Ariranha, Lontra-gigante ou Lobo-do-rio (Pteronura brasiliensis) - Giant Otter - 22-11-2009 - IMG_6873

The following text, in english, is from Wikipedia, the free encyclopedia:

The Giant Otter (Pteronura brasiliensis) is a South American carnivorous mammal. It is the longest member of the Mustelidae, or weasel family, a globally successful group of predators. Unusually for a mustelid, the Giant Otter is a social species, with family groups typically supporting three to eight members. The groups are centered on a dominant breeding pair and are extremely cohesive and cooperative. Although generally peaceful, the species is territorial and aggression has been observed between groups. The Giant Otter is diurnal, being active exclusively during daylight hours. It is the noisiest otter species and distinct vocalizations have been documented that indicate alarm, aggressiveness, and reassurance. The Giant Otter ranges across north-central South America.

Its distribution has been greatly reduced and is now discontinuous. Decades of poaching for its velvety pelt, peaking in the 1950s and 1960s, hugely diminished population numbers. The species was listed as endangered in 1999 and population estimates are typically below 5,000 in the wild. The Guianas are the last real stronghold for the species. It is the most endangered mammal in the neo-tropics. Habitat degradation and loss is the greatest current threat. The Giant Otter is also rare in captivity: as of 2003, only 60 animals were held.[3]

The Giant Otter shows a variety of adaptations suitable to an amphibious lifestyle, including exceptionally dense fur, a wing-like tail, and webbed feet. The species prefers freshwater rivers and streams, which are usually seasonally flooded, and may also take to freshwater lakes and springs. It constructs extensive campsites close to feeding areas, clearing large amounts of vegetation. The Giant Otter largely subsists on a diet of fish, particularly characins and catfish, and may also eat crabs. It has no serious natural predators other than humans, although it must compete with other species, including the Neotropical Otter and caiman species, for food resources.

Naming:

The Giant Otter has a handful of other names in English. River Wolf (Spanish: Lobo del Río) and Water Dog (Spanish: Perro del Agua) are used occasionally. The last of these may have been more common in the reports of explorers in the nineteenth and early twentieth centuries.[4] All three names are in use in Spanish and Portuguese, with a number of regional variations. "Giant Otter" translates as Nutria Gigante and Lontra Gigante in Spanish and Portuguese, respectively; a fourth name, Ariraí or Ariranha is also in use in South America.[5] Among the Achuar people, they are known as Wankanim,[6] and among the Sanumá as Hadami.[7][8] The genus name, Pteronura, is derived from the Ancient Greek words pteron/πτερον 'feather' or 'wing' and ura/ουρά 'tail',[9] a reference to its distinctive wing-like tail.[10]

Taxonomy and evolution:

The otters form the Lutrinae subfamily within the mustelids and the Giant Otter is the only member of the genus Pteronura. Two subspecies are currently recognized by the canonical Mammal Species of the World, P. b. brasiliensis and P. b. paraguensis. Incorrect descriptions of the species have led to multiple synonyms (the latter subspecies is often P. b. paranensis in the literature).[1] P. b. brasiliensis is distributed across the north of the Giant Otter range, including the Orinoco, Amazon, and Guianas river systems; to the south, P. b. paraguensis has been suggested in Paraguay, Uruguay, southern Brazil, and northern Argentina,[5] although it may be extinct in the last three of these four. The World Conservation Union (IUCN) considers the species' presence in Argentina and Uruguay uncertain.[2] In the former, investigation has shown thinly distributed population remnants.[11] P. b. paraguensis is supposedly smaller and more gregarious, with different dentition and skull morphology. Carter and Rosas, however, rejected the subspecific division in 1997, noting that the classification had only been validated once, in 1968, and that the P. b. paraguensis type specimen was very similar to P. b. brasiliensis.[12] Biologist Nicole Duplaix calls the division of "doubtful value."[13]

An extinct genus, Satherium, is believed to be ancestral to the present species, having migrated to the New World during the Pliocene or early Pleistocene.[10] The Giant Otter shares the South American continent with three of the four members of the Lontra genus of otters: the Neotropical River Otter, the Southern River Otter, and the Marine Otter.[14] It seems to have evolved independently of Lontra in South America, despite the overlap. The Smooth-coated Otter (Lutrogale perspicillata) of Asia may be its closest extant relative: similar behaviour, vocalizations, and skull morphology have been noted.[10] Both species also show strong pair bonding and paternal engagement in rearing cubs.[15]

