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Saltwater crocodile

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Saltwater crocodile
Temporal range: 4.5–0 Ma
↓
Early Pliocene – Recent
Saltwater crocodile at the St. Augustine Alligator Farm Zoological Park, Florida
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
Order: Crocodilia
Family: Crocodylidae
Genus: Crocodylus
Species:
C. porosus
Binomial name
Crocodylus porosus
Schneider, 1801
Range of the saltwater crocodile in black

The saltwater crocodile (Crocodylus porosus) is a crocodilian native to saltwater habitats and brackish wetlands from India's east coast across Southeast Asia and the Sundaic region to northern Australia and Micronesia. It has been listed as Least Concern on the IUCN Red List since 1996.[1] It was hunted for its skin throughout its range up to the 1970s, and is threatened by illegal killing and habitat loss. It is regarded as dangerous for people who share the same environment.[2]

The saltwater crocodile is the largest living reptile and crocodilian known to science.[3][4][5] Males grow to a length of up to 6 m (20 ft), rarely exceeding 6.3 m (21 ft) or a weight of 1,000–1,300 kg (2,200–2,900 lb).[6][7][8] Females are much smaller and rarely surpass 3 m (10 ft).[9][10] It is also known as the estuarine crocodile, Indo-Pacific crocodile, marine crocodile, sea crocodile or informally as saltie.[11]

The saltwater crocodile is a large and opportunistic hypercarnivorous apex predator. It ambushes most of its prey and then drowns or swallows it whole. It is capable of prevailing over almost any animal that enters its territory, including other apex predators such as sharks, varieties of freshwater and saltwater fish including pelagic species, invertebrates such as crustaceans, various reptiles, birds and mammals, including humans.[12][13]

Taxonomy and evolution

Sweetheart, a saltwater crocodile from Finnis River in northern Australia proposed as Crocodilus pethericki in 1985

Crocodilus porosus was the scientific name proposed by Johann Gottlob Theaenus Schneider who described a zoological specimen in 1801.[14] In the 19th and 20th centuries, several saltwater crocodile specimens were described with the following names:

  • Crocodilus biporcatus proposed by Georges Cuvier in 1807 were 23 saltwater crocodile specimens from India, Java and Timor.[15]
  • Crocodilus biporcatus raninus proposed by Salomon Müller and Hermann Schlegel in 1844 was a crocodile from Borneo.[16]
  • Crocodylus porosus australis proposed by Paulus Edward Pieris Deraniyagala in 1953 was a specimen from Australia.[17]
  • Crocodylus pethericki proposed by Richard Wells and C. Ross Wellington in 1985 was a large-bodied, relatively large-headed and short-tailed crocodile specimen collected in 1979 in the Finnis River, Northern Territory.[18] This purported species was later considered to be a misinterpretation of the physiological changes that very large male crocodiles undergo. However, Wells and Wellington's assertion that the Australian saltwater crocodiles may be distinctive enough from northern Asian saltwater crocodiles to warrant subspecies status, as could raninus from other Asian saltwater crocodiles, has been considered to possibly bear validity.[19][20]

Currently, the saltwater crocodile is considered a monotypic species.[21] However, based largely on morphological variability, it is thought possible that the taxon C. porosus comprises a species complex. Borneo crocodile C. raninus specimens can reliably be distinguished both from saltwater and Siamese crocodiles (C. siamensis) on the basis of the number ventral scales and on the presence of four postoccipital scutes, which are often absent in true saltwater crocodiles.[22][23]

Evolution

Fossil remains of a saltwater crocodile excavated in northern Queensland were dated to the Pliocene.[24][25] The oldest known Crocodylus fossils were dated to the Late Miocene. The saltwater crocodile is a sister taxon of the Nile crocodile[26][27] and the Siamese crocodile.[28][29]

Results of phylogenetic research indicate that Crocodylus evolved in the Oligocene Indo-Pacific about 25.5–19.3 million years ago. The warm and wet climate in the tropics during this period may have facilitated the dispersal of crocodiles from Australasia to Africa without having to move long distances at sea. The genetic lineage comprising saltwater, Nile and Siamese crocodiles is estimated to have diverged 10.60–6.52 million years ago. Nile and Siamese crocodiles probably diverged from this group 7.94–4.19 million years ago.[30]

Description

Saltwater crocodile skull from The Museum of Zoology, Russia. Note the considerably more slender skull of a gharial in the background.
Head of a saltwater crocodile

The saltwater crocodile has a wide snout compared to most crocodiles. However, it has a longer snout than the mugger crocodile (C. palustris); its length is twice its width at the base.[31] A pair of ridges runs from the eyes along the centre of the snout. The scales are oval in shape and the scutes are either small compared to other species or commonly are entirely absent. In addition, an obvious gap is also present between the cervical and dorsal shields, and small, triangular scutes are present between the posterior edges of the large, transversely arranged scutes in the dorsal shield. The relative lack of scutes is considered an asset useful to distinguish saltwater crocodiles in captivity or in illicit leather trading, as well as in the few areas in the field where sub-adult or younger saltwater crocodiles may need to be distinguished from other crocodiles. It has fewer armour plates on its neck than other crocodilians.[32][33]

The adult saltwater crocodile's broad body contrasts with that of most other lean crocodiles, leading to early unverified assumptions the reptile was an alligator.[34]

