The gharial (Gavialis gangeticus) is a crocodilian of the family Gavialidae that is native to the Indian subcontinent and also called gavial and fish-eating crocodile. As the species has undergone both chronic long term and a rapid short-term declines it is listed as a Critically Endangered by IUCN.The gharial is one of three crocodilians native to India, apart from the mugger crocodile and the saltwater crocodile. It is one of the longest of all living crocodilians.
Characteristics
Male gharial at the Madras
Crocodile Bank Trust
Gharial skeleton
As do all large crocodilians, the gharial starts out life fairly small. Hatchlings measure approximately long 37 cm (15 in). Young gharials can reach a length of 1 m (3.3 ft) in eighteen months. The average body weight of the species is from 159 to 250 kg (350 to 550 lb). Males commonly attain a total length of 3 to 5 m (9.8 to 16 ft), while females are smaller and reach a body length of up to 2.7 to 3.75 m (8.9 to 12.3 ft).
The three largest examples reported were a 6.5 m (21 ft) gharial killed in the Gogra River of Faizabad in August 1920; a 6.3 m (21 ft) individual shot in the Cheko River of Jalpaiguri in 1934; and a giant of 7 m (23 ft), which was shot in the Kosi River of northern Bihar in January 1924. Such exceptionally larger specimens can scale up to 977 kg (2,150 lb) in mass. While specimens of over 6 m (20 ft) were not uncommon in the past, such large individuals are not known to exist today. Gharials are exceeded in length only by the saltwater crocodile.
Gharials' well-developed laterally flattened tail and webbed rear feet provide tremendous manoeuvrability in their deepwater habitat. On land, however, an adult gharial can only push itself forward and slide on its belly. Further enhancing its swimming abilities, the body of the gharial is relatively cylindrical in shape, compared with the broader, more powerfully-built body of a saltwater or nile crocodile built for capturing various prey from the edges of waterways. The Gharial's elongated, narrow snout becomes proportionally shorter and thicker as an animal ages. The bulbous growth on the tip of a male’s snout renders gharials the only visibly sexually dimorphic crocodilian. This growth is present in mature individuals and called ghara after the Indian word meaning “pot”. Males utilize the structure to modify and amplify “hisses” snorted through the underlying nostrils. The resultant sound can be heard for nearly a kilometre on a still day. The ghara is thought to play an important role in gharial reproduction by identifying mature males to females and as an instrument in courtship auditory communication.
The Nepali word घड़ा ghaṛā means earthenware pot, pitcher, watervessel.
The leg musculature of the gharial does not enable it to raise its body off the ground to achieve the high-walk gait on land, but can only push its body forward across the ground ('belly-sliding'), although it can do this with some speed when required. However, when in water, the gharial is the most nimble and quick of all the crocodilians in the world. They can reach swimming speeds of at least 40 km/h (25 mph) while pursuing schools of fish. The jaws are lined with many interlocking, razor-sharp teeth — 27 to 29 upper and 25 or 26 lower teeth on each side. These teeth are not received into interdental pits; the first, second, and third mandibular teeth fit into notches in the upper jaw. The front teeth are the largest. The snout is narrow and long, with a dilation at the end and its nasal bones are comparatively short and are widely separated from the pre-maxillaries. The nasal opening of a gharial is smaller than the supra-temporal fossae. The lower anterior margin of orbit (jugal) is raised and its mandibular symphysis is extremely long, extending to the 23rd or 24th tooth. A dorsal shield is formed from four longitudinal series of juxtaposed, keeled, and bony scutes. The length of the snout is 3.5 (in adults) to 5.5 times (in young) the breadth of the snout's base. Nuchal and dorsal scutes form a single continuous shield composed of 21 or 22 transverse series. Gharials have an outer row of soft, smooth, or feebly keeled scutes in addition to the bony dorsal scutes. They also have two small post-occipital scutes. The outer toes are two-thirds webbed, while the middle toe is only one-third webbed. They have a strong crest on the outer edge of the forearm, leg, and foot. Typically, adult gharials have a dark olive colour tone while young ones are pale olive, with dark brown spots or cross-bands.
Distribution and habitat
Group of gharials and a mugger crocodile in the Karnali River of Bardia National Park, Nepal
Gharial lurking
Gharials once thrived in all the major river systems of the Indian subcontinent, spanning the rivers of its northern part from the Indus River in Pakistan across the Gangetic floodplain to the Irrawaddy River in Myanmar. Today, they are extinct in the Indus River, in the Brahmaputra of Bhutan and Bangladesh and in the Irrawaddy River. Their distribution is now limited to only 2% of their former range:
- In India, small populations are present and increasing in the rivers of the National Chambal Sanctuary, Katarniaghat Wildlife Sanctuary, Son River Sanctuary and the rainforest biome of Mahanadi in Satkosia Gorge Sanctuary, Orissa, where they apparently do not breed;
- In Nepal, small populations are present and slowly recovering in tributaries of the Ganges, such as the Narayani-Rapti river system in Chitwan National Park and the Karnali-Babai river system in Bardia National Park.
