The Saltwater crocodile, crocodilus porosus, is also known as the estuarine crocodile. The term porsus comes from the Greek porosis meaning full of calloses and refers to the bumpy nature of the upper surfaces of the body. The word crocodile originates from Greek krokodilos meaning “worm of the stones”, referring to their habit of basking on pebbles at the waters’ edge. In Australia the species is commonly refered to as ‘Salties’.
There are thirteen subspecies of the genus crocodylidae, two of which, the freshwater and the saltwater, are found in Australia. Crocodilus porosus is found around south east Asia from India to Australia. In Australia it is found from south-east Queensland around the top-end to north-east WA. It frequents coastal waters, rivers and billabongs (ox-bow lakes) up to 200km inland and have been known to travel 1000km by sea.
At up to 7 metres in length and one tonne in mass, it is the largest extant example of the species and the largest surviving reptile in terms of mass. However, specimens over 5 metres long are very rare and at their average length the weight will be closer to 500Kg. Females are smaller, generally reaching a maximum length of 3 metres.
Young salties have a pale yellow colouration with dark spots and stripes. After many years they become darker with lighter areas visible, the underside being a creamy white. Colouration does, however, vary with area. They have a pair of ridges running from the eyes to the snout which become more distinct with age and have oval shaped scales
Thay have particularly large heads and strong jaws (strong enough to crush a buffalo skull) and the ears, nose and eyes are all on the top of the head, allowing these senses to be used whilst almost completely submerged. The eyes have a nictitating membrane which act as a second, clear, set of eyelids, giving protected underwater vision.
Crocodiles spend most of the time basking in order to regulate body temperature (at 30 to 32 degrees C) and defending a territory by the use of postures and low-frequency vocalizations. Fights are rare.
Maximum lifespan is at least 70 years, possibly over 100.
Saltwater crocodiles are carnivores whose choice of meat depends purely upon the size of the prey that they are able to catch. Hence fully grown adults can take prey the size of a buffalo and smaller, young crocs will prey mainly on crabs and other small crustaceans, as well as small fish and insects. Large salties will also take humans, although this is very rare (14 deaths in 27 years since protection was introduced) and usually due to a lack of care by the human.
Attack is normally from the waters’ edge and is extremely rapid. Prey is then normally dragged back to the water where it is drowned, although when multiple crocodiles are involved death may be by dismemberment. Larger prey will be torn to small pieces before swallowing above water to avoid ingestion of large amounts of water. Hunting is normally at night.
Stones and pebbles are often ingested to aid with digestion and for ballast.
Female salties reach maturity at 12-14 years old, males a couple of years later. Reproduction occurs annually. Mating takes place in September/October, after which a nest will be constructed close to water (so that the female can remain attentive and still feed). The nest is a mound of plant material and mud and serves the purpose of incubating the 40-60 eggs that are laid. The sex of the offspring is determined by the temperature at which the eggs are kept, 31.6 degrees C produces mainly males, slightly above and below that produces females. Above 34 degrees all the eggs will die.
Eggs hatch after 80 days and at this time the offspring are no more than 29cm long. When the first eggs hatch the young produce a characteristic yelping sound. This leads to the mother digging out the eggs, gently breaking open the un-hatched eggs, and carrying the young to the water in her mouth. The young will be raised in fresh water.
Approximately 80% of the eggs will be lost before hatching as a result of being submerged by rising water, being eaten by goannas or feral pigs or by being trampled on by buffalo. Once hatched most of the hatchlings will be taken by fish, birds and turtles and by non-parental adult crocodiles. Normally less than 1% of the hatchlings will reach maturity, meaning that only one newborn will survive every 2 or 3 years.
Legal hunting of saltwater crocodiles was stopped in the early 1970’s in Australia due to the near complete collapse of the population and as a consequence numbers have increased dramatically. It is thought that the population is around 100,000 to 150,000 and this population is regarded as secure. Limited numbers of crocodiles can be legally taken by indigenous Australians. There is talk of introducing “safari-style” hunting of crocodiles but so far this has been resisted.
Crocodiles suffer from their image as ‘man-eaters’ and there is concern from some quarters that there are now too many crocodiles. For this reason care needs to be taken not to allow the return of widespread hunting.
http://flmnh.ufl.edu/cnhc/csp_cpor.htm the crocodilian species list
Wilson and Swan, The Complete Guide to Reptiles of Australia