Young saltwater crocodiles are pale yellow in colour with black stripes and spots on their bodies and tails. This colouration lasts for several years until the crocodiles mature into adults. The colour as an adult is much darker greenish-drab, with a few lighter tan or grey areas sometimes apparent. Several colour variations are known and some adults may retain fairly pale skin, whereas others may be so dark as to appear blackish. The ventral surface is white or yellow in colour in saltwater crocodiles of all ages. Stripes are present on the lower sides of their bodies, but do not extend onto their bellies. Their tails are grey with dark bands.[35][36]

Size

The weight of a crocodile increases approximately cubically as length increases (see square-cube law).[37] This explains why individuals at 6 m (20 ft) weigh more than twice that of individuals at 5 m (16 ft).[34] In crocodiles, linear growth eventually decreases and they start getting bulkier at a certain point.[38]

Saltwater crocodiles are the largest extant riparian predators in the world. However, they start life fairly small. Newly hatched saltwater crocodiles measure about 28 cm (11 in) long and weigh an average of 71 g (2+1⁄2 oz).[39] These sizes and ages are almost identical to those at average sexual maturity in Nile crocodiles, despite that average adult male saltwater crocodiles are considerably larger than average adult male Nile crocodiles.[40][41]

The largest skull of a saltwater crocodile that could be scientifically verified was of a specimen in the Muséum national d'Histoire naturelle collected in Cambodia. Its skull was 76 cm (30 in) long and 48 cm (19 in) wide near its base, with 98.3 cm (38+3⁄4 in) long mandibles. The length of this specimen is not known but based on skull-to-total-length ratios for very large saltwater crocodiles its length was presumably somewhere in the 7 m (23 ft) range.[9][42] If detached from the body, the head of a very large male crocodile can reportedly weigh over 200 kg (440 lb) alone, including the large muscles and tendons at the base of the skull that lend the crocodile its massive biting strength.[43] The largest tooth measured 9 cm (3+1⁄2 in) in length.[44][45] Other crocodilians have a proportionately longer skull, like the gharial (Gavialis gangeticus) and the false gharial (Tomistoma schlegelii), both their skulls and bodies are less massive than in the saltwater crocodile.[9]

Male size: An adult male saltwater crocodile, from young adults to older individuals, typically ranges 3.5 to 6 m (11 ft 6 in to 19 ft 8 in) in length and weighs 200 to 1,000 kg (440 to 2,200 lb).[46][47][48] On average, adult males range 4.3 to 4.9 m (14 ft 1 in to 16 ft 1 in) in length and weigh 408 to 522 kg (899 to 1,151 lb).[43] However average size largely depends on the location, habitat, and human interactions, thus changes from one study to another, when figures of each study are viewed separately. In one case, Webb and Manolis (1989) attributed the average weight of adult males in Australian tidal rivers as only 240 to 350 kg (530 to 770 lb) at lengths of 4 to 4.5 m (160 to 180 in) during the 1980s, possibly representing a reduced body mass due to the species being in recovery after decades of overhunting at that stage, as males this size would typically weigh about 100 kg (220 lb) heavier.[47] Rarely very large, aged males can exceed 6 m (19 ft 8 in) in length and weigh over 1,000 kg (2,200 lb).[34][9][42]

The largest confirmed saltwater crocodile on record drowned in a fishing net in Papua New Guinea in 1979, its dried skin plus head measured 6.2 m (20 ft 4 in) long and it was estimated to have been 6.3 m (20 ft 8 in) when accounting for shrinkage and a missing tail tip.[10][9] However, according to evidence, in the form of skulls coming from some of the largest crocodiles ever shot, the maximum possible size attained by the largest members of this species is considered to be 7 m (23 ft 0 in).[10][34] A governmental study from Australia accepts that the very largest members of the species are likely to measure 6 to 7 m (19 ft 8 in to 23 ft 0 in) in length and weigh 900 to 1,500 kg (2,000 to 3,300 lb).[49] Furthermore, a research paper on the morphology and physiology of crocodilians by the same organisation estimates that saltwater crocodiles reaching sizes of 7 m (23 ft 0 in) would weigh around 2,000 kg (4,400 lb).[50] Due to extensive poaching during the 20th century, such individuals are extremely rare today in most areas, as it takes a long time for the crocodiles to attain those sizes. Also, a possible earlier presence of particular genes may have led to such large-sized saltwater crocodiles, genes that were ultimately lost from the overall gene pool due to extensive hide and trophy hunting in the past.[citation needed] However, with recent[when?] restoration of saltwater crocodile habitat and reduced poaching, the number of large crocodiles is increasing, especially in Odisha. This species is the only extant crocodilian to regularly reach or exceed 5.2 m (17 ft 1 in).[9][43] A large male from Philippines, named Lolong, was the largest saltwater crocodile ever caught and placed in captivity. He was 6.17 m (20 ft 3 in) long and weighed 1,075 kg (2,370 lb). Thought to have eaten two villagers, Lolong was captured in September 2011, and died in captivity in February 2013.[citation needed]

Female size: Adult females typically measure from 2.7 to 3.1 m (8 ft 10 in to 10 ft 2 in) in total length and weigh 76 to 103 kg (168 to 227 lb).[51][52][53] Large mature females reach 3.4 m (11 ft 2 in) and weigh up to 120 to 200 kg (260 to 440 lb).[54] The largest female on record measured about 4.3 m (14 ft 1 in) in total length.[43] Female are thus similar in size to other species of large crocodiles and average slightly smaller than females of some other species, at least the Nile crocodile.[41] The saltwater crocodile has the greatest size sexual dimorphism, by far, of any extant crocodilian, as males average about 4 to 5 times as massive as adult females and can sometimes measure twice her total length. The reason for the male skewered dimorphism in this species is not definitively known but might be correlated with sex-specific territoriality and the need for adult male saltwater crocodiles to monopolise large stretches of habitat.[55][56] Due to the extreme sexual dimorphism of the species as contrasted with the more modest size dimorphism of other species, the average length of the species is only slightly more than some other extant crocodilians at 3.8–4 m (12 ft 6 in – 13 ft 1 in).[21][31][57]