In 1977, four nests were recorded in the Girwa River of Katarniaghat Wildlife Sanctuary, where 909 gharials were released until 2006. Twenty nests were recorded in 2006, so 16 nesting females resulted from 30 years of reintroductions, which is equivalent to 2% of the total pre-2006 releases. This is seemingly not a great achievement for the money and effort spent, and as several knowledgeable researchers have suggested, perhaps carrying capacity has been reached there. In 1978, twelve nests were recorded in the Chambal River in the National Chambal Sanctuary, where 3,776 gharials were released until 2006. By 2006, nesting had increased by over 500% to 68 nests, but the recruited mature, reproducing females constituted only about 2% of the total number released. The newly hatched young are especially prone to being flushed downstream out of the protected areas during the annual monsoonal flooding.
Ecology and behavior
Gharials are arguably the most thoroughly aquatic of the extant crocodilians, and adults apparently do not have the ability to walk in a semi-upright stance as other crocodilians do. They are typically residents of flowing rivers with deep pools that have high sand banks and good fish stocks. Exposed sand banks are used for nesting.
Diet
Young gharials eat insects, larvae, and small frogs. Mature adults feed almost solely on fish, although some individuals have been known to scavenge dead animals. Their snout morphology is ideally suited for preying on fish. Their long, narrow snouts offer very little resistance to water in swiping motions to snap up fish in the water. Their numerous needle-like teeth are ideal for holding on to struggling, slippery fish. Gharials will often use their body to corral fish against the bank where they can be more easily snapped up.
Reproduction
The mating season is during November through December and well into January. The nesting and laying of eggs takes place in the dry season of March, April, and May. This is because during the dry season the rivers shrink a bit and the sandy river banks are available for nesting. Between 30 and 50 eggs are deposited into the hole that the female digs up before it is covered over carefully. After about 90 days, the juveniles emerge, although there is no record of the female assisting the juveniles into the water after they hatch (probably because their jaws are not suited for carrying the young due to the needle like teeth). However, the mother does protect the young in the water for a few days until they learn to fend for themselves.
Gharials and humans
Gharial
Unlike most crocodilians, the gharial is not a man-eater and tends to be very sensitive when intimidated by humans. Despite its immense size, its thin and fragile jaws render it physically incapable of consuming a large animal, especially a human being. The myth that gharials eat humans may come partly from their similar appearance to crocodiles and also since jewellery has been found in their stomachs. However, the gharial may have swallowed this jewellery while scavenging corpses or as gastroliths used to aid digestion or buoyancy management.
Threats
According to IUCN, there has been a population decline of 96–98% over a three-generation period since 1946, and the once widespread population of an estimated 5,000 to 10,000 individuals has been reduced to a very small number of widely spaced subpopulations of fewer than 235 individuals in 2006. The drastic decline in the gharial population can be attributed to a variety of causes including over-hunting for skins and trophies, egg collection for consumption, killing for indigenous medicine, and killing by fishermen. Hunting is no longer considered to be a significant threat. However, the wild population of gharials has undergone a drastic decline of about 58% within nine years between 1997 and 2006 due to:
- the increasing intensity of fishing and the use of gill nets, which is rapidly killing many of the scarce adults and many subadults — a threat prevalent throughout most of the present gharial habitat, even in protected areas;
- the excessive, irreversible loss of riverine habitat caused by the construction of dams, barrages, irrigation canals, siltation, changes in river course, artificial embankments, sand-mining, riparian agriculture, and domestic and feral livestock, which have combined to cause an extreme limitation to gharial range.
Conservation
Two gharials at San Antonio Zoo
Gavialis gangeticus is listed on CITES Appendix I. Conservation programs have been undertaken in India and Nepal, based on the establishment of protected areas and restocking these with animals born in captivity, but nowhere has restocking re-established viable populations. Over 5,000 juvenile gharials were released into largely inhospitable habitats in Indian and Nepali rivers and left to their fate. But reintroduction didn't work so well there largely due to growing and uncontrolled anthropogenic pressures, including depletion of the fish resources. Monitoring has not been consistently carried out, and little research on adaptation, migration and other key aspects has been conducted.
In situ initiatives
Gharial and Turtles
On 27 December 2010, the then Indian Minister for Environment and Forests, Jairam Ramesh, during a visit with Romulus Whitaker at the Madras Crocodile Bank announced the formation of a National Tri-State Chambal Sanctuary Management and Coordination Committee for gharial conservation on 1,600 km2 (620 sq mi) of the National Chambal Sanctuary along the Chambal River in Madhya Pradesh, Rajasthan and Uttar Pradesh. The Committee will comprise representatives of three states' Water Resources Ministries, states' Departments of Irrigation and Power, Wildlife Institute of India, Madras Crocodile Bank Trust, the Gharial Conservation Alliance, Development Alternatives, Ashoka Trust for Research in Ecology and the Environment, Worldwide Fund for Nature and the Divisional Forest officers of the three states. The Committee will plan strategies for protection of gharials and their habitat. This will involve further research on the species and its ecology and socio-economic evaluation of dependent riparian communities. Funding for this new initiative will be mobilized as a sub-scheme of the ‘Integrated Development of Wildlife Habitats’ in the amount of 50 to 80 million Indian Rupees (USD 1 million to 1.7 million) each year for five years. This project has long been advocated by Romulus Whitaker.
