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Tomistoma schlegeliiFalse gharial, Sunda Gavial

By Katie Foster

Geographic Range

False gharials are freshwater crocodiles that are found throughout Indonesia (including Kalimantan, eastern Sumatra, western Java, and western Borneo), parts of Malaysia (including Peninsular Malaysia and Sarawak), and Brunei. There have been unconfirmed reports of false gharials in Vietnam and Sulawesi, Indonesia. They are assumed to be extirpated in southern Thailand, where they have not been seen since the 1970s. False gharial populations are isolated and occur in low densities throughout their range. The largest known populations are in Sumatra and Kalimantan, with smaller established populations in Malaysia. The highest density population of false gharials is in Tanjung Puting National Park in Kalimantan. (Bezuijen, et al., 2010; Crocodile Specialist Group, 2000; Mathew, et al., 2011; Pfaff, 2004; Staniewicz, 2011; Stuebing, et al., 2004; Stuebing, et al., 2006)

Habitat

False gharials are found in a variety of habitats throughout their range, including lowland freshwater swamp forests, flooded forests, peat swamps, lakes, and blackwater streams and rivers. They are also found on the fringes of rainforests near slow-moving rivers. Their preferred habitats are peat swamp areas with low elevation and acidic, slow-moving muddy water; they are also found in secondary forest habitat, characterized by more defined river channels and banks, higher pH and elevation, and a lack of peat mounds. This species needs terrestrial areas for basking and nesting. (Bezuijen, et al., 2010; Crocodile Specialist Group, 2000; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011; Stuebing, et al., 2004; Stuebing, et al., 2006)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools
  • Range elevation
    0 to 20 m
    0.00 to 65.62 ft
  • Range depth
    0.30 to 1.10 m
    0.98 to 3.61 ft

Physical Description

False gharials are large crocodilians characterized by a long, narrow snout snout filled with 76-84 sharp pointed teeth, similar to that of gharials (Gavialis gangeticus), from which false gharials get their common name. False gharials have a streamlined body and muscular tail, eyes and nostrils on top of the head, and a palatal valve that prevents water from entering the throat while underwater. They are known to grow to 4-5 m in length and may grow even larger. There are records of captive adults weighing from 93-201 kg. Both adults and juveniles have dark, sometimes chocolate brown coloration, with black banding on the tail and body and dark patches on the jaws. The belly is cream-colored or white. Males are longer and heavier than females. (Bezuijen, et al., 2010; Britton, 2012a; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011)

  • Sexual Dimorphism
  • male larger
  • Range mass
    93 to 210 kg
    204.85 to 462.56 lb
  • Range length
    4 to 5 m
    13.12 to 16.40 ft

Development

False gharial eggs have a soft inner membrane and harder, calcified shell. Crocodilian sex is determined by temperature rather than genetics. Incubation lasts approximately 90 days and young resemble small adults upon hatching. Hatchlings are equipped with an “egg tooth”, a pointed structure on the end of the snout that allows the hatchling to slice through the egg shell; this recedes a few weeks after hatching. (Britton, 2012a; Staniewicz, 2011)

Reproduction

Very little is known about the natural mating behaviors of false gharials; most details are from captive breeding programs, with a few acocunts from the wild. Courtship behavior and nesting appear to take place during the rainy season in both cases. Males approach females in the water, swimming around them. In some cases, this is accompanied by both animals hitting each other with their tails, in others copulation proceeds immediately. The male mounts the female, wrapping his tail around and under hers. Copulation occurrs once a day for several days to a week, and is accompanied by a strong odor. One captive breeding program in Malaysia had success housing a group of 3 males and 1 female. The female chose the largest male and appeared to stay near him during the courting period. When 2 females were kept in the same enclosure with the males, no mating occurred and it is theorized that females living in close proximity may suppress breeding in one another. (Bezuijen, et al., 1997; Mathew, et al., 2011)

