Saltwater crocodile

Appearance

The saltwater crocodile has a wide snout compared to most crocodiles. However, it has a longer muzzle than the mugger crocodile; its length is twice its width at the base. The saltwater crocodile has fewer armour plates on its neck than other crocodilians. On this species, 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. 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. The head is very large. The largest skull sized that could be scientifically verified was for a specimen in the Muséum national d'Histoire naturelle sourced to Cambodia, the skull length for this specimen was 76 cm are exceptional), with a mandibular length of 98.3 cm and a maximum width across the skull of 48 cm. The length of the specimen this came from 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 range. Although it is the largest overall living crocodilian and reptile, other crocodilians may have a proportionately longer skull, namely the gharial and the false gharial, skull lengths in the latter have been verified up to 84 cm, although both of these thin-snouted species have less massive skulls and considerably less massive bodies than the saltwater crocodile. The teeth are also long, with the largest teeth having been measured at up to 9 cm in length. If detached from the body, the head of a very large male crocodile can reportedly weigh over 200 kg alone, including the large muscles and tendons at the base of the skull that lend the crocodile its massive biting strength.

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 on 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.

Distribution

The saltwater crocodile is one of the three crocodilians found in India, the other two being the more regionally widespread, smaller mugger crocodile and the narrow-snouted, fish-eating gharial. Apart from the eastern coast of India, the saltwater crocodile is extremely rare on the Indian subcontinent. A large population is present within the Bhitarkanika Wildlife Sanctuary of Odisha and they are known to be present in smaller numbers throughout the Indian and Bangladeshi portions of the Sundarbans. The saltwater crocodile also persists in bordering Bangladesh as does the mugger and gharial. Populations are also present within the mangrove forests and other coastal areas of the Andaman and Nicobar Islands in India. Saltwater crocodiles were once present throughout most of the island of Sri Lanka, but remain mostly within protected areas such as Yala National Park, which also has a large population of mugger crocodiles.

In northern Australia, 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. The saltwater crocodile population in Australia is estimated at 100,000 to 200,000 adults. In Australia, the species coexists with the smaller, narrow-snouted Johnston's or freshwater crocodile. Their range extends from Broome in Western Australia through the entire Northern Territory coast all the way south to Rockhampton in 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. In New Guinea, they are also common, existing within the coastal reaches of virtually every river system in the country, such as the Fly River, along with all estuaries and mangroves, where they overlap in range but rarely in actuality or habitat with the rarer, less aggressive New Guinea crocodile. They are also present in varying numbers throughout the Bismarck Archipelago, the Kai Islands, the Aru Islands, the Maluku Islands and many other islands within the region, including Timor, and most islands within the Torres Strait.

The saltwater crocodile was historically known to be widespread throughout Southeast Asia, but is now extinct throughout much of this range. This species has not been reported in the wild for decades in most of Indochina and is extinct in Thailand, Laos, Vietnam, and possibly Cambodia. The status of this species is critical within much of Myanmar, but a stable population of many large adults is present in the Irrawaddy Delta. Probably, the only country in Indochina still harbouring wild populations of this species is Myanmar. Although saltwater crocodiles were once very common in the Mekong Delta and other river systems, the future of this species in Indochina is now looking grim. However, it is also the least likely of crocodilians to become globally extinct due to its wide distribution and almost precolonial population sizes in Northern Australia and New Guinea.

The saltwater crocodile has been long extinct in China, where it inhabited the southern coastal areas from Fujian province in the north to the border of Vietnam. References to large crocodiles that preyed on both humans and livestock appeared during the Han and Song Dynasties, where it occurred in the lower Pearl River near present-day Hong Kong and Macau, the Han River, the Min River in the north, portions of coastal Guangxi province and Hainan Island. The presence of crocodiles in Fujian province represent the northernmost distribution of the species.

The population is sporadic in Indonesia the Philippines and Malaysia, with some areas harbouring large populations and others with very small, at-risk populations. Despite the close proximity to the crocodile hotbed of northern Australia, crocodiles no longer exist in Bali. This species is also reportedly extinct on Lombok, Komodo, and most of Java. In the southern Malaysian Peninsula as well as Borneo, salwater crocodiles may co-exist with the relatively narrow-snouted false gharial and the closely related but usually smaller Siamese crocodile. A small population may remain within Ujung Kulon National Park in western Java. 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 and soon to be extinct population in Vanuatu and a decent but at-risk population in Palau. They once ranged as far west as the east coast of Africa to the Seychelles Islands. These crocodiles were once believed to be a population of Nile crocodiles, but they were later proven to be "C. porosus".