Reported sizes

Distribution and habitat

A saltwater crocodile off Maconacon, Isabela (province)
Estuarine crocodile tracks in East Timor
Saltwater crocodile jumping up at Adelaide River
Video of a jumping crocodile at Adelaide River

The saltwater crocodile inhabits coastal brackish mangrove swamps and river deltas from India's east coast, Sri Lanka and Bangladesh to Myanmar, Thailand, Malaysia, Cambodia, Vietnam, Brunei Darussalam, Indonesia, Philippines, Palau, Solomon Islands, Vanuatu and Australia's north coast.[1][2] The southernmost population in India lives in Odisha's Bhitarkanika Wildlife Sanctuary; in northern Odisha, it has not been recorded since the 1930s.[64] It occurs along the Andaman and Nicobar Islands coasts and in the Sundarbans.[65][66][67][68][69] In Sri Lanka, it occurs foremost in western and southern parts of the country.[70]

In Myanmar, it inhabits the Ayeyarwady Delta.[71] In southern Thailand, it was recorded in Phang Nga Province.[72] It is extinct in Singapore, Cambodia and Vietnam.[2][73][74]

In China, it once inhabited coastal areas from Fujian province in the north to the border of Vietnam.[75] References to crocodile attacks on humans and livestock during the Han and Song dynasties indicate that it occurred in lower Pearl River and Macau, Han River, Min River, portions of coastal Guangxi province and Hainan Island.[31]

In Sabah, it was recorded in the Klias, Segama and Kinabatangan Rivers.[76][77][78] In Sarawak, it was recorded by a camera trap in Kuching Wetlands National Park.[79] In the Lesser Sunda Islands, it is present along the coasts of Sumba, Lembata Island, Flores, Menipo, Rote Island and Timor. Its status along Alor Island is unknown, where one individual was captured in the 2010s.[80] In the Maluku Islands, it is present around the Kai Islands, the Aru Islands, and many other islands in the region, including the Torres Strait Islands. In Papua New Guinea, it is common within the coastal reaches of every river system such as the Fly River and in the Bismarck Archipelago.[81] In the Philippines, it occurs in a few coastal sites like eastern Luzon, Palawan, the Liguasan Marsh and Agusan River on Mindanao.[2]

On a beach in Darwin, Australia

In northern Australia, 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.[82][83] The saltwater crocodile population in Australia is estimated at 100,000 to 200,000 adults. Its range extends from Broome, Western Australia through the entire Northern Territory coast all the way south to Rockhampton, Queensland. The Alligator Rivers in the Arnhem Land region are misnamed due to the resemblance of the saltwater crocodile to alligators as compared to freshwater crocodiles, which also inhabit the Northern Territory.[84]

Because of its tendency to swim long distances at sea, individual saltwater crocodiles appeared occasionally in areas far away from their general range, up to Fiji.[85] Saltwater crocodiles generally spend the tropical wet season in freshwater swamps and rivers, moving downstream to estuaries in the dry season. 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 marginal river systems and sometimes into the ocean. This explains the large distribution of the species, as well as its being found in the odd places on occasion such as the Sea of Japan. Like all crocodiles, they can survive for prolonged periods in only warm temperatures, and crocodiles seasonally vacate parts of Australia if cold spells hit.[86]

Behaviour and ecology

Saltwater crocodile sunning itself
An adult saltwater crocodile swimming through a swamp

The primary behaviour to distinguish the saltwater crocodile from other crocodiles is its tendency to occupy salt water. Though other crocodiles also have salt glands that enable them to survive in saltwater, a trait which alligators do not possess, most other species do not venture out to sea except during extreme conditions.[87]

Saltwater crocodiles use ocean currents to travel long distances. In Australia, 20 crocodiles were tagged with satellite transmitters; 8 of them ventured out into open ocean, and one of them travelled 590 km (370 mi) along the coast in 25 days from the North Kennedy River on the eastern coast of Far North Queensland, around Cape York Peninsula, to the west coast in the Gulf of Carpentaria. Another individual swam 411 km (255 mi) in 20 days. Without having to move around much, sometimes simply by floating, the current-riding behaviour allows for the conservation of energy. They interrupted their movements and resided in sheltered bays for a few days until the current changed direction. Sometimes, they also swam up and down river systems.[85] While most crocodilians are social animals sharing basking spots and food, saltwater crocodiles are more territorial and are less tolerant of their own kind; adult males will share territory with females, but drive off rival males. Saltwater crocodiles mate in the wet season, laying eggs in a nest consisting of a mound of mud and vegetation. The female guards the nest and hatchlings from predators.

