Australia is home to 2 species of crocodile, the freshwater crocodile (Crocodylus johnstoni), which is found nowhere else in the world, and the estuarine crocodile (Crocodylus porosus). Both species can live in fresh or salt water.
Freshwater crocodiles live in the inland waterways of northern Australia. In Queensland, they are found in the rivers and swamps of Cape York Peninsula, areas bordering the Gulf of Carpentaria and the north-west. East coast populations exist in the upper Herbert River, the Burdekin River catchment and the Ross River. Freshwater crocodiles also live in tidal reaches of some rivers.
Estuarine crocodiles are found in India, throughout South-East Asia and New Guinea, in northern Australia, Vanuatu and the Solomon Islands. In Queensland, they are known to live between Gladstone and Cape York Peninsula, and throughout the Gulf of Carpentaria. Although most commonly seen in tidal reaches of rivers, they also live in freshwater lagoons, rivers, and swamps hundreds of kilometres inland from the coast. They can even be found along beaches and around offshore islands in the Great Barrier Reef and Torres Strait.
The life of a crocodile
Crocodiles use the water, sun and shade to maintain their preferred body temperature of 30–33°C. When basking, they orientate their bodies to ensure the maximum surface area is exposed to the sun. Crocodiles cannot sweat. To avoid over-heating they may return to the water or lie with their jaws agape, allowing cool air to circulate over the skin in their mouths. This process of heating and cooling their bodies is called thermoregulation and is crucial for many bodily functions including digestion and movement.
Often observed basking on the banks of watercourses where they are generally inactive, crocodiles are less likely to be seen when they are in the water. Livelier in the water, crocodiles can swim just below the surface, with only their eyes and nostrils visible.
Crocodiles are one of the few reptiles to have a 4-chambered heart (like mammals). They can also stay underwater for extended time because they can slow their heart rate, allowing them to hold their breath for longer.
However, they cannot maintain strenuous activity for long periods and can easily become exhausted while capturing prey or fighting other crocodiles. Extreme exertion is done anaerobically (without oxygen) and must be followed by a period of rest so that the ‘oxygen debt’ can be repaid to their muscles. The result of anaerobic activity is a build-up of lactic acid in the blood. Although crocodiles can withstand higher levels of blood acidity than other animals, sometimes it can be fatal.
Crocodiles are large and skilful predators that hunt by stealth. Their muscular tail propels them through water and allows them to lunge forward with great power and speed. It can also be used to thrust them vertically to capture a bat or bird in mid-flight or in foliage.
Crocodiles can see underwater due to a transparent lid that closes over their eye to protect it. They also have excellent night vision, due to a specialised retina, as well as a good sense of smell. Small sensory buds around the top and bottom jaws allow crocodiles to detect vibrations—crucial when hunting in murky water.
Crocodiles are opportunistic feeders that eat a variety of animals. Their jaws have immense crushing power, enabling them to easily break through skulls and other bones. Prey is not chewed but swallowed as large chunks. If the chunks are too big to swallow whole, the crocodile may roll several times or shake its head in an attempt to break off a smaller piece. Although their stomach secretions are highly acidic, they cannot digest some items, such as fur, hooves and turtle shells. These items collect in the stomach and may either be passed through undigested or turned into ‘hairballs’ and regurgitated later.
Studies have shown that crocodiles can convert as much as 50–70% of their food into growth and energy. By contrast, humans use only 3–4%—up to 80% of our food is used to produce heat and maintain a constant body temperature. This efficiency in crocodiles means that they can go for months without eating.
People and crocodiles
Traditionally, Aboriginal and Torres Strait Islander peoples have had a special relationship with crocodiles. They are the focus of stories, songs, dances and art. Some groups regard crocodiles as religious icons or totems, while others believe they are spirits of ancestors. Crocodiles are also a food source for some traditional groups who take eggs from nests and hunt adults.
Commercially, crocodiles are now an important resource. Farmed crocodile meat is a gourmet item on many menus around the world, and their skins are recognised as a durable leather that is made into a variety of products. Crocodiles are also a major tourist attraction throughout northern Australia, both in the wild and in wildlife sanctuaries. You can see both species of crocodiles at the David Fleay Wildlife Park on the Gold Coast.
Vulnerable to extinction
Until 1974, estuarine crocodiles in Queensland were hunted close to extinction for their prized skins. Both species are now protected in Australia, but their numbers continue to be threatened.
It is estimated that less than 1% of eggs laid by estuarine crocodiles hatch and survive to adulthood. Overheating, flooding and predation by goannas and feral pigs claim an estimated 70–80% of unhatched embryos. From the small numbers that do hatch, more than half die in their first year of life, mainly from predation by birds of prey, fish, snake-necked turtles and other crocodiles. Once they reach maturity their only enemies are each other and humans.
Habitat destruction is now considered a major threat to crocodile survival in Queensland. Increasingly, humans are crowding crocodile territory—developments in swamps, mangroves and rivers are displacing crocodiles from their homes.
The growing human population along the east coast of Queensland ultimately means more frequent encounters with crocodiles. Unless the community values crocodiles and their habitats, it will be a challenge to ensure their long-term conservation.
Management and research
We are working to meet the challenge of protecting crocodiles and preventing their extinction, while trying to ensure that people can safely coexist with these animals.
While thousands of crocodiles are killed in other countries for their skins, Australia's 2 crocodile species are protected in the wild. This means that it is illegal to interfere with these animals, which includes removing eggs, and possessing or taking crocodile parts (such as skulls and skins) without a licence.
Dangerous crocodiles in populated areas are investigated and those that are deemed to be a threat to people, dogs or stock are captured and removed. These crocodiles are then made available to commercial crocodile farms and zoos. Destroying a wild crocodile is the last resort.
Through research on wild crocodiles, we hope to:
- assess crocodile numbers, distribution and movement patterns
- gain a better understanding of their population dynamics and reproductive biology
- encourage conservation and management of healthy wild populations, while keeping the risk to people as low as possible.
Our research findings help us improve how we manage crocodiles.
Contact us if you see a crocodile and help with our research.
In North and Central Queensland, yellow warning signs are placed at access points to waterways where estuarine crocodiles may live. Be aware, estuarine crocodiles may be present, even if there are no warning signs.
Although estuarine crocodile attacks on humans are recorded, statistics show that you are more likely to die from a lightning strike or bee sting than from a crocodile attack.
But remember, be croc wise.
The future for crocodiles
Australia is one of the very few places in the world where estuarine crocodiles have a good chance of survival in the wild, and the only country where the freshwater crocodile is found. Because crocodiles are an important part of the food chain and help keep our wetland environments healthy and stable, protecting them is critical. This means you have a responsibility to conserve and manage our crocodile populations.
When visiting crocodile habitats, take care, respect these animals and appreciate that crocodiles are part of the natural and cultural heritage of northern Australia.
Follow these simple guidelines: