity, lived 12.5 years. [11]

Wild individuals have a lifespan of about 30 years. [17]


Evolution[edit]

The Amazonian's order Sirenia is closely related to other hoofed mammals called the Tethytheria which include the orders Desmostylia and Embrithopoda, the former being a hippopotamus-like marine mammal and the latter being rhinoceros-like. It is proposed that the Sirenians most likely branched off from these distant relatives during the Palaeocene era 65-54 million years ago, eventually migrating from land to water.[21]

Habitat[edit]

It is the only manatee to occur exclusively in freshwater environments.[22] The Amazonian manatee favors backwater lakes, oxbows, and lagoons with deep connections to large rivers and abundant aquatic vegetation [22]They are mainly solitary but sometimes they will gather in small groups consisting of up to 8 individuals.[23] These Individuals engage in long seasonal movements, moving from flooded areas during the wet season to deep water-bodies during the dry season[24]


Geography[edit]

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.[24] However, they are patchily distributed, concentrating in areas of nutrient-rich flooded forest, which covers around 300,000 km² [24] 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[24]


Ecology[edit]

The Amazonian manatee is completely aquatic and never leaves the water.[15]


Predation[edit]

Natural predators include jaguars, sharks, and crocodiles.[17]


Causes of Endangerment[edit]

Hunting remains the largest problem and continues in much of its range, even within reserves.[2] 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.[25] While hunting still occurs, an increasing risk to its continued survival in Ecuador is now believed to be the risk of oil spills.[2] The oil exploration also means an increase in boat traffic on the rivers.[2]

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. [14] Such hunting is carried out with harpoons, gillnets, and set traps. [14] Much of this hunting occurs in the lakes and streams near the Pacaya-Samiria National Reserve in northeastern Peru. [14]The species is slow-moving, docile, and is often found feeding at the surface of the lakes and rivers it inhabits. [15]Manatees are also at risk from pollution, accidental drowning in commercial fishing nets, and the degradation of vegetation by soil erosion resulting from deforestation.[15] Additionally, the indiscriminate release of mercury in mining activities threatens the entire aquatic ecosystem of the Amazon Basin.[15]

The manatee has been protected by Peruvian law since 1973, via Supreme Decree 934-73-AG, prohibiting hunting and commercial use of the manatee. [14]


Current status[edit]

The IUCN red list ranks the Amazonian manatee as vulnerable. Current population declines are primarily a result of hunting, as well as calf mortality, climate change, and habitat loss.[2] However, due to their murky water habitat it is difficult to gain accurate population estimates.[2]


Conservation Actions[edit]

There are no national management plans for the Amazonian Manatee, except in Colombia.[2] Currently, the INPA takes care of 34 captive manatees and the CPPMA is caring for 31 manatees.[2]


See also[edit]

References[edit]

  1. ^ Shoshani, J. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 93. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  2. ^ a b c d e f g h i Marmontel, M. (2008). Trichechus inunguis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 29 December 2008.
  3. ^ conserve nature manatee site
  4. ^ Trichechus inunguis Sandra L. Husar Mammalian Species , No. 72, Trichechus inunguis (Jun. 15, 1977), pp. 1-4 Published by: American Society of Mammalogists Article Stable URL: http://www.jstor.org/stable/3503928
  5. ^ a b "Amazonian Manatee". theanimalfiles.com. theanimalfiles.com. Retrieved 24 October 2014. 
  6. ^ a b c Trials of a Primatologist. - smithsonianmag.com. Accessed March 16, 2008.
  7. ^ a b "Manatees". http://www.conservenature.org/. Institute for the Study of Human-Animal Relations. Retrieved 21 October 2014. 
  8. ^ Amaral R.S., V.M.F da Silvia, and F.C.W Rosas. 2010. Body weight/length relationship and mass estimation using morphometric measurements in Amazonian manatees Trichechus inunguis Mammalia: Sirenia. Marine Biodiversity Records. 3:e105-e109.
  9. ^ Gallican G.J., R.C. Best, and J.W. Kanwisher. 1982. Temperature regulation in the amazonian manatee trichechus inunguis. Physiological zoology The university of chicago press 255-262.
  10. ^ Metabolism and Respiration of the Amazonian Manatee (Trichechus inunguis) G. J. Gallivan and R. C. Best Physiological Zoology , Vol. 53, No. 3 (Jul., 1980), pp. 245-253 Published by: The University of Chicago Press Article Stable URL: http://www.jstor.org/stable/30155787
  11. ^ a b c d e f g h i "Animal Info - Amazonian Manatee". http://www.animalinfo.org/. animalinfo.org. Retrieved 23 October 2014. 
  12. ^ Evoked Brain Potentials Demonstrate Hearing in a Manatee (Trichechus inunguis) Theodore H. Bullock, Daryl P. Domning and Robin C. Best Journal of Mammalogy , Vol. 61, No. 1 (Feb., 1980), pp. 130-133 Published by: American Society of Mammalogists Article Stable URL: http://www.jstor.org/stable/1379969
  13. ^ a b c Amaral, Rodrigo S. (27 October 2010). "Body weight/length relationship and mass estimation using morphometric measurements in Amazonian manatees Trichechus inunguis (Mammalia: Sirenia)". Marine Biodiversity Records 3 (e105): 4. Retrieved 24 October 2014. 
  14. ^ a b c d e f contentReeves, Randall R.; Leatherwood, Stephen; Jefferson, Thomas A.; Curry, Barbara E.; Henningsen, Thomas. "Amazonian Manatees, Tricheus inunguis, In Peru: Distribution, Exploitation, and Conservation Status". https://swfsc.noaa.gov. Retrieved 20 October 2014. 
  15. ^ a b c d e f g h "70. Amazonian Manatee (Trichechus inunguis)". edgeofexistence.org. Zoological Society of London. Retrieved 22 October 2014. 
  16. ^ a b c d Pazin-Guterres, Michelle (2014). "Feeding Ecology of the Amazonian Manatee (Trichechus inunguis) in the Mamirauá and Amanã Sustainable Development Reserves, Brazil.". Aquatic Mammals 40 (2): 139–149. 
  17. ^ a b c d Gorog, Antonia. "Trichechus inunguis Amazonian manatee". animaldiversity.ummz.umich.edu. University of Michigan. Retrieved 22 October 2014. 
  18. ^ Ecology, Distribution, Harvest, and Conservation of the Amazonian Manatee Trichechus inunguis in Ecuador Robert M. Timm, Luis Albuja V. and Barbara L. Clauson Biotropica , Vol. 18, No. 2 (Jun., 1986), pp. 150-156 Published by: The Association for Tropical Biology and Conservation Article Stable URL: http://www.jstor.org/stable/2388757
  19. ^ a b c d "Amazonian manatee distribution and population". http://www.edgeofexistence.org/. Retrieved 24 October 2014. 
  20. ^ Seasonal Breeding in the Amazonian Manatee, Trichechus inunguis (Mammalia: Sirenia) Robin C. Best Biotropica , Vol. 14, No. 1 (Mar., 1982), pp. 76-78 Published by: The Association for Tropical Biology and Conservation Article Stable URL: http://www.jstor.org/stable/2387764
  21. ^ "Evolution of the Sirenia: An Outline". http://www.sirenian.org/. Retrieved 24 October 2014. 
  22. ^ a b http://www.arkive.org/amazonian-manatee/trichechus-inunguis/
  23. ^ http://www.theanimalfiles.com/mammals/dugong_manatees/amazonian_manatee.html
  24. ^ a b c d http://www.iucnredlist.org/details/summary/22102/0
  25. ^ Ecology, Distribution, Harvest, and Conservation of the Amazonian Manatee Trichechus inunguis in Ecuador. Robert M. Timm, Luis Albuja V. and Barbara L. Clauson. Biotropica , Vol. 18, No. 2 (Jun., 1986), pp. 150-156. Published by: The Association for Tropical Biology and Conservation. Article Stable URL: http://www.jstor.org/stable/2388757
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