Saltwater crocodile (Crocodylus porosus)

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Immature saltwater crocodile swimming underwater, exhaling
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Saltwater crocodile fact file

Saltwater crocodile description

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderCrocodylia
FamilyCrocodylidae
GenusCrocodylus (1)

The saltwater crocodile (Crocodylus porosus) is the largest of all crocodilians, and the largest reptile in the world, with unconfirmed reports of individuals up to an impressive eight to ten metres in length, although a maximum of five to six metres is more usual (2) (3) (5). The species has a relatively large head, with a pair of ridges that run from the eye along the centre of the snout. Adults are generally dark in colour, with lighter tan or grey areas, and dark bands and stripes on the lower flanks. The underside is creamy yellow to white, becoming greyer along the tail. The juvenile is usually pale tan, with black stripes and spots on the body and tail, which gradually fade with age, although never disappear entirely. Female saltwater crocodiles grow to a smaller size than males, normally reaching a maximum length of 2.5 to 3 metres (3).

With its long, powerful tail, webbed hind feet, and long, powerful jaws, the saltwater crocodile is a superbly adapted aquatic predator. As in all crocodilians, the eyes, ears and nostrils are located on top of the head, allowing the crocodile to remain almost totally submerged when lying in water, helping to conceal it from potential prey, while a special valve at the back of the throat allows the mouth to be opened underwater without water entering the throat (2) (6). The saltwater crocodile is considered to be more aquatic than most crocodilians, and is less heavily armoured along the back and neck (3).

Also known as
Estuarine crocodile, Indo-Pacific crocodile, saltie.
French
Crocodile D'Estuaire, Crocodile Marin.
Spanish
Cocodrilo Poroso.
Size
Length: up to 7 m (2)
Weight
up to at least 1000 kg (3)
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Saltwater crocodile biology

The saltwater crocodile is a powerful and opportunistic predator, feeding on a wide variety of prey. Juveniles take smaller items such as insects, amphibians, crustaceans and fish, while adults also take reptiles, birds and mammals. The largest individuals occasionally take much larger prey such as dingoes, wallabies, domestic animals, and even humans, and will sometimes eat carrion (2) (3) (7) (8) (9). Stones and pebbles may also be ingested, to help grind food in the stomach (8). Where the range of the saltwater crocodile overlaps with that of the Australian freshwater crocodile, Crocodylus johnstoni, the saltwater crocodile outcompetes and sometimes kills the latter (3).

The saltwater crocodile breeds in the wet season, with courtship occurring in northern Australia between September and October, and nesting between November and March. Breeding territories are usually established along tidal rivers or freshwater areas, the female choosing a nesting site near water. The nest itself is a mound, around 175 centimetres long and 53 centimetres high, constructed from vegetation and mud, into which the female lays around 40 to 60, or sometimes up to 90, eggs. The female guards the nest during the 80 to 98 day incubation period, although eggs are sometimes lost to predators, and entire nests are often lost to flooding (2) (3) (5) (8) (10). The hatchlings measure around 29 centimetres (8) and, like all crocodilians, the sex is determined by the incubation temperature, with low temperatures producing mainly females, and higher temperatures mainly males (2) (3) (6) (8).

Crocodilians show a remarkable level of maternal care, the female excavating the nest in response to calls from the hatchlings, and even gently rolling eggs in the mouth to assist hatching. The female will then carry the hatchlings to water, and remain with the young for several months. Despite this level of care, only an estimated one percent of all young reach maturity, being vulnerable to a range of predators and even to cannibalism by adults (2) (3) (6) (8). The young start to disperse at about eight months, and territorial behaviour begins at about 2.5 years (7), although breeding does not usually begin until about 12 to 14 years in females (at a length of around 2.1 to 2.5 metres), and 16 to 17 years (at 3.1 to 3.3 metres) in males (2) (3) (7) (8). Like other crocodilians (6), the saltwater crocodile is potentially long-lived, surviving to over 65, or perhaps even to over 100 years (7) (8).

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Saltwater crocodile range

The saltwater crocodile is the most widely distributed crocodilian species, ranging from Sri Lanka and the east coast of India in the west, through southeast Asia to Australia, and as far east as the Caroline Islands, in the Western Pacific (1) (2) (3) (5) (7). However, it is now thought to be extinct from Singapore and the Seychelles islands, and possibly from Thailand (1) (3). The species is able to travel long distances by sea, sometimes over a thousand kilometres (3), and wandering individuals have been recorded as far as Japan, the Fiji Islands and the Cocos-Keeling Islands (7).

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Saltwater crocodile habitat

As its common name implies, the saltwater crocodile has a high tolerance for saltwater, aided by salt-excreting glands on the tongue (6). It may be found in brackish water around coastal areas and rivers, often amongst mangrove forest, as well as occurring further out to sea, and also occurs in freshwater rivers, lakes, swamps and marshes, up to 200 kilometres inland (1) (2) (3) (7) (8). Individuals move between different habitats between the wet and dry seasons, and dominant breeding adults typically force younger crocodiles out of freshwater areas and into more marginal and saline habitats. The least dominant individuals may be forced out to sea, moving along the coast in search of other river systems (3) (5) (6).

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Saltwater crocodile status

The saltwater crocodile is classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix I and II of CITES (4).