False gharials are mound-nesting crocodilians that lay very large eggs (records up to 9.5 cm long and 6.2 cm wide), with a total mass approximately double that of any other species (eggs may weigh up to 155 gm each). Mounds are usually constructed on land at the shady base of a tree near water, using sand and vegetation including peat, twigs, tree seeds, and dried leaves. Females have been observed beginning nest building a month or more after copulation and laying a clutch of 20-60 eggs 1-2 weeks after beginning to nest. After eggs are laid, more vegetation is added to the top of the nest by the female. Mounds typically measure 45-60 cm high and 90-110 cm in diameter. Eggs are laid just above ground level and the temperature within the nest fluctuates depending on the environment and rainfall (records in captivity of 26°C-32°C). Eggs hatch after 90-100 days. Captive breeding initiatives have shown that abundant vegetation improves the chances of breeding because it provides more cover and nesting material for the female. Both sexes reach sexual maturity at around 20 years of age (females measuring 2.5-3 m in length). (Bezuijen, et al., 2010; Britton, 2012a; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011)

  • Breeding interval
    False gharials breed twice yearly.
  • Breeding season
    False gharial breeding occurs during the wet seasons: November-February and April-June.
  • Range number of offspring
    20 to 60
  • Range gestation period
    90 to 115 days
  • Average age at sexual or reproductive maturity (female)
    20 years
  • Average age at sexual or reproductive maturity (male)
    20 years

Males exhibit no parental investment beyond fertilization. Females have occasionally been observed sitting on top of nest mounds or defending them by stomping the ground, but more often flee the nest if approached. There is evidence that females may help to excavate nests before or during hatching. but they have not been observed helping hatchlings to the water as some crocodilians do. No parental investment beyond this has been observed. (Bezuijen, et al., 1997; Britton, 2012a; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • protecting
      • female

Lifespan/Longevity

False gharials are long-lived animals with an estimated lifespan in the wild of 60 to 80 years, similar to that of other crocodilians. Reports show that captive specimens have a shorter lifespan. (Britton, 2012a)

  • Typical lifespan
    Status: wild
    60 to 80 years

Behavior

False gharials spend most of their time submerged in shallow wallows or mud-holes, with only their eyes and nostrils visible. Crocodilians are capable of staying underwater for long periods of time. They usually submerge for 10-15 minutes, but can stay submerged for as long as 2 hours to avoid a perceived threat. This is accomplished by slowing down their metabolism and reducing oxygen consumption. Basking behavior is likely used to aid in thermoregulation, though it is not often observed. It has been suggested that these animals may occasionally occupy burrows. (Britton, 2012a; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011; Stuebing, et al., 2004)

Home Range

Home range size and territorial behaviors are not known in the wild. In captivity, multiple males and females can be housed in a single enclosure with no apparent aggression. (Mathew, et al., 2011)

Communication and Perception

Communication among false gharials has not been observed in the wild. From observed mating behaviors, it can be assumed that they communicate visually, tactilely and through olfaction. Although most crocodilians use a variety of calls to communicate with their own species and to other animals, these have not been recorded for false gharials and, in fact, their mating has been observed to be silent, rather than accompanied by calls. All crocodilians possess integumentary sense organs located in the skin and covering much of the animal’s body including the body, tail, cloaca and inner surfaces of the legs, as well as on the head and jaws. These are likely used to detect changes in pressure caused by touch or the movement of prey in water; this sense is likely used for hunting in murky water. (Britton, 2012b; Britton, 2012a)

Food Habits

False gharials are opportunistic carnivores. They have been reported to grab monkeys (Crab-eating macaques (Macaca fascicularis) and other Macaca sp.) from river banks, submerging and drowning their prey or beating it against the bank. Other prey items include wild pigs, mouse deer, dogs, otters, fish, birds, turtles, snakes, monitor lizards, and aquatic and terrestrial invertebrates. (Bezuijen, et al., 1997; Britton, 2012a; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011)