Generally very lethargic, a trait which helps it survive months at a time without food, the saltwater crocodile will usually loiter in the water or bask in the sun during much of the day, preferring to hunt at night. A study of seasonal saltwater crocodile behaviour in Australia indicated that they are more active and more likely to spend time in the water during the Australian summer; conversely, they are less active and spend relatively more time basking in the sun during the winter.[88] Saltwater crocodiles, however, are among the most active of all crocodilians, spending more time cruising and active, especially in water. They are much less terrestrial than most species of crocodiles, spending less time on land except for basking. At times, they tend to spend weeks at sea in search of land and in some cases, barnacles have been observed growing on crocodile scales, indicative of the long periods they spend at sea.[89]

Saltwater crocodile with a GPS-based satellite transmitter attached to its head for tracking

Despite their relative lethargy, saltwater crocodiles are agile predators and display surprising agility and speed when necessary, usually during strikes at prey. They can also swim at 24 to 29 km/h (15 to 18 mph) in short bursts, around three times as fast as the fastest human swimmers, but when cruising, they usually travel at 3 to 5 km/h (2 to 3 mph). Although stories of crocodiles being faster than a race horse for short distances across land are little more than urban legend, at the water's edge they can combine propulsion from both feet and tail to give sudden bursts of extreme speed.

While crocodilian brains are much smaller than those of mammals (as low as 0.05% of body weight in the saltwater crocodile), saltwater crocodiles are capable of learning difficult tasks with very little conditioning, learning to track the migratory route of their prey as the seasons change, and may possess a deeper communication ability than currently accepted.[90][91]

Hunting and diet

Feeding young adult in captivity, Western Australia
Saltwater crocodile tears apart a pig carcass for consumption

Like most species in the crocodilians family, saltwater crocodiles are not fastidious in their choice of food, and readily vary their prey selection according to availability, nor are they voracious, as they are able to survive on relatively little food for a prolonged period. Because of their size and distribution, saltwater crocodiles hunt the broadest range of prey species of any modern crocodilian.[86] The diet of hatchling, juvenile and subadult saltwater crocodiles has been subject to extensively greater scientific study than that of fully-grown crocodiles, in large part due to the aggression, territoriality and size of adults which make them difficult for biologists to handle without significant risk to safety, for both humans and the crocodiles themselves; the main method used for capturing adult saltwater crocodiles is a huge pole with large hooks meant for shark capture which restrict the crocodile's jaws but can cause damage to their snouts and even this is unproven to allow successful capture for crocodiles in excess of 4 m (13 ft 1 in). While for example 20th century biological studies rigorously cataloged the stomach contents of "sacrificed" adult Nile crocodiles in Africa,[92][93] few such studies were done on behalf of saltwater crocodiles despite the plethora that were slaughtered due to the leather trade during that time period. Therefore, the diet of adults is more likely to be based on reliable eye-witness accounts.[94][95][96] Hatchlings are restricted to feeding on smaller animals, such as small fish, frogs, insects and small aquatic invertebrates.[95] In addition to these prey, juveniles also take a variety of freshwater and saltwater fish, various amphibians, crustaceans, molluscs, such as large gastropods and cephalopods, birds, small to medium-sized mammals, and other reptiles, such as snakes and lizards. When crocodiles obtain a length of more than 1.2 m (3 ft 11 in), the significance of small invertebrate prey fades in favour of small vertebrates including fish and smaller mammals and birds.[97] The larger the animal grows, the greater the variety of its diet, although relatively small prey are taken throughout its lifetime.[citation needed]

Among crustacean prey, large mud crabs of the genus Scylla are frequently consumed, especially in mangrove habitats. Ground-living birds, such as the emu (Dromaius novaehollandiae) and different kinds of water birds, especially the magpie goose (Anseranas semipalmata), are the most commonly preyed upon birds, due to the increased chance of encounter.[98][99] Even swift-flying birds and bats may be snatched if close to the surface of water,[86] as well as wading birds while these are patrolling the shore looking for food, even down to the size of a common sandpiper (Actitis hypoleucos).[39][100] Mammalian prey of juveniles and subadults are usually as large as the smaller species of ungulates, such as the greater mouse-deer (Tragulus napu) and hog deer (Hyelaphus porcinus).[101] Prey species recorded include primate species such as crab-eating macaques (Macaca fascicularis),[102] proboscis monkeys (Nasalis larvatus),[103] and gibbons. It preys on agile wallabies (Macropus agilis),[104] golden jackals (Canis aureus), viverrids, turtles, flying foxes (Pteropus), hares (Lepus), rodents, badgers, otters, chevrotains and pangolins.[105][106] A rare incidence of an adult, 2.6 m saltwater crocodile preying on an Indian porcupine (Hystrix indica) was reported from Sri Lanka.[107] Unlike fish, crabs and aquatic creatures, mammals and birds are usually found only sporadically in or next to water so crocodiles seem to search for places where such prey may be concentrated, i.e. the water under a tree holding a flying fox colony or spots where herds of water buffaloes feed, in order to capture small animals disturbed by the buffalo or (if a large adult crocodile is hunting) weaker members of the buffalo herd.[99]

Studies have shown that unlike freshwater crocodiles (which can easily die from eating poisonous toads), saltwater crocodiles are partially resistant to cane toad (Rhinella marina) toxins and can consume them but in only small quantities and not enough to provide effective natural control for this virulent introduced pest.[108] Large crocodiles, even the oldest males, do not ignore small species, especially those without developed escape abilities, when the opportunity arises. On the other hand, sub-adult saltwater crocodiles weighing only 8.7 to 15.8 kg (19+1⁄4 to 34+3⁄4 lb) (and measuring 1.36 to 1.79 m (4 ft 6 in to 5 ft 10 in)) have been recorded killing and eating goats (Capra aegagrus hircus) weighing 50 to 92% of their own body mass in Orissa, India, so are capable of attacking large prey from an early age.[106][109][110] It was found the diet of specimens in juvenile to subadult range, since they feed on any animals up to their own size practically no matter how small, was more diverse than that of adults which often ignored all prey below a certain size limit.[111]

