Indian gharial - Gavialis gangeticus Feb 13, 2017 6:56:50 GMT 5
Post by Ceratodromeus on Feb 13, 2017 6:56:50 GMT 5
Geographic distribution & Habitat use
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, and Son River Sanctuary. Another small population exists in the rainforest biome of Mahanadi in Satkosia Gorge Sanctuary, Odisha, 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.
They are sympatric with the mugger crocodile (Crocodylus palustris) and formerly with the saltwater crocodile (Crocodylus porosus) in the delta of Irrawaddy River.
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 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.
Like other crocodilians, gharials are ectothermic (cold-blooded), and use sun basking to warm up and water to cool down.Despite the limited ability of terrestrial locomotion in the gharial, they bask on exposed sand banks (rarely on rocks) daily, except sometimes when there is rain. In parts of its range this species basks more than the mugger crocodile. Although gharials often bask in groups, each individual may have a preferred spot that it defends.During the cold season where the air temperature typically is about 18 °C (64 °F) and the water about 17 °C (63 °F) basking occurs throughout the day. During the warm season where the air temperature typically is about 35 °C (95 °F) and the water about 25 °C (77 °F) gharials bask less and avoid midday basking.
The gharial is characterized by its extremely long, thin jaws, which are regarded as an adaptation to a primarily piscivorous diet. Males reach up to 6 m (20 ft) with an average weight of around 160 kg (350 lb).
It is dark or light olive above with dark cross-bands and speckling on the head, body and tail. Dorsal surfaces become dark, almost grey-black, at about 20 years of age. Ventral surfaces are yellowish-white. The neck is elongated and thick. The dorsal ridges are more or less restricted to the median regions of the back. The fingers are extremely short and thickly webbed. Males develop a hollow bulbous nasal protuberance at the tip of the snout upon sexual maturity. The name gharial is derived from the resemblance of the nasal growth to an earthen pot known locally as 'ghara'. Gharials are the only extant crocodilian with visible sexual dimorphism. Although the function of the nasal boss is not well understood, it is apparently used as a visual sex indicator, as a sound resonator, or for bubbling or other associated sexual behaviours.
The average size of mature gharials is 3.5 to 4.5 m (11 to 15 ft). The largest recorded length is 6.25 m (20.5 ft), and the largest recorded weight is 977 kg (2,154 lb). Hatchlings approximate 37 cm (15 in).Young gharials can reach a length of 1 m (3.3 ft) in 18 months. The average body weight ranges from 159 to 250 kg (351 to 551 lb). Males commonly attain a total length of 3 to 5 m (9.8 to 16.4 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 elongated, narrow snout is lined by 110 sharp interdigitated teeth and becomes proportionally shorter and thicker as an animal ages. There are 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 supratemporal fossae. The lower anterior margin of the orbit (jugal) is raised and its mandibular symphysis is extremely long, extending to the 23rd or 24th tooth. A dorsal plate 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. The nuchal and dorsal scutes form a single continuous plate 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 crest on the outer edge of the forearm, leg, and foot. Typically, adult gharials have a dark olive colour tone, while the young are pale olive, with dark brown spots or cross-bands.
The well-developed, laterally flattened tail and webbed rear feet provide tremendous manoeuvrability in deepwater habitat. On land, however, an adult gharial can only push itself forward and slide on its belly. The laterally compressed tail serves both to propel the animal and as a base from which to strike at prey.
The three largest specimens reported were a 6.5-m gharial killed in the Gogra River of Faizabad in August 1920, a 6.3-m individual shot in the Cheko River of Jalpaiguri in 1934, and a giant of 7-m animal, which was shot in the Kosi River of northern Bihar in January 1924. Though specimens of over 6 m (20 ft) were not uncommon in the past, such large individuals are not known to exist today.
Their elongated, narrow snout reduces resistance to water when hunting fish, while the very sharp interdigitated teeth are well adapted for capturing them. Young gharials eat insects, tadpoles, small fish and frogs. Adults feed on fish and small crustaceans. Their jaws are too thin and delicate to grab larger prey, especially people. They catch fish by lying in wait for fish to swim by, and then catch the fish by quickly whipping their heads sideways and grabbing it in their jaws. They herd fish with their bodies against the shore, and stun fish using their underwater jaw clap. They do not chew their prey, but swallow it whole. Young gharials forage and hide in shallow water. With body size increasing, they forage in deeper water. Gharials up to 120 cm (47 in) prefer 1–3 m (3.3–9.8 ft) deep water, those up to 180 cm (71 in) hunt and hide in 2–3 m (6.6–9.8 ft) deep water. Adult gharials prefer water deeper than 4 m (13 ft) for foraging and hiding.
Gharials do not kill and eat humans. Jewelry found in their stomachs may have been the reason for the myth that gharials are man-eaters. They may have swallowed this jewellery as gastroliths used to aid digestion or buoyancy management.
Males mature at around 13 years old, which is when the ghara begins to grow on the snout. They advertise for mates by making hissing and buzzing noises as they patrol their territories, and may have a harem of females within a territory which they aggressively defend from other males. Females communicate their readiness to mate by raising their snouts upwards. During courtship, males and females follow prospective mates around until a suitable mate is chosen. Courtship also involves head and snout rubbing and mounting by both males and females.
Gharials usually mate during December and January. During the dry season in March and April, they dig nests in a riverside sand or silt bank, 1–5 m (3.3–16.4 ft) away from the waterline. Using their hind feet, they dig 50–60 cm (20–24 in) deep holes, in which the female lays 20–95 eggs.The eggs are the largest of any crocodilian species and weigh an average of 160 g. After 71 to 93 days of incubation, young gharials hatch in July just before the onset of the rainy season. Their sex is most likely determined by temperature, like in other crocodilians too. Female gharials dig up the young in response to hatching chirps, but do not assist the hatchlings to reach the water. They guard the hatchlings for some time.