Phylogenetic analysis by Koepfli and Wayne in 1998 found that the Giant Otter has the highest divergence sequences within the otter subfamily, forming a distinct clade that split away 10 to 14 million years ago. They noted that the species may be the basal divergence among the otters or fall outside of them altogether, having split even before other mustelids, such as the Ermine, Polecat, and Mink.[10] Later gene sequencing research on the mustelids, from 2005, places the divergence of the Giant Otter somewhat later, between 5 and 11 million years ago; the corresponding phylogenetic tree locates the Lontra divergence first amongst otter genera, and Pteronura second, although divergence ranges overlap.[16]

Biology and behaviour:

The Giant Otter is large, gregarious, and diurnal (active through the day). Early travellers' reports describe noisy groups surrounding explorers' boats but little scientific information was available on the species until Duplaix's groundbreaking work in the late 1970s.[17] Concern over this endangered species has since generated a corpus of research.

Physical characteristics:

The Giant Otter is clearly distinguished from other otters by morphological and behavioural characteristics. It has the greatest body length of any species in the mustelid family, although the Sea Otter may be heavier. Males are between 1.5 and 1.8 meters (4.9–5.9 feet) in length and females between 1.5 and 1.7 m (4.9–5.6 ft). The animal's well-muscled tail can account for as much as 69 centimeters (27 in) of total body length.[18] Early reports of skins and living animals suggested exceptionally large males of up to 2.4 m (7.9 ft); intensive hunting likely reduced the occurrence of such massive specimens. Weights are between 32 and 45.3 kilograms (70–100 pounds) for males and 22 and 26 kg (48–57 lbs) for females.[19]

The Giant Otter has the shortest fur of all otter species; it is typically chocolate brown but may be reddish or fawn, and appears nearly black when wet.[19] The fur is extremely dense, so much so that water cannot penetrate to the skin.[20] Guard hairs trap water and keep the inner fur dry; the guard hairs are approximately 8 millimeters (one third of an inch) in length, about twice as long as the fur of the inner coat.[21] Its velvety feel makes the animal highly sought after by fur traders and has contributed to its decline.[22] Unique markings of white or cream fur color the throat and under the chin, allowing individuals to be identified from birth.[19]

Giant Otter muzzles are short and sloping and give the head a ball-shaped appearance.[13] The ears are small and rounded.[20] The nose (or rhinarium) is completely covered in fur, with only the two slit-like nostrils visible. The Giant Otter's highly sensitive whiskers (vibrissae) allow the animal to track changes in water pressure and currents, which aids in detecting prey.[23] The legs are short and stubby and end in large webbed feet tipped with sharp claws. Well suited for an aquatic life, it can close its ears and nose while underwater.[24]

As of Carter and Rosas' writing, vision had not been directly studied but field observations show that the animal primarily hunts by sight; above water, it is able to recognize observers at great distances. The fact that it is exclusively active during the day further suggests its eyesight should be strong, to aid in hunting and predator avoidance. In other otter species vision is generally normal or slightly myopic, both on land and in water. The Giant Otter's hearing is acute and its sense of smell excellent.[25][19]

Vocalizations:

The Giant Otter is an especially noisy animal, with a complex repertoire of vocalizations. All otters produce vocalizations, but by frequency and volume, the Giant Otter may be the most vocal.[26] Duplaix identified nine distinct sounds, with further subdivisions possible, depending on context. Quick HAH! barks or explosive snorts suggest immediate interest and possible danger. A wavering scream may be used in bluff charges against intruders, while a low growl is used for aggressive warning. Hums and coos are more reassuring within the group. Whistles may be used as advance warning of non-hostile intent between groups, although evidence is limited. Newborn cubs squeak to elicit attention, while older young whine and wail when they begin to participate in group activities.[27]

Social structure:

The Giant Otter is a highly social animal and lives in extended family groups. Group sizes are anywhere from two to twenty members but likely average between three and eight.[5] (Larger figures may reflect two or three family groups temporarily feeding together.)[28] The groups are strongly cohesive: the otters sleep, play, travel, and feed together.