Large animals taken by adult saltwater crocodiles include sambar deer (Rusa unicolor), wild boar (Sus scrofa), Malayan tapirs (Tapirus indicus), kangaroos, humans, orangutans (Pongo ssp.), dingos (Canis lupus dingo), tigers (Panthera tigris),[112] and large bovines, such as banteng (Bos javanicus),[49] water buffalo (Bubalus arnee), and gaur (Bos gaurus).[67][113][114][115][116][117] However, larger animals are taken only sporadically due to the fact only large males typically attack very large prey and large ungulates and other sizeable wild mammals are only sparsely distributed in this species' range, outside of a few key areas such as the Sundarbans.[86] Off-setting this, goats, water buffalo and wild boar/pigs have been introduced to many of the areas occupied by saltwater crocodiles and returned to feral states to varying degrees and thus can amply support large crocodiles.[31] Any type of domestic livestock, such as chicken (Gallus gallus domesticus), sheep (Ovis aries), pigs, horses (Equus ferus caballus) and cattle (Bos primigenius taurus), and domesticated animals/pets may be eaten if given the opportunity.[86] As a seagoing species, the saltwater crocodile also preys on a variety of saltwater bony fish and other marine animals, including sea snakes, sea turtles, sea birds, dugongs (Dugong dugon), rays (including large sawfish[118]), and small sharks. Most witnessed acts of predation on marine animals have occurred in coastal waters or within sight of land, with female sea turtles and their babies caught during mating season when the turtles are closer to shore and bull sharks being the only largish shark with a strong propensity to patrol brackish and fresh waters.[86][43][119][120][121][122][123] However, there is evidence that saltwater crocodiles do hunt while out in the open seas, based upon the remains of pelagic fishes that dwell only miles away from land being found in their stomachs.[12][13]

The hunting methods utilised by saltwater crocodiles are indistinct from any other crocodilian, with the hunting crocodile submerging and quietly swimming over to the prey before pouncing upwards striking suddenly. Unlike some other crocodilians, such as American alligators and even Nile crocodiles, they are not known to have hunted on dry land.[86][31] Young saltwater crocodiles are capable of breaching their entire body into the air in a single upward motion while hunting prey that may be perched on low hanging branches.[95] While hunting rhesus macaques, they have been seen to knock the monkeys off a bank by knocking them with its tail, forcing the macaque into water for easy consumption. However, whether tail use in hunting is intentional or just an accidental benefit is not definitely clear.[31] As with other crocodilians, their sharp, peg-like teeth are well-suited to seize and tightly grip prey, but not to shear flesh. Small prey are simply swallowed whole, while larger animals are forcibly dragged into deep water and drowned or crushed.[124] Large prey is then torn into manageable pieces by "death rolling" (the spinning of the crocodile to twist off hunks of meat) or by sudden jerks of the head.[125] Occasionally, food items will be stored for later consumption once a crocodile eats its fill, although this can lead to scavenging by interlopers such as monitor lizards.[126]

Bite

Regression of mean body mass and bite force of C. porosus
Saltwater crocodiles, even adults, can breach out of the water in upwards direction to capture food, although are most often seen to do so when coerced by bait, as seen here

Saltwater crocodiles have the strongest bite of any living animal. A 4.59 metres (15 ft 1 in)* saltwater crocodile has been confirmed as having the highest bite force ever recorded for an animal in a laboratory setting, with a value of 16,414 newtons (3,690 pounds-force) (surpassing the previous record of 13,172 N or 2,961 lbf made by an American alligator (Alligator mississippinesis)).[127][128] Based on the regression of mean body mass and mean bite force, the bite forces of multiple crocodile species, 1,308 kg (2,884 lb) individuals were estimated at 27,531 to 34,424 N (6,189 to 7,739 lbf).[128] The extraordinary bite of crocodilians is a result of their anatomy. The space for the jaw muscle in the skull is very large, which is easily visible from the outside as a bulge at each side. The nature of the muscle is extremely stiff, almost as hard as bone to the touch, such that it can appear to be the continuum of the skull. Another trait is that most of the muscle in a crocodile's jaw is arranged for clamping down. Despite the strong muscles to close the jaw, crocodiles have extremely small and weak muscles to open the jaw. The jaws of a crocodile can be securely shut with several layers of duct tape.[129]

Reproduction

Saltwater crocodiles go through numerous physiological changes as they mature. Pictured here is a hatchling age or baby crocodile.
Seen here is a juvenile crocodile, which grows considerably in length over several years but is easily distinguished by slender build and size.
A saltwater crocodile in the subadult age range at Gembira Loka Zoo, similar but not as robust and relatively small-headed compared to adults.

