Crocodiles

The Queensland Crocodile Management Plan is the overarching framework for the statewide management of public safety risks associated with crocodiles in Queensland. For more information, including a copy of the plan and associated zone maps, see conservation and management.

A great survivor

Crocodiles have reigned as key predators in wetland and marine environments for millions of years. Differing little from their prehistoric ancestors that stalked the earth before the dinosaurs, crocodiles have survived major upheavals, such as the break-up of the world's continents and the ice ages.

Today, crocodiles are one of the few remaining links to the prehistoric past. As predator and prey, crocodiles play a valuable role in the health of many aquatic environments.

Croc country

Australia is fortunate to be home to two species of crocodile, the freshwater crocodile (Crocodylus johnstoni), which is found nowhere else in the world, and the vulnerable estuarine crocodile (Crocodylus porosus). In spite of their common names, both species can live in fresh or salt water.

The freshwater crocodile lives 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. There are also east coast populations found 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 from India, throughout south-east Asia and New Guinea, across to northern Australia, Vanuatu and the Solomon Islands. In Queensland, they are known to occur between Gladstone and Cape York Peninsula, and throughout the Gulf of Carpentaria. Although most commonly seen in tidal reaches of rivers, they also occur 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.

Flooding and potentially dangerous wildlife

Flooding of waterways and low-lying areas can temporarily increase the mobility and distribution of potentially dangerous wildlife—including crocodiles—and as such crocodiles may be present in areas they do not usually inhabit.

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 are unable to 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 locomotion, and ultimately for their survival.

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. Although livelier in the water, crocodiles are able to swim just below the surface, with only their eyes and nostrils visible.

Crocodiles are one of the few reptiles to have a four-chambered heart (like mammals). They can also stay underwater for extended periods of time because they have the ability to slow their heart rate, allowing them to hold their breath.

A unique feature of crocodiles is their inability to maintain strenuous activity for extended periods of time. They can easily become exhausted while capturing prey or fighting other crocodiles. Extreme exertion is carried out 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.

Never trust a crocodile smile

A crocodile has a constant supply of new teeth. Each time an old tooth falls out a new one will replace it.

Snapping crocodiles

Crocodiles have very strong muscles used to close their jaws, which can easily crush a pig's skull—but a sturdy rubber band around the snout of a 2-metre estuarine crocodile is enough to keep it from using its comparatively weaker "opening" muscles.

It's a slow-ticking clock for crocs

Crocodiles have growing spurts during the hot wet months. This creates distinct growth rings in the crocodiles' bones that can be used to estimate their ages. Based on an analysis of growth rings, one adult male freshwater crocodile was estimated to be about 70 years old, so it is possible that they could reach 100 years of age.

Salt environment no problem for estuarine crocodiles

Estuarine crocodiles are unique in the reptile world in that they use their blood system to remove salt from their body. Salt glands embedded in their tongue tissue excrete excess salt when the animal is living in a highly saline environment.

Communicating with crocodiles

Crocodiles use physical displays, chemical and vocal signals to communicate. They have no vocal chords so forcing air from their lungs through the back of the throat or nostrils is how they make their vocal noises.

Food for thought

Crocodiles are large and skillful predators that hunt by stealth. Their muscular tail propels them through the 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 are able to see underwater due to a transparent lid that closes over their eye for protection. They also have excellent night vision, thanks to a specialised retina, as well as a keen 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 feed on 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 items are too big to swallow whole, the crocodile may roll several times or shake its head in an attempt to break off a more manageable 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 are able to 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

The relationship between crocodiles and humans has been a long and interesting one. 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 David Fleay Wildlife Park on the Gold Coast.

Vulnerable to extinction

Until 1974, estuarine crocodiles in Queensland were hunted to the brink of extinction for their prized skins. Both species are now protected throughout Australia, but other pressures continue to threaten these animals.

It is estimated that less than one percent of eggs laid by estuarine crocodiles hatch and survive to adulthood. Overheating, flooding and predation by goannas and feral pigs claim a high proportion of unhatched embryos (an estimated 70–80 percent). 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 have reached 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 in on crocodile territory—developments in swamps, mangroves and rivers are displacing crocodiles from their homes.

Management and research

The department must meet the challenge of protecting crocodiles and preventing their extinction, while trying to ensure that people can safely co-exist with these animals.

While thousands of crocodiles are killed in other countries for their skins, Australia's two 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 from the department.

The ‘Crocwise’ Education Campaign, in operation since October 2001, was developed by the department to inform the public about the value of crocodiles and their habitat. It also provides information about the importance and dangers of crocodiles through various interpretive strategies. These include:

• media announcements
• educational posters and brochures
• talkback radio
• warning signs
• ranger talks
• displays
• stickers
• magazine articles
• websites such as this one.

The department is concerned about crocodile and human interactions. The Queensland Crocodile Management Plan is the overarching framework for the statewide management of public safety risks associated with crocodiles in Queensland.

The department carries out research on wild populations of crocodiles. Through research, it hopes to:

• assess crocodile numbers, distribution and movement patterns
• gain a better understanding of their population dynamics
• gain a better understanding of their reproductive biology
• encourage conservation and management of healthy wild populations, while keeping the risk to people as low as possible.

This information assists in the continual improvement of management practices.

You can help with this research by reporting crocodile sightings to your local departmental office.

Crocodile alert

Throughout north and central Queensland, yellow warning signs are placed at access points to waterways where estuarine crocodiles might live. Be aware, estuarine crocodiles may be present, even if there are no warning signs. If in doubt, obtain advice from the department.

Although there have been recorded estuarine crocodile attacks on humans, statistics show that you are more likely to die from a lightning strike or bee sting than from a crocodile attack. But remember, be Crocwise in croc country!

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 vitally important. This means Australians have a responsibility to conserve and manage the country's crocodile populations carefully.

When visiting crocodile habitats, take care. Respect these animals and appreciate that, like other native animals, crocodiles are part of the natural and cultural heritage of northern Australia.

Follow these simple guidelines to help protect crocodiles:

• never interfere with crocodiles or their eggs
• report any incidents of crocodile killing or poaching to the nearest departmental office
• be Crocwise in croc country.

Further information

For further information about crocodiles contact us or to report sightings please phone 1300 130 372 or visit CrocWatch.

Grigg, G. and Kirshner, D. (2015). “Biology and Evolution of Crocodylians” 649 Pp. CSIRO Publishing, Clayton, Victoria; Cornell University Press, New York.

Webb, G. and Manolis, C. (1989). Australian Crocodiles. A Natural History. Reed Books.