Saltwater crocodile

Saltwater Crocodile
Conservation status
Least Concern  (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Crocodylia
Family:	Crocodylidae
Subfamily:	Crocodylinae
Genus:	Crocodylus
Species:	C. porosus
Binomial name
Crocodylus porosus (Schneider, 1801)
Range of the saltwater crocodile in black

Saltwater or estuarine crocodile (Crocodylus porosus) is the largest of all living crocodilians and reptiles. It is found in suitable habitats throughout Southeast Asia, Northern Australia, and the surrounding waters. The Alligator Rivers are misnamed after the resemblance of the saltwater crocodile to alligators as compared to freshwater crocodiles, which also inhabit the Northern Territory.

Anatomy and morphology

File:LargeCroc.jpg

Saltwater crocodile outside Cairns, Queensland

The saltwater crocodile has a longer muzzle than the mugger crocodile, and is twice the length of its breadth at the base. The saltwater crocodile has fewer armor plates on its neck than other crocodilians, and its broad body contrasts with that of most other lean crocodiles, leading to early unverified assumptions that the reptile was an alligator.

An adult male saltwater crocodile's weight is 880 to 3,000 pounds (400–1,360 kg) and length is normally 4 to 5.1 metres (13–17 ft), though very old males can be 6 metres (20 ft) or more . This species has the greatest sexual dimorphism of any modern crocodilian, with females being much smaller than males. Typical female body lengths in the range of 2.1 to 3.5 metres (6.9–11.5 ft). The largest female on record measured about 4.2 metres (14 ft). The mean weight of the species as a whole is roughly 450 kilograms (990 lb).

The largest size saltwater crocodiles can reach is the subject of considerable controversy. The longest crocodile ever measured snout-to-tail and verified was the skin of a deceased crocodile, which was 6.2 metres (20 ft) long. Since skins tend to shrink slightly after removal from the carcass, this crocodile's living length was estimated at 6.3 metres (21 ft) and it probably weighed well over 1,200 kilograms (2,600 lb). Incomplete remains (the skull of a crocodile shot in Orissa) have been claimed to come from a 7.6 metres (25 ft) crocodile, but scholarly examination suggested a length no greater than 7 metres (23 ft). There have been numerous claims of crocodiles in the 9 metres (30 ft) range: the individual shot in the Bay of Bengal in 1840, reported at 10 metres (33 ft); another killed in 1823 at Jala Jala on Luzon reported at 8.2 metres (27 ft); a reported 7.6 metres (25 ft) crocodile killed in the Hooghly River in the Alipore District of Calcutta. However, examinations of these animals' skulls actually indicated animals ranging from 6 to 6.6 metres (20–22 ft).

With recent restoration in saltwater crocodile habitat and reduced poaching, it is possible that 7 metres (23 ft) or larger crocodiles are alive today. Guinness has accepted a claim of a 7.5 metres (25 ft) male saltwater crocodile, with an estimated weigh of 2,000 kg (4,400 lbs), living within Bhitarkanika Park in the state of Orissa, India, although, due the near impossible task of trapping and weighing a very large, live crocodile, the accuracy of these dimensions have yet to be verified.

A crocodile shot in Queensland in 1957 was reported to be 8.5 metres (28 ft) long, but no verified measurements were made and no remains of this crocodile exist. A "replica" of this crocodile has been made as a tourist attraction. Many other unconfirmed reports of 8+ metres (26+ ft) crocodiles have been made but these are highly suspect.

Distribution

Saltwater crocodiles are severely depleted in numbers throughout much of their range, and are virtually extinct in Thailand (a few individuals may persist in isolated national parks) and Vietnam (with the exception of occasional vagrants from Cambodia). In Cambodia they may possibly exist in very small numbers within the countries rivers and mangroves, although this has not been officially confirmed. The status of this species is unknown within Myanmar (although given the recent fatal attack on a convict, they are definitely present within the Irrawaddy River) and they are known to exist in Bangladesh solely within the Sundarbans. Although Saltwater Crocodiles were once very common in the Mekong Delta (from which they disappeared in the 1980s) and other river systems, the future of this species in Southeast Asia is now looking grim, given that population numbers are either critically low or completely extirpated from almost all regions within Indochina. However, it is also the least likely of crocodilians to become globally extinct due to its wide distribution and almost pre-colonial population sizes in Northern Australia and New Guinea. In India this crocodile is extremely rare in most areas but is very common in the north eastern part of the country (mainly Orissa and the Sunderbans). The population is sporadic in Indonesia and Malaysia with some areas harboring large populations (Borneo, for example) and others with very small, "at risk" populations (e.g., the Philippines). The saltwater crocodile is also present in very limited parts of the South Pacific, with an average population in the Solomon Islands, a very small, invasive and soon to be extinct population in Vanuatu (where the population officially stands at only three) and a decent but at-risk population (which may be rebounding) in Palau. In northern Australia (which includes the top ends of the Northern Territory, Western Australia and Queensland) the Saltwater Crocodile is thriving, particularly in the multiple river systems near Darwin (such as the Adelaide, Mary and Daly Rivers, along with their adjacent billabongs and estuaries) where exceptionally large (6 meter +) individuals are not uncommon. A rough estimate states that the Australian Saltwater Crocodile population stands somewhere between 100,000 and 200,000 adults. Their range extends from Broome in Western Australia through the entire Northern Territory coast all the way down to Rockhampton in Queensland. In New Guinea they are also very common, existing within the coastal reaches of virtually every river system in the country, along with all estuaries and mangroves.