Males reach sexual maturity around 3.3 m (10 ft 10 in) at around 16 years of age, while females reach sexual maturity at 2.1 m (6 ft 11 in) and 12–14 years of age.[10] Saltwater crocodiles mate in the wet season, when water levels are at their highest. In Australia, the male and female engage in courtship in September and October, and the female lays eggs between November and March.[49] It is possible the rising temperatures of the wet season provoke reproductive behaviour in this species.[99] While crocodilians generally nest every year, there have been several recorded cases of female saltwater crocodiles nesting only every other year and also records of a female attempting to produce two broods in a single wet season.[99] The female selects the nesting site, and both parents will defend the nesting territory, which is typically a stretch of shore along tidal rivers or freshwater areas, especially swamps. Nests are often in a surprisingly exposed location, often in mud with little to no vegetation around, and thus limited protection from the sun and wind. The nest is a mound of mud and vegetation, usually measuring 175 cm (5 ft 9 in) long and 53 cm (1 ft 9 in) high, with an entrance averaging 160 cm (5 ft 3 in) in diameter.[99] Some nests in unlikely habitats have occurred, such as rocky rubble or in a damp low-grass field.[130][131] The female crocodile usually scratches a layer of leaves and other debris around the nest entrance and this covering is reported to produce an "astonishing" amount of warmth for the eggs (coincidentally these nesting habits are similar to those of the birds known as megapodes that nest in upland areas of the same Australasian regions where saltwater crocodiles are found).[31][132]

The female typically lays from 40 to 60 eggs, but some clutches have included up to 90. The eggs measure on average 8 by 5 cm (3 by 2 in) and weigh 113 g (4 oz) on average in Australia and 121 g (4+1⁄4 oz) in India.[49][133] These are relatively small, as the average female saltwater crocodile weighs around five times as much as a freshwater crocodile, but lays eggs that are only about 20% larger in measurement and 40% heavier than those of the smaller species.[39] The average weight of a new hatchling in Australia is reportedly 69.4 g (2+7⁄16 oz).[49] Although the female guards the nest for 80 to 98 days (in extreme high and low cases from 75 to 106 days), the loss of eggs is often high due to flooding and occasionally to predation.[49] As in all crocodilians, the sex of the hatchlings is determined by temperature. At 28–30 degrees all hatchlings will be female, at 30–32 degrees 86% of hatchlings are male, and at 33 or more degrees predominantly female (84%).[134] In Australia, goannas (Varanus giganteus) commonly eat freshwater crocodile eggs (feeding on up to 95% of the clutch if discovered), but are relatively unlikely to eat saltwater crocodile eggs due to the vigilance of the imposing mother, with about 25% of the eggs being lost to goannas (less than half as many Nile crocodile eggs are estimated to be eaten by monitors in Africa).[39] A majority of the loss of eggs of saltwater crocodiles occurs due to flooding of the nest hole.[99][135]

Wild adult female saltwater crocodile.

As in most crocodilian species, the female saltwater crocodile exhibits a remarkable level of maternal care for a reptile. She excavates the nest in response to "yelping" calls from the hatchlings, and even gently rolls eggs in her mouth to assist hatching. The female will then carry the hatchlings to water in her mouth (as Nile crocodile and American alligator females have been observed doing when their eggs hatch) and remains with the young for several months. Despite her diligence, losses of baby crocodiles are heavy due to various predators and unrelated crocodiles of their own species. Only approximately 1% of the hatchlings will survive to adulthood.[136] By crocodilian standards, saltwater crocodile hatchlings are exceptionally aggressive to one another and will often fight almost immediately after being transported to water by their mother.[137] The young naturally start to disperse after around 8 months, and start to exhibit territorial behaviour at around 2.5-years-old. They are the most territorial of extant crocodilians and, due to their aggressiveness to conspecifics, from the dispersed immature stage on, they are never seen in concentrations or loose groups as are most other crocodilians.[138] However, even females will not reach proper sexual maturity for another 10 years. Saltwater crocodiles that survive to adulthood can attain a very long lifespan, with an estimated life expectancy upwards of 70 years, and some individuals possibly exceed 100 years, although no such extreme ages have been verified for any crocodilian.[10][139]

While adults have few predators, baby saltwater crocodiles may fall prey to monitor lizards (occasionally, but not commonly, the numerous goanna in Australia, and the Asian water monitor (Varanus salvator) further north), predatory fish (especially the barramundi (Lates calcarifer)), wild boars, rats, various aquatic and raptorial birds (e.g. black-necked storks (Ephippiorhynchus asiaticus) and white-bellied sea eagles (Haliaeetus leucogaster)), pythons, larger crocodiles, and many other predators.[99][49][133][135] Pigs and cattle also occasionally inadvertently trample eggs and nests on occasion and degrade habitat quality where found in numbers.[140] Juveniles may also fall prey to tigers and leopards (Panthera pardus) in certain parts of their range, although encounters between these predators are rare, and cats are likely to avoid areas with saltwater crocodiles.[141]

Conservation status

Saltwater crocodile
Large saltwater crocodile in park

The species is considered of minimal concern for extinction. Currently, the species is listed in CITES as follows:

  • Appendix I (prohibiting all commercial trade in the species or its byproducts): All wild populations except for those of Australia, Indonesia and Papua New Guinea;
  • Appendix II (commercial trade allowed with export permit; import permits may or may not be required depending on the laws of the importing country): Australia, Indonesia and Papua New Guinea wild populations, plus all worldwide populations bred in captivity for commercial purposes.