The saltwater crocodile has been extirpated from much of its former range within the Philippines and currently populations remain in only a few scattered locations. On the island of Mindanao the species is present within the Ligawasan Marsh and adjacent waterways in the southwest of the island and also within the Agusan Marsh Wildlife Sanctuary in the eastern portion of the island, where in September of 2011 a 20.24 foot/6.17 meter saltwater crocodile, the largest reliably measured, was captured by locals following two fatal attacks. This species is also reported to be found within the mangroves of Languyan Island of the Tawi-Tawi province southwest of Mindanao and within the mangroves of Del Carmen municipality on Siargao Island northeast of Mindanao. On Luzon Island the species has been reported from three areas in the northeast: the Blos River of barangay Reina Mercedes, the Divilacan mangroves of barangay Dimasalansan and the Palanan River estuary of barangay Culasi. On the island of Palawan the species appears to remain within only the southern portion of the country and in recent years, attacks on humans have occurred within the Rio Tuba area near Bataraza on the southeast coast and from near Rizal on the southeastern coast. The species is also reported to be present within the islands of the Balabac Strait between the island of Palawan and the Malaysian Borneo state of Sabah. The status of the species within Naujan Lake on the island of Mindoro is unclear; crocodile eye-shines have been spotted in recent years and these are believed to belong to the saltwater crocodile, but it is unknown whether a viable population remains.

Because of its tendency to travel very long distances at sea, individual saltwater crocodiles have been known to appear occasionally in areas far away from their general range. Vagrant individuals have historically been reported on New Caledonia, Fiji, and in Asian waters possibly swam with Kuroshio Current, reaching such as at Iwo Jima, Hachijō-jima, Amami Ōshima, Iriomote-jima, pelagic waters off Shima, Mie, Miura Peninsula, and even in the relatively frigid Sea of Japan In late 2008-early 2009, a handful of wild saltwater crocodiles were verified to be living within the river systems of Fraser Island, hundreds of kilometres from, and in much cooler water than, their normal Queensland range. These crocodiles did indeed migrate south to the island from northern Queensland during the warmer wet season and presumably returned to the north upon the seasonal temperature drop. Despite the surprise and shock within the Fraser Island public, this is apparently not new behaviour, and in the distant past, wild crocodiles had been reported appearing occasionally as far south as Brisbane during the warmer wet season.

Saltwater crocodiles generally spend the tropical wet season in freshwater swamps and rivers, moving downstream to estuaries in the dry season, and sometimes travelling 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, as well as its being found in the odd places on occasion. Like all crocodiles, they can survive for prolonged periods in only warm temperatures, and crocodiles seasonally vacate parts of Australia if cold spells hit.

Behavior

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. The only other species to display regular seagoing behaviour is the American crocodile, but the American version is still not considered to be as marine-prone as the saltwater crocodile. As its alternate name "sea-going crocodile" implies, this species travels between areas separated by sea, or simply relies on the relative ease of travelling through water in order to circumvent long distances on the same land mass, such as Australia. In a similar fashion to migratory birds using thermal columns, saltwater crocodiles use ocean currents to travel long distances. In a study, 20 crocodiles were tagged with satellite transmitters; 8 of these crocodiles ventured out into open ocean, in which one of them travelled 590 km along the coast – from the North Kennedy River on eastern coast of Far North Queensland, around Cape York Peninsula, to the west coast in the Gulf of Carpentaria – in 25 days. Another specimen, a 4.84 m -long male, travelled 411 km in 20 days. Without having to move around much, sometimes simply by floating, the current-riding behaviour allows for the conservation of energy. They will even interrupt their travels, residing in sheltered bays for a few days, when the current is against the desired direction of travel, until the current changes direction. Crocodiles also travel up and down in river systems, periodically.

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. 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.