IUCN Red List species status – Least Concern

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Saltwater crocodile threats

As well as being hunted for its meat and eggs, the saltwater crocodile has the most commercially valuable skin of any crocodilian (2) (3) (5), and unregulated hunting during the 20th Century caused a dramatic decline in the species throughout its range, with the population in northern Australia reduced by around 95 percent by 1971. However, the species has since made a dramatic recovery (3) (5) (6) (7) (8), although illegal hunting still persists in some areas, with protection in some countries ineffective (3) (5), and trade often difficult to monitor and control over such a vast range (5).

Habitat loss is also a major problem (3) (5). In northern Australia, much of the nesting habitat of the saltwater crocodile has been destroyed by the trampling of feral water buffaloes (7), although buffalo eradication programs have now reduced this problem considerably (3). However, even where large areas of suitable habitat remain, subtle habitat alterations can be a problem, such as in the Andaman Islands, where freshwater areas, used for nesting, are being increasingly converted for human agriculture (5). Perhaps one of the greatest challenges to the conservation of the saltwater crocodile is its dangerous reputation (2) (5) (7). Although fatalities are not common, and can often be avoided with increased awareness, negative attitudes towards the species can make conservation measures difficult to implement (3) (8).

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Saltwater crocodile conservation

International trade in the saltwater crocodile is carefully monitored and controlled through its listing under Appendix I and II of the Convention on International Trade in Endangered Species (CITES) (4), and the species is also listed under the Convention on Migratory Species (CMS or Bonn Convention) (11), as well as being legally protected throughout much of its range (5) (7). The saltwater crocodile also occurs in a number of protected areas, such as the Ord River Nature Reserve and Kakadu National Park in Australia, and in various reserves across India and Indonesia (3) (5) (7). Australia has been the focus of the most extensive research on the species, with various breeding and conservation programs underway there (3). In the Northern Territory, up to 240 “problem crocodiles” are taken from Darwin Harbour each year, to improve public safety, and are moved to crocodile farms to be used for breeding (2). Sustainable use programs also operate in parts of Australia and a number of other countries, based on the harvesting of eggs from the wild and the rearing of the hatchlings on crocodile farms, to produce meat and skins. Such programs have been very successful in giving people an incentive to conserve both crocodiles and their habitats (2) (3) (5) (6). In other parts of the species’ range, trade relies on captive breeding programs (2). Restocking programs, in which young crocodiles are returned to the wild, have also met with success, such as in Bhitarkanika National Park in Orissa, India (3) (5).

The conservation of crocodile populations is highly dependent on management practices that allow crocodiles and human to co-exist (5) (6), and public awareness and education are important in this. Although the future of the saltwater crocodile is now much more secure than a few decades ago, it is still likely to be lost from many parts of its range unless effective management and protection are put in place. Although sometimes controversial, sustainable use programs are proving effective for saltwater crocodile conservation (3) (5), and its dramatic recovery from near-extinction demonstrates the ability of these formidable reptiles to survive and thrive when properly managed (6).

View information on this species at the UNEP World Conservation Monitoring Centre.
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Find out more

Find out more about the saltwater crocodile and the conservation of this and other crocodilian species: 

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Brackish
Slightly salty water, usually a mixture of salt and freshwater, such as that found in estuaries.
Carrion
The flesh of a dead animal.
Crocodilian
A member of the order Crocodylia, a group which includes crocodiles, alligators, caimans and gharials.
Crustaceans
Diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
Feral
Previously domesticated animals that have returned to a wild state.
Incubation
The act of incubating eggs; that is, keeping them warm so that development is possible.
Territorial
An animal, a pair of animals or a colony that occupies and defends an area.
Territory
An area occupied and defended by an animal, a pair of animals or a colony.
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References

  1. IUCN Red List (April, 2011)
    http://www.iucnredlist.org
  2. IUCN/SSC Crocodile Specialist Group (September, 2009)
    http://www.iucncsg.org/
  3. Crocodilian Species List: Crocodylus porosus (September, 2009)
    http://www.flmnh.ufl.edu/cnhc/csp_cpor.htm
  4. CITES (September, 2009)
    http://www.cites.org
  5. Ross, R.P. (1998) Crocodiles: Status Survey and Conservation Action Plan. Second Edition. IUCN/SSC Crocodile Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
    http://www.flmnh.ufl.edu/natsci/herpetology/act-plan/plan1998a.htm
  6. Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.
  7. UNEP-WCMC (September, 2009)
    http://www.unep-wcmc.org/species/data/species_sheets/crocodil.htm
  8. Estuarine crocodile, Crocodylus porosus (September, 2009)
    http://www.kingsnake.com/oz/crocs/porosus.htm
  9. Letnic, M. and Connors, G. (2006) Changes in the distribution and abundance of saltwater crocodiles (Crocodylus porosus) in the upstream, freshwater reaches of rivers in the Northern Territory, Australia. Wildlife Research, 33: 529 - 538.
  10. Webb, G.J.W., Messel, H. and Magnusson, W. (1977) The nesting of Crocodylus porosus in Arnhem Land, Northern Australia. Copeia, 2: 238 - 249.
  11. Convention on the Conservation of Migratory Species of Wild Animals (September, 2009)
    http://www.cms.int
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Image credit

Immature saltwater crocodile swimming underwater, exhaling  
Immature saltwater crocodile swimming underwater, exhaling

© Reinhard Dirscherl / Biosphoto

Biosphoto
16 rue Velouterie
Avignon
84000
France
Tel: +33 (490) 162 042
Fax: +33 (663) 208 434
http://www.biosphoto.com/

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