The saltwater crocodile was often hunted for its meat and eggs, and its skin is the most commercially valuable of any crocodilian. Unregulated hunting during the 20th century caused a dramatic decline in the species throughout its range, with the population in northern Australia reduced by 95% by 1971. The years from 1940 to 1970 were the peak of unregulated hunting and may have regionally caused irreparable damage to saltwater crocodile populations.[142] The species currently has full legal protection in all Australian states and territories where it is found – Western Australia (since 1970), Northern Territory (since 1971) and Queensland (since 1974).[143] Illegal hunting still persists in some areas, with protection in some countries being grossly ineffective, and trade is often difficult to monitor and control over such a vast range. However, many areas have not recovered; some population surveys have shown that although young crocodiles are present, fewer than 10% of specimens spotted are in adult size range and do not include any particularly large males, such as Sri Lanka or the Republic of Palau. This is indicative of both potential continued persecution and exploitation and a non-recovered breeding population.[144][145] In a more balanced population, such as those from Bhitarkanika National Park or Sabah on Borneo, 28% and 24.2% of specimens observed were in the adult size range of more than 3 m (9 ft 10 in).[76][146]

Habitat loss continues to be a major problem for the species. In northern Australia, much of the nesting habitat of the saltwater crocodile is susceptible to trampling by feral water buffalo, although buffalo eradication programs have now reduced this problem considerably. 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 to human agriculture. After the commercial value of crocodile skins waned, perhaps the greatest immediate challenge to implementing conservation efforts has been the occasional danger the species can pose to humans, and the resulting negative view of the crocodile.[136][147]

Relationship with humans

Attacks on humans

See also: Crocodile attack

Of all the crocodilians, the saltwater crocodile and Nile crocodile have the strongest tendencies to treat humans as prey.[148] The saltwater crocodile has a long history of attacking humans who unknowingly venture into its territory. As a result of its power, intimidating size and speed, survival of a direct predatory attack is unlikely if the crocodile is able to make direct contact. By contrast to the American policy of encouraging a certain degree of habitat coexistence with alligators, the only recommended policy for dealing with saltwater crocodiles is to completely avoid their habitat whenever possible, as they are exceedingly aggressive when encroached upon.[31]

No Swimming sign used by Parks and Wildlife Commission of the Northern Territory.[149]

Exact data on attacks are limited outside Australia, where one or two fatal attacks are reported per year.[150] From 1971 to 2013, the total number of fatalities reported in Australia due to saltwater crocodile attack was 106.[151][150] The low level of attacks may be due to extensive efforts by wildlife officials in Australia to post crocodile warning signs at numerous at-risk billabongs, rivers, lakes and beaches.[152] Less-publicised attacks have been reported in Borneo,[153] Sumatra,[154] Eastern India (Andaman Islands),[155][156] and Burma.[157] In Sarawak, Borneo, the average number of fatal attacks is reportedly 2.8 annually for the years from 2000 to 2003.[158] In the Northern Territory in Australia, attempts have been made to relocate saltwater crocodiles who have displayed aggressive behaviour towards humans but these have proven ineffective as the problem crocodiles are apparently able to find their way back to their original territories.[159] In the Darwin area from 2007–2009, 67–78% of "problem crocodiles" were identified as males.[160]

Many attacks in areas outside Australia are believed to go unreported, with one study positing up to 20 to 30 attacks occur every year.[158] This number may be conservative in light of several areas where humans and saltwater crocodiles co-exist in relatively undeveloped, low-economy and rural regions, where attacks are likely to go unreported.[148] However, claims in the past that saltwater crocodiles are responsible for thousands of human fatalities annually are likely to have been exaggerations and were probably falsified to benefit leather companies, hunting organisations and other sources which may have benefited from maximising the negative perception of crocodiles for financial gain.[31][43][158] Although it does not pay to underestimate such a formidable predator, one that has no reason to not view humans as prey, many wild saltwater crocodiles are normally quite wary of humans and will go out of their way to submerge and swim away from them, even large adult males, if previously subject to harassment or persecution.[161][162] Some attacks on humans appear to be territorial rather than predatory in nature, with crocodiles over two years in age often attacking anything that comes into their area (including boats). Humans can usually escape alive from such encounters, which comprise about half of all attacks. Non-fatal attacks usually involve crocodiles of 3 m (9 ft 10 in) or less in length. Fatal attacks, more likely to be predatory in motivation, commonly involve larger crocodiles with an average estimated size of 4.3 m (14 ft 1 in). Under normal circumstances, Nile crocodiles are believed to be responsible for a considerably greater number of fatal attacks on humans than saltwater crocodiles, but this may have more to do with the fact that many people in Africa tend to rely on riparian areas for their livelihood, which is less prevalent in most of Asia and certainly less so in Australia.[158] In the Andaman Islands, the number of fatal attacks on humans has reportedly increased, the reason inferred due to habitat destruction and reduction of natural prey.[163]

During the Japanese retreat in the Battle of Ramree Island on 19 February 1945, saltwater crocodiles may have been responsible for the deaths of over 400 Japanese soldiers. British soldiers encircled the swampland through which the Japanese were retreating, condemning the Japanese to a night in the mangroves, which were home to thousands of saltwater crocodiles. Many Japanese soldiers did not survive this night, but their death mainly as a result of crocodile attacks has been doubted.[164] Another reported mass attack reportedly involve a cruise in eastern India where a boat accident forced 28 people into the water where they were reportedly consumed by saltwater crocodiles.[43] Another notorious crocodile attack was in 1985, on ecofeminist Val Plumwood, who survived the attack.[165][166]

In July 2018, a 600-strong mob slaughtered 292 saltwater and New Guinea crocodiles in Papua province in Indonesia in a revenge attack after a man who encroached the sanctuary was devoured.[167]

