The saltwater crocodiles are the largest crocodilians in existence, in addition to being highly opportunistic and territorial predators when compared to other crocodilians. They have a strong tendency to treat humans in their territory as prey, and have a long history of attacking and consuming humans who stray into their territory. Therefore, the only safe policy for dealing with saltwater crocodiles is to avoid their territory whenever possible as they tend to be highly aggressive when encroached upon
An adult male saltwater crocodile’s weight on average is 409 to 1,000 kilograms and length is normally 4.1 to 5.5 metres. However, mature males have been known to exceed 6 metres and weigh more than 1,000 kilograms, and this species is the only extant crocodilian to regularly reach or exceed 4.8 metres. Weight can vary enormously based upon the condition and age; older males tend to outweigh younger ones since they maintain prime territories with access to better, more abundant prey. This species has the greatest sexual dimorphism of any modern crocodilian, with the females being much smaller than males. Typical female body lengths range from 2.3 to 3.5 metres. The largest female on record measured about 4.2 metres. The mean weight of the species as a whole is roughly 450 kilograms.
Saltwater crocodiles have very large heads. A pair of ridges run from the eyes along the center of the snout. The eyes, ears, and nostrils are located on the same plane on the top of the head, allowing for it to see, hear, and breathe while almost totally submerged. The eyes have a special second pair of eyelids known as the nictitating membrane. These eyelids are clear and protect the eyes while underwater. The ears, situated behind the eyes, have flaps which also close while underwater. The jaws are heavy set and contain between 64-68 teeth. The teeth in the upper jaw are perfectly aligned with those in the lower jaw. The fourth tooth on each side of the bottom jaw is larger than the other teeth and is visible when the mouth is closed.
Juvenile saltwater crocodiles are yellow in colour with black stripes and spots. As they mature, the colour becomes paler and the stripes indistinct until they disappear. Adults are dark in colour with light grey areas. The belly is yellowish and the underside of the tail is grey near the tip. Dark bands are located on the lower flanks. The hide lacks osteoderms (bony plates) and is ideal for tanning in the leather industry. Scales are oval in shape and the scutes are small. The colouration of this species differs in regions; some areas have juveniles much lighter in colour than elsewhere.
Saltwater crocodiles can swim at 15 to 18 miles per hour in short bursts, but when cruising they go at 2 to 3 mph.
Saltwater crocodiles are considered very intelligent and sophisticated animals. They communicate by barks and are thought to display four different calls, including a high-pitched distress call performed by juveniles in a series of short barks. Threat calls consist of a hissing sound made at intruders. The courtship bellow is heard as a long, low growl.
Saltwater crocodiles use thermoregulation to maintain body temperatures. They cool themselves in water and warm themselves in the sun.
The saltwater crocodile is an apex predator capable of taking nearly any animal that enters its territory, either in the water or on dry land. They are known to attack humans who enter the crocodiles’ territory. 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 (especially fish) make up an important part of the diet even in adults. Large adult saltwater crocodiles can potentially eat any animals within their range, including monkeys, kangaroos, wild boar, dingos, birds, domestic livestock, pets, humans, wild boar, bats, and even sharks.
Generally very lethargic, a trait which helps it survive months at a time without food it loiters in the water or basks in the sun through much of the day, preferring to hunt at night. Saltwater crocodiles are capable of explosive bursts of speed when launching an attack from the water.
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.
Its typical hunting technique is known as 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 the large animals once they are dead.
Breeding and raising of the young saltwater crocodiles actually happens in freshwater areas, the female lays between 40 – 60 eggs in a nest made from plant matter and mud on a river bank which is elevated to avoid loss from flooding during the rainy season. The mother guards the nest, even preventing it from drying out if necessary by splashing it with water. The eggs take 90 days to develop. The sex of the young saltwater crocodiles is determined by the incubation temperature. Below 30°C the hatchlings will be female, and above 32°C they will be male.
When eggs are about to hatch the baby crocodiles make chirping sounds, and the mother helps them by digging them out of the nest. Then she takes the hatchlings to the water’s edge in her mouth and from here on watches over them until they are able to look after themselves.
Not all of the newborn crocodiles will reach adulthood, less than 1% will not survive. Predation by turtles takes its toll in the early days, and later on the juveniles are often killed and eaten by territorial mature males.
Newly hatched saltwater crocodiles measure about 25 to 30 centimetres long and weigh an average of 70 grams. Males reach sexual maturity at around 3.3 metres at around 16 years of age, while females reach sexual maturity at 2.1 metres and 12–14 years. The average lifespan for the saltwater crocodiles is up to 70 years.
The territorial behaviour of the male saltwater crocodiles forces the young crocodiles out of the region in which they have been raised. They have to find an unoccupied territory for themselves. If they are unable to do that they will either be killed or be forced out to sea. Here they will move around until they find another river system.
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.
While these species do have a fairly large habitation area, we only visit a few of those areas – as their habitat and our diving rarely overlap. Some of our expeditions have brought us to their habitat, but we take care not to intrude. They are not encoutnered at all aboard our Similan Liveaboard
Extensive hunting for their hides (the most valuable of all crocodile skins) has reduced the population of saltwater crocodiles numbers to a critical level. Their reputation as a man-eater doesn’t help either. The two facts combined have resulted in crocodiles numbers dwindling to almost zero in countries that previously had healthy populations.
When saltwater crocodiles were finally made a protected species their numbers slowly recovered. Today several breeding programs exist, for skin and meat production. For this crocodile eggs are collected from the wild. The egg collection so far hasn’t shown any detrimental effect on the population numbers.
Aggressive trapping of problem crocodiles and their removal to crocodile farms has reduced the numbers of conflicts between humans and reptiles.
Population estimates range from 200,000 to 300,000 worldwide, and they are considered at low risk for extinction. But saltwater crocodile hides are valued above all other crocodilians, and illegal hunting, habitat loss, and antipathy toward the species because of its reputation as a man-eater continue to put pressure on the population.