Gavialis gangeticus

Geographic Range

Gavialis gangeticus is found in the northern part of the Indian subcontinent. It historically inhabits four river systems: the Indus (Pakistan), the Ganges (India and Nepal), the Mahanadi (India) and the Brahmaputra (Bangladesh, India, and Bhutan); it also may have occurred in the Ayeyarwaddy River in Burma (Myanmar). It has become extinct in many areas where it formerly occurred.

• Biogeographic Regions
• oriental oriental
  • native native

Habitat

Indian gharials live in clear freshwater rivers with fast flowing currents. They congregate at river bends and other sections of rivers where the water is deep and the current is reduced. Because Indian gharials are not well adapted for movement on land, they usually leave the water only to bask and to nest. They prefer sandbars in the middle of the rivers for both of these activities. Juveniles may seek out quiet backwaters or smaller streams.

• Habitat Regions
• tropical tropical
• freshwater freshwater

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• riparian riparian

Physical Description

Indian gharials are one of the largest crocodilians in the world. Males grow to be between 5 and 6 meters long, with the larger ones approaching 6.5 meters. Females are smaller, but reach more than 4 meters. The snout is long and slender, specialized for catching fish. The snout shape changes throughout the lifetime, usually becoming longer and thinner as individuals get older. There are between 106 and 110 razor sharp teeth in the jaws; 5 pre-maxillary, 23 to 24 maxillary, and 25 to 26 mandibular teeth. Males have a bulbous growth on the end of their snout called a "ghara." It functions during courtship as a visual stimulus for females and it helps to produce bubbles during mating. It also allows gharials to produce a loud buzzing sound. Indian gharials are equipped with extensively webbed feet for locomotion in the water. Movement on land is inefficient. The leg muscles are not strong enough to lift them off the ground, but they can push themselves along while sliding on the belly. The scales of gharials are smooth, which is different from most crocodiles and alligators . Adults are dark brown to greenish brown on top with a yellowish white to white underneath. Young Indian gharials have dark bands on the body and tail that usually fade as they become adults.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes shaped differently
• ornamentation ornamentation

Development

Fertilization is internal. Females lay shelled eggs in nests dug into sandy riverbanks and guard the nests during the more than 60 day incubation period. Sex is determined by egg temperature during the early to middle part of the incubation period.

• Development - Life Cycle
• temperature sex determination

Reproduction

The "gharal" is used in mating. This is a cartilaginous lid on the nostril of males that flaps when exhaling, producing a loud buzzing noise, which is used during territorial defense and courtship. Males also hiss, and perform above water jaw slapping. While underwater, jaw slapping is also performed to attract possible mates. When a female finds a male, they will rub each other with their snouts and the male will follow the female around his territory. The female will then show her readiness to mate by raising her head skyward, at which point the male will climb on top of her. The two will then submerge for up to 30 minutes during copulation.

• Mating System
• polygynous polygynous

Mating season occurs for about two months each year. Mating season varies regionally, but generally occurs between November and February, during the dry season. Nesting occurs during the late dry season, from March through May. Females locate a steep sand bank where they dig a nest. During this time, they might dig a number of holes before finding the right spot. Holes are about 50 cm deep and from 3 to 5 meters from the water. Females lay 28 to 60 eggs in the hole, usually at night. Very large females are capable of laying almost 100 eggs. An average Indian gharial egg is 5.5 centimeters wide, 8.6 centimeters long, and weighs 100 to 156 grams. An incubation period of 60 to 80 days will follow. Females continue to visit and guard eggs during the night but remain in the water during the day. During incubation females are very territorial near the nest, but they tolerate other females nesting on the same beach. Nests in warmer climates usually hatch earlier. Young are about 18 cm in length. The female (and perhaps the male) will help excavate the nest during hatching, but they are probably incapable of picking up the young. Sexual maturity for females is reached at 8 years old and 3 meters in length. For males, maturity is attained at 15 years of age and 4 meters in length. At this time males grow a ghara on their snout.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Females must provision eggs with yolk prior to oviposition, excavate a nest cavity, and guard nests. Females may uncover and assist young during the hatching process. After hatching, females protect hatchlings for several weeks, often until monsoon rains come, during which high water levels may disperse the young. The male will be tolerated nearby, but they do not actively protect hatchlings, though young will sometimes rest on the back of the male.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • protecting
    • female
• pre-independence
  • protecting
    • female

Lifespan/Longevity

The only record of longevity in Gavialis gangeticus is of a captive individual at the London Zoo, where one was estimated at 29 years old. Because of their large size, it is thought that they have a long life span. Fisherman that live near gharials believe that they can live as long as 100 years old, though this has not been confirmed.