Saltwater crocodiles once ranged as far west as the east coast of Africa at the Seychelles Islands. These crocodiles were once believed to be a population of Nile crocodiles, but they were later proven to be Crocodylus porosus.

Due to this species' tendency to travel very long distances at sea, individual saltwater crocodiles occasionally show up in odd locales where they are not native. Vagrant individuals have historically been reported on New Caledonia, Iwo Jima, Fiji, and even in the relatively frigid Sea of Japan (thousands of miles from their native territory.)

Habitat

Saltwater crocodile sunning itself at Corroboree in the Northern Territory of Australia.

Saltwater crocodiles generally spend the tropical wet season in freshwater swamps and rivers, moving downstream to estuaries in the dry season, and sometimes traveling far out to sea. Crocodiles compete fiercely with each other for territory, with dominant males in particular occupying the most eligible stretches of freshwater creeks and streams. Junior crocodiles are thus forced into the more marginal river systems and sometimes into the ocean. This explains the large distribution of the animal (ranging from the east coast of India to northern Australia) as well as its being found in odd places on occasion (such as the Sea of Japan). Saltwater crocodiles can swim 15 to 18 miles per hour in short bursts, but when cruising go 2 to 3 mph.

Diet and behavior

Saltwater crocodile jumping up in Kakadu National Park

The saltwater crocodile is an opportunistic apex predator capable of taking any animal that enters their territory, either in the water or on dry land. They have also been known to attack humans. Juveniles are restricted to smaller animals such as insects, amphibians, crustaceans, small reptiles and fish. The larger the animal grows, the greater the variety of animals it includes in the diet, although relatively small prey make up an important part of the diet even in adults. Large adult saltwater crocodiles can potentially eat any animal within its range, including monkeys, kangaroos, wild boar, dingos, goannas, birds, domestic livestock, pets, water buffalo, gaurs, sharks, and humans, among other large animals as well. Domestic cattle, horse, water buffalo and gaur, all of which may weigh over a ton, are considered the largest prey taken by male crocodiles. The only threats to adult saltwater crocodiles are other crocodiles and humans. Generally very lethargic – a trait which helps it survive months at a time without food – it typically loiters in the water or basks in the sun through much of the day, preferring to hunt at night. Capable of explosive bursts of speed when launching an attack from the water, many species of crocodile are also capable of fast land-movement. Many crocodiles are capable of explosive charges that can carry them nearly as fast as a running human. The 23 species of crocodilian can travel over land using the belly crawl, the walk, the high-walk, and the gallop. However, stories of crocodiles being faster than a race horse for short distances across the ground are little more than urban legend.

As an ambush predator, it usually waits for its prey to get close to the water's edge before striking, using its great strength to drag the animal back into the water. Most prey animals are killed by the great jaw pressure of the crocodile, although some animals may be incidentally drowned. It is an immensely powerful animal, having the strength to drag a fully grown water buffalo into a river, or crush a full-grown bovid's skull between its jaws.

In its deadliest attack, called the "death roll," it grabs onto the animal and rolls powerfully. This throws any struggling large animal off balance making it easier to drag it into the water. The "death roll" is also used for tearing apart large animals once they are dead.

Attacks on humans

No Swimming sign from the Kakadu National Park.

Saltwater crocodiles are very dangerous animals, but data on attacks is limited outside of Australia, and estimates of human fatalities vary wildly between dozens to thousands annually. It is likely that, given this species' low population within most of its non-Australian/New Guinean range, the number of attacks is probably within the lower range of estimates. Most attacks by adult "salties" are fatal, given the animals' size and strength. In Australia, attacks are rare and usually make headlines when they do occur. There are, on average, no more than one or two fatal attacks reported per year in the country. The low level of attacks is most likely due to the extensive effort by local wildlife officials to post crocodile "warning" signs at nearly every billabong, river, lake and even at some beaches and also due to the relatively well-informed nature of the local citizens. In the Aboriginal community of Arnhem Land, which occupies roughly half of the top end of the Northern Territory, attacks may go unreported and may be more common. The majority of "unreported" attacks most likely occur in New Guinea, where the species population is very high and precautions are few. There have also been recent, less public attacks in Borneo, Sumatra, eastern India and in Myanmar.

Intelligence

Head of a Crocodylus porosus

Dr. Adam Britton, a researcher with Big Gecko, has been studying crocodilian intelligence. In so doing, he has compiled a collection of Australian saltwater crocodile calls, and associated them with behaviors. His position is that while crocodilian brains are much smaller than those of mammals (as low as 0.05% of body weight in the saltwater crocodile), they are capable of learning difficult tasks with very little conditioning. He also infers that the crocodile calls hint at a deeper language ability than currently accepted. He suggests that saltwater crocodiles are clever animals that can possibly learn faster than lab rats. They have also learned to track the migratory route of their prey as the climate changes.

Bibliography

• Template:IUCN2006

References

Marshall, Ben "The Crocodile" New York Publishers Inc. 1999

See also

• Crocodile attack

External links

• Recent Crocodile Attacks in Australia
• Australian Saltwater Crocodile Photos and attack file
• Saltwater crocodile calls from Dr. Britton's crocodilian.com site
• Brief discussion from Dr. Britton and others discussing dromaeosaurid intelligence