Saltwater crocodile

Saltwater crocodiles are enormous reptiles that are greatly feared because they have been known to eat humans. Their scientific name Crocodylus porosus is Greek, meaning "pebble worm" and "full of callosities." This name describes the appearance of saltwater crocodiles. Their common name comes from their saltwater habitat, but they are also known as estuarine crocodiles. Strangely enough, they not only have a high tolerance for salinity, but can also live in freshwater. "Salties" are probably the most dangerous of all crocodiles, but learning about them can increase awareness and safety.

Anatomy
Saltwater crocodiles are the largest reptiles on earth, both in mass and length. Males are longer and heavier than females, reaching up to 20 ft, with rare reports of ones reaching 23 ft. The typical male will be around 17 ft (5 m) and weigh between 400-500 kg. The smaller females are around 8-10 ft (2.5-3 m) and weigh about 200-300 kg. These estuarine crocodiles have large heads and jaws, containing 64-68 teeth. A pair of ridges run along the snout from the eyes, becoming more prominent with age. Saltwater crocodile scales are oval shaped, except under the belly, where they are small and rectangular. Estuarine crocodiles have four-chambered hearts and a double-loop circulatory system.(Miller & Levine pg 800) Their hind feet are webbed to assist in swimming, and they also have clear eyelids allowing them to see underwater. 

Juveniles are pale or tan in color with black spots and stripes on the tail and body. Some juveniles are lighter in color or even darker, but these are few and rare. As they mature, they grow even paler, their markings growing indistinct. Once they are adults, saltwater crocodiles are usually dark, having only grey or light tan areas. Dark stripes or bands also appear on the flanks. The ventral region tends to be white or creamy yellow, with the exception of the tail which appears grey near the tip.

Reproduction
Saltwater crocodiles reproduce by internal fertilization. Males reach sexual maturity around 16 years of age, while the females are sexually mature at 10-12 years. Breeding takes place in freshwater regions, such as creeks and tidal rivers, during the wet season (November to March). Females build elevated nests out of mud and plant matter, usually laying between 40-60 eggs. The raised nest protects the eggs from predators, insulates them, keeps them from dehydrating, and most importantly, keeps them above the floods. Flooding is the main cause of the destruction of saltwater crocodile eggs. Each egg weighs around 113 grams and is 8 x 5 cm. Several hours after it's laid, the embryo attaches to the shell, creating a white spot on the eggshell. This spot will expand to encompass the whole shell as the embryo grows.

The mother guards her nest for 80 to 90 days until the eggs hatch. The newborn hatchlings make a "chirping" call that alerts the mother. The female then digs her young out of the nest and carries them in her mouth to water. The hatchlings are about 29 cm long and weigh around 72 grams. An interesting fact is that the egg's temperature determines the embryo's gender. If the egg is kept at 31.6 degrees Celsius, a male will be born. Any variation in temperature will usually result in a female. Less than 1% of saltwater crocodiles in the wild survive to adulthood, and at least 80% of eggs die during incubation. 

Ecology
Saltwater crocodiles are distributed over a wide area. They can be found on the coasts of northern Australia, Sri Lanka, Vietnam, the Philippines, and the Solomon Islands. Because they are strong swimmers, saltwater crocodiles have been found as far as 1,000 km out at sea. Estuarine crocodiles have a high tolerance for saltwater, but can also be found in freshwater. They tend to live in brackish water or rivers, and also live in freshwater billabongs, rivers, and swamps. 

Saltwater crocodiles live in loose social groups dominated by the strongest male. Disputes over territory are usually settled by vocalization and body posture rather than violence. Adult crocodiles have few predators besides poachers. Juveniles are prey for a variety of larger animals, including adult crocodiles. Their carnivorous diets as adults consist of reptiles, birds, amphibians, small mammals, and fish. If a saltwater crocodile is especially large they will eat almost anything, including dingos, wallabies, other crocodiles, domestic animals, cattle, large reptiles, carrion, and even humans. Juveniles are restricted to insects, crustaceans, arthropods, and small fish.  Saltwater crocodiles are known as ectotherms (an animal that relies on interactions with the environment to help it control body temperature), so much of their time is spent thermoregulating their internal temperature. (Miller & Levine pg 800) They work to maintain a body temperature between 30-32 degrees Celsius. In an effort to regulate body temperature, estuarine crocodiles submerge themselves almost completely in water to stay cool. To warm up, they bask in the sun on large, flat rocks or sand. 

Conservation
Saltwater crocodiles aren't considered a critically endangered species, but aren't stable either. It is estimated that there are 200,000 to 300,000 saltwater crocodiles in the wild, but illegal poaching, loss of habitat, and a poor reputation with the public leave their future uncertain. The U.S. Fish and Wildlife Service rates the populations of estuarine crocodiles in Australia as "Threatened," but in the rest of their habitat they are considered "Endangered." Since 1999, there have been only two sightings of saltwater crocodiles in Sri Lanka and Thailand. In Vietnam, there is an estimated population of only 100 left in the wild. One of the biggest problems threatening saltwater crocodiles is illegal hunting. Crocodile skins are very valuable, and the saltwater crocodile's is one of the most valued hides for leather products. This has led to the creation of crocodile farms to protect those in the wild. 

Saltwater crocodiles are considered man-eaters because of occasional human deaths. This makes it difficult to get public support in their favor. Fatalities connected with crocodiles are very rare, only 7 occurring in the Northern Territory and 14 in all of Australia during 27 years of protection. These usually occurred when the person was swimming. Additional education and awareness concerning saltwater crocodiles can reduce mortality rates further.