In captivity
Gharials are bred in captivity in the National Chambal Sanctuary in Uttar Pradesh, and in the Gharial Breeding Centre in Nepal's Chitwan National Park, where they are generally grown for two to three years and average about one meter, when released.
In India, they are also kept in the Madras Crocodile Bank Trust, Indira Gandhi Zoological Park, Jawaharlal Nehru Biological Park in Bokaro Steel City, Bannerghatta Zoo in Bangalore, Junagadh Zoo and Biological Park Itanagar. The National Zoological Gardens of Sri Lanka and the Singapore Zoo each keep a breeding pair. The Japanese Nogeyama Zoo keeps two females. In Europe, they are kept in the Prague Zoo. In the USA they are kept in the Honolulu Zoo, the Cleveland Metroparks Zoo, the Fort Worth Zoo, the San Diego Zoo, the National Zoological Park, the San Antonio Zoo and Aquarium and the St. Augustine Alligator Farm.
The French crocodile farm La Ferme aux Crocodiles received six juveniles in May 2000 from the Gharial Breeding Centre in Nepal.
Ancestry
The fossil history of the Gavialoidea is quite well known, with the earliest examples diverging from the other crocodilians in the late Cretaceous. The most distinctive feature of the group is the very long, narrow snout, which is an adaptation to a diet of small fish. Although gharials have sacrificed the great mechanical strength of the robust skull and jaw that most crocodiles and alligators have, and in consequence cannot prey on large creatures, the reduced weight and water resistance of their lighter skull and very narrow jaw gives gharials the ability to catch rapidly moving fish, using a side-to-side snapping motion.
The earliest gharial may have been related to the modern types: some died out at the same time as the dinosaurs (at the end of the Cretaceous), others survived until the early Eocene. The modern forms appeared at much the same time, evolving in the estuaries and coastal waters of Africa, but crossing the Atlantic to reach South America as well. At their peak, the Gavialoidea were numerous and diverse; they occupied much of Asia and America up until the Pliocene. One species, Rhamphosuchus crassidens of India, is believed to have grown to an enormous 15 metres (~50 feet) or more.
Taxonomy
The gharial and its extinct relatives are grouped together by taxonomists in several different ways:
- If the three surviving groups of crocodilians are regarded as separate families, then the gharial becomes one of two members of the Gavialidae, which is related to the families Crocodylidae (crocodiles) and Alligatoridae (alligators and caymans).
- Alternatively, the three groups are all classed together as the family Crocodylidae, but belong to the subfamilies Gavialinae, Crocodylinae, and Alligatorinae.
- Finally, palaentologists tend to speak of the broad lineage of gharial-like creatures over time using the term Gavialoidea.
Classification
- Order Crocodilia
- Superfamily Gavialoidea
- Genus †Eothoracosaurus
- Genus †Thoracosaurus
- Genus †Eosuchus
- Genus †Argochampsa
- Family Gavialidae
- Subfamily Gavialinae
- Genus Gavialis
- Gavialis gangeticus – modern gharial
- †Gavialis curvirostris
- †Gavialis breviceps
- †Gavialis bengawanicus
- †Gavialis lewisi
- Genus Gavialis
- Subfamily Tomistominae
- Genus Tomistoma
- Tomistoma schlegelii, false gharial or Malayan gharial
- †Tomistoma lusitanica
- †Tomistoma cairense
- Genus †Eogavialis
- †Eogavialis africanus
- †Eogavialis andrewsi
- Genus †Kentisuchus
- Genus †Gavialosuchus
- Genus †Paratomistoma
- Genus †Thecachampsa
- Genus †Rhamphosuchus
- Genus †Toyotamaphimeia
- Genus Tomistoma
- Subfamily †Gryposuchinae
- Genus †Aktiogavialis
- Genus †Gryposuchus
- Genus †Ikanogavialis
- Genus †Siquisiquesuchus
- Genus †Piscogavialis
- Genus †Hesperogavialis
- Subfamily Gavialinae
- Superfamily Gavialoidea
Vernacular names
Common names include Indian gharial, Indian gavial, Fish-eating crocodile, Gavial del Ganges, Gavial du Gange, Long-nosed crocodile, Bahsoolia, Chimpta, Lamthora, Mecho Kumhir, Naka, Nakar, Shormon, Thantia, Thondre, Garial.
Appearances in popular culture
- In the PlayStation 2 video game, Metal Gear Solid 3: Snake Eater, one of the more noted animals that Naked Snake can consume for his survival is the Indian Gharial.
- The Ravnica: City of Guilds expansion of the Magic: The Gathering trading card game features a "Crocodile" creature called Grayscaled Gharial, and the Shards of Alara expansion includes the creature Algae Gharial.
- In Esperanto, the verb gaviali ("to gharial") means to speak Esperanto in a situation where another language would be more appropriate.
0 comments :
Post a Comment