  • Animal Foods
  • birds
  • mammals
  • reptiles
  • fish
  • insects
  • terrestrial non-insect arthropods
  • aquatic crustaceans

Predation

Adult false gharials are usually safe from predators due to their large size. Eggs and hatchlings preyed upon by Wild pigs (Sus scrofa) and larger reptiles, such as monitor lizards. Eggs may be collected and consumed by humans as well. In captivity, hatchlings have been killed by termites and ants before emerging from the nest mound. (Bezuijen, et al., 1997; Mathew, et al., 2011; "False Gharial", 2012)

  • Known Predators

Ecosystem Roles

The role of false gharials in their ecosystem is not completely understood due to a lack of study in the wild. They are large predators, preying on a variety of animals and keeping their populations in check. Their distribution overlaps with that of Siamese crocodiles (Crocodylus siamensis) and saltwater crocodiles (Crocodylus porosus), and it is not known how much competition for resources there is amongst these species. (Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011)

Commensal/Parasitic Species
  • Nematodes (Phylum Nematoda)

Economic Importance for Humans: Positive

False gharials were once hunted for their skins, but their skins are not currently considered commercially valuable. In the Mesangat area, their eggs are collected for use in traditional medicine. There is a good deal of research being done to learn more about the roles these animals play in their environments, as well as to determine whether they should be placed in the family Crocodylidae or the family Gavialidae. (Densmore and Owen, 1989; Pfaff, 2004; Staniewicz, 2011)

Economic Importance for Humans: Negative

False gharials are not considered to be a threat to humans. There has been only one documented case of an attack on a human, and one documented attack on a cow in eastern Kalimantan. (Bezuijen, et al., 2010)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

Since the 1890s, sightings and captures of wild specimens have been rare, and it has become increasingly difficult for researchers to locate any individuals for study. Populations, which tend to be very small, are restricted to small patches of swamp or forest. There has been a significant decline in the density of populations since the 1940s. In 2000 this species was assessed by the Crocodile Specialist Group and reported as endangered, with an estimate of less than 2,500 individuals remaining in the wild. More surveys must be conducted to determine the number of individuals remaining before a conservation plan can be developed. The Crocodile Specialist Group Tomistoma Task Force (CSG-TTF) has conducted fundraising for field research and international awareness, and produced reports on conservation priorities and captive breeding. False gharials are threatened by many factors including habitat loss through forest fires, drainage of wetlands, logging, agriculture development, slash and burn agriculture, and dam building. These activities have reduced this species' range in Sumatra by 30-40%. False gharials are now legally protected throughout their entire range, but enforcement of laws has been insufficient to maintain stable populations and breeding habitat. Trade of the species is also prohibited by law, but not well enforced. (Bezuijen, et al., 2010; Britton, 2012a; Crocodile Specialist Group, 2000; Mathew, et al., 2011; Pfaff, 2004; "False Gharial", 2012; Staniewicz, 2011; Stuebing, et al., 2004; Stuebing, et al., 2006)

Other Comments

There is debate over this species’ taxonomic classification. False gharials are currently listed included in the family Crocodylidae based on fossil evidence and morphological similarities to extant crocodiles. Other data, including biochemical, immunological and molecular characters suggest a closer relationship to the family Gavialidae. Studies of nuclear genes suggest the grouping of tomistomine and gavialine crocodilians into one taxon, which would comprise a sister group to the Crocodylidae. Other crocodilian researchers suggest considering Tomistominae and Gavialinae as sister taxa. (Bezuijen, et al., 2010; Britton, 2012a; Crocodile Specialist Group, 2000; Gatesy, et al., 2003; Harshman, et al., 2003; Pfaff, 2004)

Contributors

Katie Foster (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, Jeremy Wright (editor), University of Michigan-Ann Arbor.

Glossary

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Saint Louis Zoo. 2012. "False Gharial" (On-line). Saint Louis Zoo. Accessed September 29, 2012 at http://www.stlzoo.org/animals/abouttheanimals/reptiles/alligatorsandcrocodiles/falsegharial/.