Behavior

Indian gharials spend a lot of time basking in the sun, more so in the winter than in the summer. They tend to revisit the same basking spot, which is always close to the water. Indian gharials also "gape" during basking to dissipate excess heat. Gaping is usually done in 10 to 20 minute intervals with the head at a 20 degree angle. On very hot days gharials completely submerge their bodies, leaving only their heads out of the water at a 20 to 30 degree angle. Indian gharials aggreggate in basking and nesting areas but are generally solitary. Nests are defended by females.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial

Home Range

Home range sizes in Indian gharials are not reported.

Communication and Perception

Like all crocodilians , Indian gharials possess integumentary sense organs. These are tiny pits in the scales that cover the body. These pits are able to pick up vibrations or changes in water pressure, which aid in the search for prey. Their eyes have a reflective layer behind the eye, the tapetum lucidum, which aids in night vision. A clear membrane, the nictitating membrane, protects the eye while under water. Indian gharials pick up low frequencies through hearing and are able to close the ear canal when submerged. Indian gharials apparently communicate via vibrations in the water and buzzing sounds made by males with the ghara on their snouts.

• Communication Channels
• visual visual
• acoustic acoustic

• Other Communication Modes
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations

Food Habits

The diet of juvenile gharials is different from adults. Juveniles eat small animals, such as insects, crustaceans, or frogs. But as they grow older and their snout becomes thinner and longer, they eat almost exclusively fish. Their jaws are well adapted for catching fish. There are three main hunting strategies. The sit and wait approach is where they float almost completely submerged under water and remain motionless until their pray passes right by them. The sweeping search involves an integumentary sensory organ found on the scales to sense vibrations in the water while slowly feeling through the water for prey. The third hunting strategy is a rapid strike. The thin jaw creates low water resistance for quick snaps underwater.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • insectivore insectivore
  • eats non-insect arthropods

• Animal Foods
• amphibians
• reptiles
• fish
• insects

Predation

Humans are the greatest threat to Gavialis gangeticus . Indian gharials are poached for their skin, meat, male gharas, and eggs. Gharials are also threatened indirectly through habitat destruction, as people modify habitats for agriculture and industry, and by fishing. Indian gharial eggs are eaten by rats ( Rattus ), golden jackals ( Canis aureus ), wild pigs ( Sus ), mongooses ( Herpestes ), and monitor lizards ( Varanus ). Young Indian gharials are eaten by these predators as well as other, larger aquatic and terrestrial predators.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Indian gharials are important predators of fish. Unfortunately the numbers of gharials are now so low that their effects on the ecosystem may not be significant.

Economic Importance for Humans: Positive

Male Indian gharials are sometimes sought after for their ghara, the growth on the end of their snout, because it is believed by some to carry aphrodisiac properties. Eggs are collected for their supposed medicinal properties. However, both of these supposed medicinal properties are not based on research and it is unlikely that the eggs or the ghara benefit people in any way. Indian gharials may benefit local communities by acting as a tourist attraction.

• Positive Impacts
• body parts are source of valuable material
• ecotourism ecotourism

Economic Importance for Humans: Negative

This species is probably harmless to human interests. Indian gharials are sometimes believed to attack and eat humans, but this appears to be an unfounded fear. Indian gharials are generally not aggressive and have narrow jaws and thin teeth that are unsuited to attacking humans or large animals.