Group members share roles, structured around the dominant breeding pair. The species is territorial, with groups marking their ranges with latrines, gland secretions, and vocalizations.[29] At least one case of a change in alpha relationship has been reported, with a new male taking over the role; the mechanics of the transition were not determined.[30] Duplaix suggests a division between residents, who are established within groups and territories, and nomadic and solitary transients; the categories do not seem rigid, and both may be a normal part of the Giant Otter life cycle.[31] One tentative theory for the development of sociality in mustelids is that locally abundant but unpredictably dispersed prey causes groups to form.[32]

Aggression within the species ("intraspecific" conflict) has been documented. Defense against intruding animals appears to be cooperative: while adult males typically lead in aggressive encounters, cases of alpha females guarding groups have been reported.[30] One fight was directly observed in the Brazilian Pantanal in which three animals violently engaged a single individual near a range boundary.[29] In another instance in Brazil, a carcass was found with clear indications of violent assault by other otters, including bites to the snout and genitals, an attack pattern similar to that exhibited by captive animals.[33] While not rare amongst large predators in general, intraspecific aggression is uncommon amongst otter species; Ribas and Mourão suggest a correlation to the animal's sociability, which is also rare amongst other otters.[29] A capacity for aggressive behaviour should not be overstated with the Giant Otter. Researchers emphasize that even between groups, conflict avoidance is generally adopted.[34][35] Within groups, the animals are extremely peaceful and cooperative. Group hierarchies are not rigid and the animals easily share roles.[36]

Reproduction and life cycle:

Details of Giant Otter reproduction and life cycle are scarce, and captive animals have provided much of the information. Females appear to give birth year round, although in the wild births may peak during the dry season. The estrous cycle is 21 days, with females receptive to sexual advances between 3 and 10 days.[37] Study of captive specimens has found that only males initiate copulation.[3] At Tierpark Hagenbeck in Germany, long-term pair bonding and individualized mate selection were seen, with copulation most frequently taking place in water.[38] Females have a gestation period of 65 to 70 days, giving birth to one to five pups, with an average of two.[38][37] Research over five years on a breeding pair at the Cali Zoo in Colombia found that the average interval between litters was six to seven months, but as short as 77 days when the previous litter did not survive.[3] Other sources have found greater intervals, with as long as 21 to 33 months suggested for the wild.[37]

Mothers give birth to furred and blind cubs in an underground den near to the river shore and fishing sites.[39] Males actively participate in rearing cubs and family cohesion is strong;[40] older, juvenile siblings also participate in rearing, although in the weeks immediately after birth they may temporarily leave the group.[37] Cubs open their eyes in their fourth week, begin walking in their fifth, and are able to swim confidently between 12 and 14 weeks.[3] They are weaned by nine months and begin hunting successfully soon after.[37] The animal reaches sexual maturity at about two years of age and both male and female cubs leave the group permanently after two to three years.[38][37] They then search for new territory to begin a family of their own.[41]

The Giant Otter is very sensitive to human activity when rearing its young. No institution, for example, has successfully raised Giant Otter cubs unless parents were provided sufficient privacy measures; the stress caused by human visual and acoustic interference can lead to neglect, abuse and infanticide, as well as decreased lactation. In the wild, it has been suggested, although not systematically confirmed, that tourists cause similar stresses: disrupted lactation and denning, reduced hunting, and habitat abandonment are all risks.[41] This sensitivity is matched by a strong protectiveness towards the young. All group members may aggressively charge intruders, including boats with humans in them.[42]

The longest documented Giant Otter lifespan in the wild is eight years. In captivity this may increase to 17, with an unconfirmed record of 19. The animal is susceptible to a variety of diseases, including the canine parvovirus. Parasites, such as the larvae of flies and a variety of intestinal worms, also afflict the Giant Otter.[41] Other causes of death include accidents, gastroenteritis, infanticide, and epileptic seizures.[37]

Hunting and diet:

The Giant Otter is an apex predator and its population status reflects the overall health of riverine ecosystems.[43] It feeds mainly on fish, including cichlids, characins (such as piranha), catfish, and perch. One full year study of Giant Otter scats in Amazonian Brazil found fish present in all fecal samples. Fish from the order Perciformes, particularly cichlids, were seen in 97% of scats, and Characiformes, such as characins, in 86%. Fish remains were of medium-sized species that seem to prefer relatively shallow water, to the advantage of the probably visually oriented Giant Otter. Prey species found were also sedentary, generally swimming only short distances, which may aid the Giant Otter in predation. The Giant Otter seems to be opportunistic, taking whatever species are most locally abundant.[44] If fish are unavailable it will also take crabs, snakes, and even small caimans and anacondas.[45]

