Saltwater Crocodile

The Basics

The saltwater crocodile is a species of reptile found in brackish swamps, rivers and estuaries. Its range extends from eastern India across Southeast Asia to northern Australia and the islands of Micronesia. It is not only the largest of the sixteen extant species of crocodile, but is the largest living reptile on earth. The saltwater crocodile also has the greatest distribution and is the most aggressive of all extant crocodile species.

Juvenile saltwater crocodiles are pale yellow with black spots and stripes on their bodies and tails. This coloration persists for several years until these animals reach maturity. Adults tend to be a darker green color, although several variants exist ranging from relatively pale to almost black. Similar to juveniles, adult saltwater crocodiles also have dark spots on their bodies and dark bands on their tails, whilst their undersides are white or yellow.

Hunting

The saltwater crocodile is the apex predator across its range and will eat almost any animal available, including other traditional apex predators such as the shark. Saltwater crocodiles are ambush predators and quietly approach their prey whilst submerged underwater before suddenly pouncing out of the water to attack. Although certain crocodile species such as the Nile crocodile sometimes hunt on land, the saltwater crocodile is not known to do so.

As is the case for all crocodiles, the sharp, peg-like teeth of saltwater crocodiles are well-adapted for tightly gripping prey, but not for tearing flesh. Therefore, small prey animals are simply swallowed whole, whilst larger animals are dragged into deep water and drowned or crushed. Saltwater crocodiles then tear off manageable pieces of meat via sudden jerks of the head or use a technique called ‘death-rolling’, in which the crocodile spins repeatedly to twist off chunks of meat.

Saltwater crocodiles are very lethargic and use little energy throughout the day, so can survive for months at a time without food. These animals prefer to hunt at night and spend most of the day inactive in the water or basking in the sun on land. Saltwater crocodiles generally spend less time on land than other crocodile species, however, often being at sea for weeks at a time. Whilst at sea, these crocodiles use ocean currents to travel huge distances with little energy expenditure and can travel as far as 370 miles (590 km) in 25 days.

Reproduction

Saltwater crocodiles mate in the wet season and it is possible that reproductive behavior in this species is brought on by rising temperatures during this season. Females typically lay 40 – 60 eggs, although clutches can contain as many as 90 eggs. Nests are placed on shorelines and consist of mounds of mud and vegetation measuring around 5.8 feet (175 cm) wide and 1.8 feet (53 cm) high with a central cavity in which the eggs are deposited. Once all eggs have been laid, the female covers over the entrance to the nest using leaves and other debris.

Females usually guard the nest for 80 to 98 days before the eggs hatch. Juvenile saltwater crocodiles begin to disperse at around 8 months old and start to display territorial behavior at around 2 and a half years old. These animals are the most territorial of all crocodiles and unlike other species are never seen in groups after dispersal age. Male saltwater crocodiles reach sexual maturity at around 16 years of age, whilst females reach sexual maturity at around 12 – 14 years of age.

Fun Facts about Saltwater Crocodiles

The deadly jaws of the saltwater crocodile are one of several interesting traits that demonstrate important biological concepts.

Sex and Temperature

The saltwater crocodile exhibits temperature-dependent sex determination, along with all other crocodilians and many other reptiles including turtles and lizards. This means that the sex of offspring in these groups is determined by egg temperature during incubation, specifically during the middle third of embryonic development. This period is known as the thermosensitive period, after which sex is irreversibly determined. Although the exact mechanism of temperature-dependent sex determination is not fully understood, it is thought that temperature influences the expression of genes involved in the differentiation of the gonads.

The temperatures at which males and females are produced varies between species. For example, males develop below a certain temperature and females develop above this temperature in most turtle species, but the opposite pattern is true in the tuatara. In the saltwater crocodile, eggs at 82 – 86 ^oF (28 – 30 ^oC) will all hatch as female, those at 86 – 90 ^oF (30 – 32 ^oC) will be over 80% male, and those at 91 ^oF (33 ^oC) or above will be over 80% female. This sex determination system makes saltwater crocodiles and other species vulnerable to climate change, as they are unlikely to be able to adapt fast enough to rising temperatures, so will probably exhibit skewed sex ratios in the future, possibly leading to extinction.

Maternal Care

Saltwater crocodiles, like most crocodilians, exhibit high levels of maternal care in comparison to other reptiles. For example, they help excavate the nest in response to the yelping calls of hatchlings and will even roll eggs around in their mouths to aid hatching. Females then carry their young to the water in their mouths and remain with them for several months. Despite this high level of care, only 1% of hatchlings survive to adulthood, with most succumbing to attacks by predators and even other saltwater crocodiles.

Maternal care is essential for the survival of offspring in many classes of vertebrate, but is most prevalent in mammals, since mothers in this group directly feed their young via suckling. In the majority bird species, both mothers and fathers provide care for offspring by provisioning them with food that the flightless hatchlings would not be able to obtain themselves. However, in may reptile species including the saltwater crocodile, hatchlings are able to hunt independently, so do not rely on their parents for food. Instead, saltwater crocodile mothers might remain with their offspring for several months to provide some protection from the plethora of predators that threaten hatchlings.

Bite Strength

Saltwater crocodiles are extremely successful apex predators thanks to their huge bite force, which is the strongest of any living animal. One adaptation that has contributed to the evolution of this animal’s strong bite is the large space for the jaw muscle in the skull. This allows the jaw muscle to grow so large that it can easily be seen as bulges on either side of a saltwater crocodile’s head. As well as this, the jaw muscle fibres of saltwater crocodiles are arranged in a way that maximises their ability to clamp down. In contrast, these animals have very small and weak muscles for opening the jaw because the majority of resources have been directed towards strengthening their deadly bite.