Conservation Status

The decline from an estimated 436 adult Indian gharials in 1997 to 182 in 2006 represents a 58% drop across their range. This drastic decline happened in a period of nine years, well within the span of one generation, qualifying Indian gharials as Critically Endangered (IUCN). They were the first crocodilian to be categorized as critically endangered. The biggest threat to them is habitat loss and disturbance caused by people clearing riparian areas for firewood or farmland or mining river banks for sand. Poaching is also a problem. Conservation efforts have increased in recent years and attempts to ensure population increases are in place. Action groups such as the Gharial Multi-Task Force are comprised of regional and international crocodilian specialists that are working to avoid the extinction of this animal in the wild. Information about the current status of Indian gharials in the wild is still being collected. Conservation efforts and management strategies cannot be put into place without good data to back them. Surveys of areas such as Pakistan and Burma are some of the next steps to be taken. Other threats to this species include a lack of proper release sites. Eggs are collected by local people for medicinal purposes and adult males are hunted because it is believed that the ghara on their snout acts as an aphrodisiac. Fishing also causes a problem when they are captured by gill nets and are killed in the process. Fishing also greatly reduces the prey base of these animals. It is thought by some local people that Indian gharials are man-eaters, which results in persecution. This fear stems from the fact that human remains are sometimes found in the bellies of gharials. During a Hindu funeral ritual, cremated remains of a body are placed in rivers. It is a common practice for many crocodilians to ingest rocks to be used as gastroliths: hard objects that aid in digestion and alter their buoyancy. It is thought that some human remains and jewelry is ingested in a similar way. Indian gharial jaws are specialized for eating fish and they are not considered dangerous to people. A recent threat to the species is a widespread mortality due to gout. Since 2007 over 110 gharials have succumbed to gout. This may be caused by the introduction of Tilapia into the Yamuna river. It is believed that these fish carry a toxin that effects gharials, but the composition of the toxin and how it enters the river is still being researched.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Kyle Bouchard (author), Michigan State University, James Harding (editor, instructor), Michigan State University.

References

Atroley, A. 2008. "WWF - Gharial Deaths in National Chambal Sanctuary" (On-line). Accessed December 02, 2008 at http://www.wwfindia.org/about_wwf/what_we_do/freshwater_wetlands/freshwater_species/gharial/index.cfm .

Britton, A. 2006. "Crocodilian Species - Gharial (Gavialis gangeticus)" (On-line). Accessed November 17, 2008 at http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_ggan.htm .

Brochu, 2003. "TAXONOMY & NOMENCLATURE" (On-line). Accessed November 18, 2008 at http://spot.colorado.edu/~humphrey/fact%20sheets/gharial/gharial.htm#threats .

Chaudhari, S. 2008. Gharial reproduction and mortality. Iguana , 15(3): 150-153.

Choudhury, B., L. Singh, R. Rao, D. Basu, R. Sharma, S. Hussain, H. Andrews, N. Whitaker, R. Whitaker, J. Lenin, T. Maskey, A. Cadi, S. Rashid, A. Choudhury, B. Dahal, U. Win Ko Ko, J. Thorbjarnarson, J. Ross. 2007. "IUCN 2008 Red List - Gavialis gangeticus" (On-line). Accessed November 17, 2008 at http://www.iucnredlist.org/details/8966 .

Das, I. 2002. A Photographic Guide to the Snakes and Other Reptiles of India . Sanibel Island, Florida: Ralph Curtis Books.

Net Industries, 2008. "Gharial: Gavialidae - Physical Characteristics, Habitat, Diet, Behavior And Reproduction, Conservation Status - GEOGRAPHIC RANGE, GHARIALS AND PEOPLE" (On-line). Accessed November 18, 2008 at http://animals.jrank.org/pages/3629/Gharial-Gavialidae.html .

Ross, J. 1998. "Crocodiles Status Survey and Conservation Action Plan" (On-line). Accessed November 18, 2008 at http://www.flmnh.ufl.edu/natsci/herpetology/act-plan/ggang.htm .

Ross (Editor), C. 1989. Crocodiles and Alligators . New York: Facts On File, Inc..

Vitt, L., J. Caldwell. 2009. Herpetology (3rd Edition) . Burlington, MA: Academic Press.

Wildscreen, 2008. "Gharial (Gavialis gangeticus)" (On-line). Accessed November 18, 2008 at http://www.arkive.org/gharial/gavialis-gangeticus/info.html .

anon., 2008. "Gharial Conservation Alliance" (On-line). Accessed December 15, 2008 at http://www.gharialconservation.org/toxin-suspected-as-cause-of-gharial-deaths/ .