Bezuijen, M., P. Hartoyo, M. Elliott, B. Baker. 1997. Second report on the ecology of the False gharial (Tomistoma schlegelii) in Sumatera. Project Tomistoma: i-38. Accessed February 28, 2013 at http://www.iucncsg.org/365_docs/attachments/protarea/Ecol-acea79fd.pdf.

Bezuijen, M., B. Shwedick, R. Sommerlad, C. Stevenson, R. Steubing. 2010. Tomistoma Tomistoma schlegelii. Pp. 133-138 in S Manolis, C Stevenson, eds. Crocodile: Status Survey and Conservation Action Plan. Darwin: Crocodile Specialist Group.

Britton, A. 2012. "Crocodilians: General Biology" (On-line). Crocodilian Biology Database. Accessed February 28, 2013 at http://crocodilian.com/cnhc/cbd-gb1.htm.

Britton, A. 2012. "Crocodilians: Natural History and Conservation" (On-line). Crocodilians: Natural History and Conservation. Accessed September 29, 2012 at http://crocodilian.com/cnhc/csp_tsch.htm.

Crocodile Specialist Group, 2000. "Tomistoma schlegelii (False gharial, Malayan Gharial, Sunda gharial, Tomistoma, Tomistoma)" (On-line). IUCN Redlist of Threatened Species. Accessed September 29, 2012 at http://www.iucnredlist.org/details/21981/0.

Densmore, L., R. Owen. 1989. Molecular Systematics of the Order Crocodilia. Integrative and Comparative Biology, 29/3: 831-841. Accessed February 28, 2013 at http://icb.oxfordjournals.org/content/29/3/831.abstract.

Gatesy, J., G. Amato, M. Norell, R. DeSalle, C. Hayashi. 2003. Combined Support for Wholesale Taxic Atavism in Gavialine Crocodylians. Systematic Biology, 52: 403-422.

Harshman, J., C. Huddleston, J. Bollback, T. Parsons, M. Braun. 2003. True and False Gharials: A Nuclear Gene Phylogeny of Crocodylia. Systematic Biology, 52: 386-402.

Mathew, A., M. Ganesan, R. Majid, C. Beastall. 2011. "Breeding of False Gharial (Tomistoma schlegelii) at Zoo Negara, Malaysia" (On-line pdf). Zoo Negara. Accessed September 25, 2012 at http://zoonegaramalaysia.my/RPFalseGharial.pdf.

Pfaff, C. 2004. "North American Regional False Gavial Studbook" (On-line pdf). San Diego Zoo. Accessed September 25, 2012 at http://library.sandiegozoo.org/studbooks/reptiles/falsegavial2004.pdf.

Staniewicz, A. 2011. "Diet and demography of Tomistoma schlegelii in Mesangat Lake, East Kalimantan, Indonesia" (On-line pdf). EAZA IUCN/SSC Southeast Asia Campaign. Accessed September 25, 2012 at http://www.southeastasiacampaign.org/download/publications/2011%20Mesangat%20Tomistoma%20report.pdf.

Stuebing, R., S. Sah, E. Lading, J. Jong. 2004. The status of Tomistoma schlegelii (Muellar) in Malaysia. Crocodiles: Proceedings of the 17th Working Meeting of the IUCN-SSC Crocodile Specialist Group, 1: 136-140. Accessed September 25, 2012 at http://eprints.usm.my/9948/1/The_Status_of_Tomistoma_Schlegelii_%28Mueller%29_in_Malaysia.pdf.

Stuebing, R., M. Bezuijen, M. Auliya, H. Voris. 2006. The current and historical distribution of Tomistoma schlegelli (the false gharial). The Raffles Bulletin of Zoology, 54: 181-197. Accessed September 25, 2012 at http://rmbr.nus.edu.sg/rbz/biblio/54/54rbz181-197.pdf.

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