The species can hunt singly, in pairs, and in groups, relying on its sharp eyesight to locate prey.[46] In some cases, supposed cooperative hunting may be incidental, a result of group members fishing individually in close proximity; truly coordinated hunting may only occur where the prey cannot be taken by a single Giant Otter, such as with anacondas and the Black Caiman.[35] The Giant Otter seems to prefer prey fish that are generally immobile on river bottoms in clear water. Prey chase is rapid and tumultuous, with lunges and twists through the shallows and few missed targets. The otter can attack from both above and below, swiveling at the last instant to clamp the prey in its jaws. Giant Otters catch their own food and consume it immediately; they grasp the fish firmly between the forepaws and begin eating noisily at the head.[46] Carter and Rosas have found that captive adult animals consume around 10% of their body weight daily—about 3 kilograms (7 lb), in keeping with findings in the wild.[47]

Habitat:

The species is amphibious, although primarily terrestrial.[48] It is found in freshwater rivers and streams, which are generally seasonally flooded. Other water habitats include freshwater springs and permanent freshwater lakes.[2] Four specific vegetation types were found on one important creek in Suriname: riverbank high forest; floodable mixed marsh and high swamp forest; floodable low marsh forest; and grass islands and floating meadows within open areas of the creek itself.[48] Duplaix identifies two critical factors in habitat selection: food abundance, which appears to positively correlate to shallow water, and low sloping banks with good cover and easy access to preferred water types. The Giant Otter seems to choose clear black waters with rocky or sandy bottoms over silty, saline, and white waters.[49]

Areas adjacent to rivers are used for the construction dens, campsites, and latrines.[50] Giant Otters clear significant amounts of vegetation in constructing their campsites. One report suggests maximum areas 28 m (92 ft) long and 15 m (49 ft) wide, well-marked by scent glands, urine, and feces to signal territory.[14] Carter and Rosas find average areas a third this size. Communal latrines are adopted adjacent to the campsites, and dens with a handful of entrances are dug, typically under root systems or fallen trees. One report found between three and eight campsites, clustered around feeding areas. In seasonally flooded areas, the Giant Otter may abandon campsites during the wet season, dispersing to flooded forests in search of prey.[51] Preferred locations may be adopted perennially, often on high ground. These can become quite extensive, including "backdoor" exits into forests and swamps, away from the water.[48] Not every site is visited or marked daily, but all are usually patrolled, often by a pair of otters in the morning.[52]

Research generally takes place in the dry season and an understanding of the species' overall habitat use remains partial. Dry season range size analysis of three otter groups in Ecuador found areas between 0.45 and 2.79 square kilometres (0.17 and 1.08 sq mi). Habitat requirements and availability were presumed to be dramatically different in the rainy season: range sizes of 1.98 to as much as 19.55 square kilometres (0.76 to 7.55 sq mi) were estimated for the groups.[50] Other researchers suggest approximately 7 square kilometres (2.7 sq mi) and note a strong inverse correlation between sociality and home range size; the highly social Giant Otter has smaller home range sizes than would be expected for a species of its mass.[32] Population densities varied with a high of 1.2 /km2 (3.1 /sq mi) reported in Suriname and with a low of 0.154 /km2 (0.40 /sq mi) found in Guyana.[5]

Predation and competition:

Adult Giant Otters have no serious natural enemies, beyond human beings. "Possible and occasional" predation by the Jaguar, Cougar, and anacondas has been suggested by Duplaix, but based on historical reports, not direct observation.[53] Cubs are more vulnerable, and may be taken by the Black Caiman and other large predators,[41] although adults are constantly mindful of stray young. The Spectacled Caiman is another potential competitor, but Duplaix found no conflict with the species in Suriname. When in the water, the Giant Otter faces danger from animals that are not strictly preying upon it: the Electric eel and stingrays are potentially deadly if stumbled upon, and piranha may be capable of at least taking bites out of a Giant Otter, as evidenced by scarring on individuals.[54]

Even if without direct predation, the Giant Otter must still compete with other predators for food resources. Duplaix documented interaction with the Neotropical Otter.[55] While the two species are sympatric (with overlapping ranges) during certain seasons, there appeared to be no serious conflict. The smaller Neotropical Otter is far more shy, less noisy, and less social; at about a third the weight of the Giant Otter, it is more vulnerable to predation and, hence, a lack of conspicuousness is to its advantage. The Neotropical Otter is active during twilight and darkness, reducing the likelihood of conflict with the diurnal Giant Otter.[56] Its smaller prey, different denning habits, and different preferred water types also reduce interaction.[47]

Other species that prey upon similar food resources include the caimans and large fish that are themselves piscivores. Gymnotids, such as the Electric Eel, and the large Silurid catfish are among aquatic competitors. Two river dolphins, the Tucuxi and Boto, might potentially compete with the Giant Otter but different spatial use and dietary preferences suggest minimal overlap.[47]

Conservation status:

The IUCN listed the Giant Otter as "endangered" in 1999; it had been considered "vulnerable" under all previous listings from 1982 when sufficient data had first become available. It is regulated internationally under Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES): all trade in specimens and parts is illegal.[57]

 

Ariranha, Lontra Gigante ou Lobo-do-rio (Pteronura brasiliensis).