Cultural references

1948 postage stamp depicting an aboriginal artwork of the saltwater crocodile

The saltwater crocodile is considered holy on Timor. According to legend, the island was formed by a giant crocodile. The Papuan people have a similar and very involved myth and traditionally the crocodile was described as a relative (normally a father or grandfather).[31]

According to Wondjina, the mythology of Indigenous Australians, the saltwater crocodile was banished from the fresh water for becoming full of bad spirits and growing too large, unlike the freshwater crocodile, which was somewhat revered.[168] Aboriginal rock art depicting the saltwater crocodile is rare, although examples of up to 3,000 years old were found in caves in Kakadu and Arnhem land, roughly matching the distribution of the species. It is however depicted in contemporary aboriginal art.[169] The Larrakia people think of themselves as crocodile descendants, and regard it as their totem. They respect crocodiles as protectors of harbours and do not eat crocodile meat.[170]

The species is featured on several postage stamps, including an 1894 State of North Borneo 12-cent stamp; a 1948 Australian 2 shilling stamp depicting an aboriginal rock artwork of the species; a 1966 Republic of Indonesia stamp; a 1994 Palau 20-cent stamp; a 1997 Australian 22-cent stamp; and a 2005 1 Malaysian ringgit postage stamp.

The saltwater crocodile has featured in contemporary Australian film and television including the "Crocodile" Dundee series of films and The Crocodile Hunter television series. There are now several saltwater crocodile-themed parks in Australia.[citation needed]

Examples of large unconfirmed saltwater crocodiles

Large saltwater crocodiles have always attracted mainstream attention throughout the ages, and have suffered from all sorts of big fish stories and hunter tales, due to man's desire to find the largest of any given thing. Therefore, the largest size recorded for a saltwater crocodile has always been a subject of considerable controversy. The reason behind unverified sizes is either the case of insufficient/inconclusive data or exaggeration from a folkloric point of view. This section is dedicated to examples of the largest saltwater crocodiles recorded outside scientific norms measurement and estimation, with the aim of satisfying the public interest without creating data pollution, as well as serving an educational purpose of guiding the reader to separate fact from possible fiction. Below, in descending order starting from the largest, are some examples of large unconfirmed saltwater crocodiles, recorded throughout history.

  • A crocodile shot in the Bay of Bengal in 1840 was reported at 10.1 m (33 ft 2 in). Furthermore, this specimen was claimed to have a belly girth of 4.17 m (13 ft 8 in) and a body mass estimated 3,000 kg (6,600 lb). However, the skull of this specimen was examined by Guinness Records and found to be only 66.5 cm (2 ft 2+1⁄4 in) in length, indicating the above size was considerably exaggerated and the animal would have probably measured no more than 5.89 m (19 ft 4 in).[43]
  • James R. Montgomery, who ran a plantation near to the Lower Kinabatangan Segama Wetlands in Borneo from 1926 to 1932, claimed to have netted, killed, and examined numerous crocodiles well over 6.1 m (20 ft 0 in) there, including a specimen he claims measured 10 m (32 ft 10 in). However, no one scientifically confirmed any of Montgomery's specimens and no voucher specimens are known.[43]
  • A crocodile shot in Queensland in 1957, nicknamed Krys the croc (named after the woman that shot the crocodile in July 1957; Krystina Pawlowski), was reported to be 8.63 m (28 ft 4 in) long, but no verified measurements were made and no remains of this crocodile exist.[171][172] A "replica" of this crocodile has been made as a tourist attraction.[173][174][175]
  • A crocodile killed in 1823 at Jalajala on the main island of Luzon in the Philippines was reported at 8.2 m (26 ft 11 in). However the skull of the specimen is 66.5 cm (26+1⁄4 in) long indicating an animal of approximately 6.1 m (20 ft 0 in).[43]
  • A crocodile shot in Odisha, India,[176] was claimed to measure 7.6 m (24 ft 11 in) in life, but its skull, when given scholarly examination, was thought to have come from a crocodile of a length no greater than 7 m (23 ft 0 in).[177]
  • A reported 7.6 m (24 ft 11 in) crocodile was killed in the Hooghly River in the Alipore District of Calcutta. However, examinations of the animal's skull, one of the largest skulls known to exist for the species at 75 cm (30 in) long, actually indicating it could have measured 6.7 m (22 ft 0 in).[43]
  • In 2006, Guinness accepted a 7.01 m (23 ft 0 in), 2,000-kilogram (4,400 lb) male saltwater crocodile living within Bhitarkanika Park in Odisha. Due to the difficulty of trapping and measuring a very large living crocodile, the accuracy of these dimensions is yet to be verified. These observations and estimations have been made by park officials over the course of ten years, from 2006 to 2016, however, regardless of the skill of the observers it cannot be compared to a verified tape measurement, especially considering the uncertainty inherent in visual size estimation in the wild.[178] In addition, this region may contain up to four other specimens measuring over 6.1 m (20 ft 0 in).[176][179]
  • S. Baker (1874) claimed that in Sri Lanka in the 1800s, specimens measuring 6.7 m (22 ft 0 in) or more were commonplace.[43] However, the largest specimen killed on the island that was considered authentic by Guinness Records was a suspected man-eater killed in the Eastern Province and measuring exactly 6 m (19 ft 8 in) in length.[43]
  • The record size for a crocodile from Papua New Guinea to be considered authentic by Guinness was a 6.32 m (20 ft 9 in) specimen shot by Herb Schweighofer in May 1966 along the northeastern coast. This specimen had a belly girth of 2.74 m (9 ft 0 in).[43]

See also

References

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