Crocodiles have been around for 200 million years and are a descendant from the dinosaur age.
In the Northern Territory (NT) common names for saltwater crocodiles include estuarine crocodile, saltie and croc. There are also many different Indigenous language names for saltwater crocodiles.
The scientific name for saltwater crocodiles is Crocodylus porosus.
Size of saltwater crocodiles
The saltwater crocodile is the largest living reptile species. It can grow up to 6m and is a serious threat to humans.
Females usually reach maturity when around 2.3m in length. Males mature at around 3.3m. Farmed crocodiles grow faster and mature earlier that those in the wild.
The average saltwater crocodile egg weighs 110g and the average hatchling weighs 70g at a total length of 29cm. Their head length is 4cm and snout to cloaca length is 14cm.
Hunting ability of crocodiles
Large saltwater crocodiles can stay underwater for up to one hour because they can reduce their heart rate to two to three beats per minute.
This means that saltwater crocodiles can wait underwater until prey either swims nearby or approaches the water's edge.
Crocodiles have a 'minimum exposure' posture in the water, which means that only their sensory organs - eyes, cranial platform, ears and nostrils - stay out of the water. This means that they often go unseen by prey, but if they are seen it is hard to tell how big the crocodile is.
Crocodiles have special nerve endings on their jaws and on the underside of their body that help them to detect the movement of prey in the water.
About the crocodile body
The tail of a crocodile is solid muscle and a major source of power, making it a strong swimmer and able to make sudden lunges out of the water to capture prey. These strong muscles also mean that for shorts bursts of time crocodiles can move faster than humans can on land.
Crocodiles have a thin layer of guanine crystals behind their retina. This intensifies images, allowing crocodiles to see better at low light levels.
Hearing and smell
A crocodile's sense of hearing and smell is excellent when their head is above the water. This helps to locate prey, especially in poor light or low visibility.
Teeth and jaw
While crocodiles may regularly lose teeth, they have a second tooth sitting in reserve underneath the external tooth, which can replace the lost tooth.
What crocodiles eat
The size of the saltwater crocodile prey is only limited by the crocodiles own size and strength.
Saltwater crocodiles mostly eat fish, but will eat almost anything that they can overpower which can include turtles, goannas, snakes, birds, livestock such as cattle, buffalo, wild boar and mud crabs.
Hatchlings and juvenile saltwater crocodiles feed on insects, crustaceans, small reptiles, frogs and small fish.
Breeding season of crocodiles
Saltwater crocodiles reach sexual maturity at 12 years for females and males at 16 years.
Females build mound nests from vegetation between November and May, and an average of 50 eggs are laid.
At 28°C to 30°C, 100% of eggs will be female. At 31°C, 50% will be female and 50% male. At 32°C, 100% of eggs will be male, and at 33°C to 34°C females will vary between 50% to 100%.
The eggs hatch from 75 days.
On average, only 25% of eggs will hatch and 54% of the hatchlings will survive the first year.
Only 1% of hatchlings are thought to survive to maturity in the wild.
Biggest crocodiles reported and caught
A 6.4m saltwater crocodile was caught in a net on the Mary River in 1974. The animal was killed and its head removed by an axe.
The biggest saltwater crocodile ever caught in a trap was just over 5m.
The biggest saltwater crocodile harpooned by the crocodile management team was 5m.
See the map of crocodile captures.
More crocodiles in the NT
There is estimated to be around 100,000 saltwater crocodiles in the wild in the NT.
There are more saltwater crocodiles in the NT than Queensland and Western Australia (WA).
A large proportion of the coastal region of the NT is an ideal habitat for saltwater crocodiles, particularly the big, productive coastal wetlands and rivers.
Queensland crocodile population
Much of the Queensland coastline is in the cooler, more southerly latitudes, which is a less than optimal habitat for crocodiles.
The effect of a cooler climate on crocodiles can be seen in those animals kept in wildlife parks in southern Queensland. The crocodiles do not feed over winter as they cannot absorb enough warmth to digest food.
Much of the habitat on Queensland's east coast has also been significantly altered and fragmented by human settlement making it less than ideal for saltwater crocodiles.
Western Australia crocodile population
WA has some areas of saltwater crocodile habitat around the Kimberley coastline but this area is not as rich in mangroves and wetlands as the NT.
In the southern part of the Kimberley range, winter temperatures reach a threshold below which crocodile eggs will not hatch and the longer cold periods significantly lower crocodile growth rates.
Crocodiles are not culled in the NT
Crocodiles are able to blend into their surroundings and move over extremely large distances on land and water.
This means that culling will never guarantee that any area within the likely range of the saltwater crocodile is ‘crocodile-free’.
Removing one crocodile may simply create more space for the other crocodiles that already live there or allow new crocodiles to move into the newly vacated area.
As the key predator, saltwater crocodiles are a critical part of aquatic ecosystems. If crocodiles are removed from these systems, the functioning of these systems will change considerably.
Crocodiles are also protected under NT, Australian and international laws.
Crocodiles have cultural and social significance to Aboriginal and Torres Strait Islander peoples.
Saltwater crocodile farming and tourism are valuable additions to the NT economy.
They are of considerable scientific and human interest.
Last updated: 10 October 2017