Despite their relative lethargy, saltwater crocodiles are agile predators and display surprising agility and speed when necessary, usually during strikes at prey. They are capable of explosive bursts of speed when launching an attack from the water. They can also swim at 15 to 18 mph in short bursts, around three times as fast as the fastest human swimmers, but when cruising, they usually go at 2 to 3 mph. However, 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, however, where they can combine propulsion from both feet and tail, their speed can be explosive.

While crocodilian brains are much smaller than those of mammals, 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.

Reproduction

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. It is possible the rising temperatures of the wet season provoke reproductive behaviour in this species. 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. 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 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 long and 53 cm high, with an entrance averaging 160 cm in diameter. Some nests in unlikely habitats have occurred, such as rocky rubble or in a damp low-grass field. 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. 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 and weigh 113 g on average in Australia and 121 g in India. 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. The average weight of a new hatchling in Australia is reportedly 69.4 g. Although the female guards the nest for 80 to 98 days, the loss of eggs is often high due to flooding and occasionally to predation. 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. In Australia, goannas commonly eat freshwater crocodile eggs, 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. A majority of the loss of eggs in the saltwater crocodile occurs due to flooding of the nest hole.

As in all 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 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. 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. The young naturally start to disperse after around 8 months, and start to exhibit territorial behaviour at around 2.5-year-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. 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. While adults have few predators, baby saltwater crocodiles may fall prey to monitor lizards further north), predatory fish ), wild boars, rats, various aquatic and raptorial birds and white-bellied sea eagles ), pythons, larger crocodiles, and many other predators. Pigs and cattle also occasionally inadvertently trample eggs and nests on occasion and degrade habitat quality where found in numbers. Juveniles may also fall prey to tigers and leopards in certain parts of their range, although encounters between these predators are rare and cats are likely to avoid areas with saltwater crocodiles.

Food

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. 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. While for example 20th century biological studies rigorously cataloged the stomach contents of "sacrificed" adult Nile crocodiles in Africa, 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. Hatchlings are restricted to feeding on smaller animals, such as small fish, frogs, insects and small aquatic invertebrates. 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, the significance of small invertebrate prey fades in favor of small vertebrates including fish and smaller mammals and birds. The larger the animal grows, the greater the variety of its diet, although relatively small prey are taken throughout its lifetime.

Among crustacean prey, large mud crabs of the genus "Scylla" are frequently consumed, especially in mangrove habitats. Ground-living birds, such as the emu and different kinds of water birds, especially the magpie goose, are the most commonly preyed upon birds, due to the increased chance of encounter. Even swift-flying birds and bats may be snatched if close to the surface of water, as well as wading birds while these are patrolling the shore looking for food, even down to the size of a common sandpiper. Mammalian prey of juveniles and subadults are usually as large as the smaller species of ungulates, such as the greater mouse-deer and hog deer. Various mammalian species including monkeys, long-tailed macaques & proboscis monkeys,), gibbons, porcupines, wallabies,...hieroglyph snipped... mongoose, civets, jackals, turtles, flying foxes, hares, rodents, badgers, otters, fishing cats and chevrotains are readily taken when encountered. 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 weaker members of the buffalo herd. Studies have shown that unlike freshwater crocodiles, saltwater crocodiles are partially resistant to cane toad toxins and can consume them but in only small quantities and not enough to provide effective natural control for this virulent introduced pest. 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 ) have been recorded killing and eating goats weighing 50 to 92% of their own body mass in Orissa, India, so are capable of attacking large prey from an early age. 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.

Large animals taken by adult crocodiles include sambar deer, wild boar, Malayan tapirs, kangaroos, orangutans, dingos, tigers, and large bovines, such as banteng, water buffalo, and gaur. 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. 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. Any type of domestic livestock, such as chicken, sheep, pigs, horses and cattle, and domesticated animals/pets may be eaten if given the opportunity. 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, rays, 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. 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.

The hunting methods utilized 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 alligators and even Nile crocodiles, they are not known to have hunted on dry land. 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. While hunting rhesus macaques, crocodiles have been seen to knock the monkeys off a bank by knocking them with their 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. As with other crocodilians, their sharp, peg-like teeth are well-suited to seize and tightly grip prey, but not designed to shear flesh. Small prey are simply swallowed whole, while larger animals are forcibly dragged into deep water and drowned or crushed. Large prey is then torn into manageable pieces by "death rolling" or by sudden jerks of the head. 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.