O texto, em português, a seguir, é da wikipédia:

A ariranha, lontra-gigante (do inglês Giant Otter) ou lobo-do-rio (Pteronura brasiliensis), é um mamífero mustelídeo, característico do Pantanal e da bacia do Rio Amazonas.

A ariranha é a maior espécie da sub-família Lutrinae (as lontras) e pode chegar a medir cerca de 180 centímetros de comprimento, dos quais 65 compõem a cauda. Os machos são geralmente mais pesados que as fêmeas e pesam até 26 kg. A ariranha têm olhos relativamente grandes, orelhas pequenas e arredondadas, patas curtas e espessas e cauda comprida e achatada. Os dedos das patas estão unidos por membranas interdigitais que facilitam a natação. A pelagem é espessa, com textura aveludada e cor escura, excepto na zona da garganta onde apresentam uma mancha branca.

A ariranha vive e caça em grupos que podem chegar aos dez indivíduos e alimenta-se dos peixes, que habitam os rios da América do Sul, principalmente de caracídeos como a piranha e a traíra. Ingere-os sempre com a cabeça fora d'água, freqüentemente nadando pitorescamente para trás. Em condições de escassez, os grupos caçam pequenos jacarés e cobras, que podem inclusive ser pequenas anacondas. No seu habitat, as ariranhas adultas são predadores de topo da cadeia alimentar.

A época do acasalamento é na estação das chuvas, que pode ir de janeiro a março e resulta em gestações de 65 a 72 dias. Apenas a fêmea dominante do grupo se reproduz. Entre maio e setembro, as fêmeas dão à luz uma ninhada de pequenas lontras que são educadas em conjunto por todo o grupo. As crias ficam numa toca durante os primeiros três meses, após o que são integradas na vida do grupo. As ariranhas atingem a maturidade sexual entre os dois e os três anos de vida.

É uma espécie em perigo e a principal ameaça à sua sobrevivência é o desmatamento e destruição do seu habitat. A poluição dos rios, principalmente junto de explorações mineiras causam vítimas entre as lontras que se alimentam de peixe contaminado por metais, que se acumulam nos peixes e mais intensamente ainda nas ariranhas que estão no topo da cadeia alimentar. Entre os metais o que mais freqüentemente contamina animais é o mercúrio, usado na extração de ouro. Há também algumas perdas devidas a caça furtiva por causa da pele, que foi mais intensa no passado.

Os primeiros sucessos reprodutivos em cativeiro foram produzidos pela Fundação Zoológico de Brasília, onde os animais desfrutam de um ótimo recinto. A espécie protagonizou um episódio trágico no zoo: um militar, o Sargento do Exército Brasileiro Sílvio Delmar Hollenbach, atirou-se no recinto objetivando salvar um garoto que lá caíra, e apesar de ter concluído seu objetivo acabou morrendo dias depois, em virtude de uma infecção generalizada, causada pelas inúmeras mordidas.

[editar]Características

 

A ariranha é claramente distinguível das demais lontras pelas características morfológicas e comportamentais. Ela é o maior membro da família Mustelidae em comprimento, sendo a lontra-marinha a maior em peso. Os machos possuem de 1.5 a 1.8 metros de comprimento e as fêmeas de 1.5 a 1.7 metros. . O peso varia de 32 a 45.3 kilogramas para machos e de 22 a 26 kg para fêmeas.

[editar]Ataques a Humanos

 

Ataques registrados de Ariranhas são raros, a maioria ocorrido acidentalmente na região da bacia amazônica.

Porém em 1977 um ataque resultou na morte do Sargento Silvio Delmar Hollenbach no Jardim Zoológico de Brasília

[editar]Referências

 

Groenendijk, J., Hajek, F. & Schenck, C. 2004. Pteronura brasiliensis. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. (www.iucnredlist.org/search/details.php/18711/all). Salvo em 7 de janeiro de 2007.

 

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