Crocodiles

What do they look like?
All crocodiles have an instantly recognisable lizard-like body shape, with four legs and a toothy smile. This smile is because the large teeth at the front of the lower jaw fit into notches at the side of the upper jaw, and are visible even when the mouth is closed. The muscular tail is vertically flattened, and like a paddle, provides more surface area for rapid swimming, while the four webbed toes on the back feet are used only for slow, precise movement under water. On land all four feet are used and the body is held high off the ground while walking, in a comical, swaying motion. The thick scales on the back overlay bony plates inside for added strength. The eyes are set high on the head, and, together with the valved nostrils, are often the only visible evidence that a giant prehistoric reptile lies beneath the water.

Where do they live?
Saltwater and American crocodiles live in either freshwater, estuarine or sea water. The saltwater crocodile occurs across South East Asia to New Guinea, the Solomon Islands and tropical Australian waters, and the American crocodile is found from Florida in the USA, south through the Caribbean islands and along the Central American coast to Ecuador and Colombia. All crocodiles are restricted to warm waters, and unlike alligators, will not survive in areas where water temperatures drop much below 25oC. Only adults are likely to be found at sea or living on reefs, as juveniles prefer estuaries or rivers.

How and what do they eat?
All crocodiles are unashamed carnivores. Hatchlings will eat crabs, mud skippers, frogs, small fish and even insects caught in or out of the water. As they grow larger they include prey such as water birds, mammals, turtles and larger fish in their diet. They hunt by slowly approaching an unsuspecting animal, and when they get within reach they make a powerful and lightning fast side-ways snap with the open jaws. If the captured prey is large or struggling, the crocodile will roll over and over rapidly while holding tight with its jaws. This has the effect of ripping and smashing up the prey, thus killing it and breaking it into pieces for easy swallowing. The struggling prey may also be held underwater until it drowns. The teeth are conical and sharp tipped, but without a cutting edge. Feeding will occur either by day or night, as crocodiles have excellent night vision.

What eats them?
Small crocodiles are eaten by predatory birds, some large lizards and snakes, fish and other crocodiles. As they grow the tables are turned, and many of these predators in turn become the crocodiles food. By the time they reach maturity they have outgrown all their predators except other, larger crocodiles and man. As large male crocodiles are highly territorial they will sometimes kill and eat smaller trespassing males and small adults in their territory

How do they grow and reproduce?
Crocodile eggs have a calcareous "chicken-egg" like shell, and up to 80 are laid in the central chamber of a carefully constructed nests that is guarded by the mother. The saltwater crocodile scrapes up a large mound of grass, other plant material and soil, and deposits the eggs inside, while the American crocodile is more likely to bury her eggs in a hole on an open, sandy beach. The mother will stay close and guard the nest, and on hearing the hatchlings' squawk from inside, will open it and carry them down to the water. Hatchlings hunt and feed for themselves, but usually under the watchful eye of their mother who stays nearby for weeks or even months. The sex of the hatchling is determined by the incubation temperature, and very warm and cool incubation temperatures produce females, while intermediate temperatures of about 32OC produce mainly males.

Their connection with people.
Crocodiles grow large and regard humans as just another tasty food item. In areas where they are still common, people do not swim or bath in open water. However, in most of their former habitat they are rarely seen today as their numbers have been severely diminished by skin hunters. Only in areas of Australia's Northern Territory where they have had legal protection since the 1970s are saltwater crocodile numbers now approaching what they probably were before the 1950s. American crocodiles are endangered in all of their former geographic range. An increasing threat to the survival of these species in some areas is gill netting for fish in estuarine and inshore waters. Many crocodiles become snared and tangled, and subsequently drown in these nets. Notes: In many tropical countries crocodiles are farmed for their excellent skins. The skins are processed and the leather is used for high quality and expensive shoes, handbags and other luxury items, while the meat is in great demand for human consumption. Eggs may be removed from wild nests and hatched in incubators (crocodile ranching - as in the Australian Northern Territory), or alternatively they may be collected from nests constructed by farmed adult crocodiles. If the eggs are hatched in an incubator the crocodile farmer will usually prefer male hatchlings as these grow faster than females. Conveniently for crocodile farmers, the sex of the hatchling is determined by the incubation temperature (see above).

Turtles

What do they look like?
The large and distinctive looking sea turtles (Family Cheloniidae and Dermochelyidae) are in some way similar to their smaller fresh water relatives, but lack webbed feet and always have less than four toes with claws. Instead they have long and powerful paddle-shaped limbs. There are seven species worldwide and six occur in Australian waters. The largest of these, the leatherback turtle, can grow to 2.8 meters in length and weigh over 500 Kg.

Where do they live?
Warm equatorial and tropical ocean waters are preferred by sea turtles, although some species venture far into cooler temperate waters. Most species prefer tropical sub-tidal coral and rocky reefs with relatively shallow bottoms. Their distribution is world wide within the tropics.

How and what do they eat?
Sea turtles eat a wide variety of foods. Some species eat almost exclusively jellyfishes, others mostly sponges, while still other species are more omnivorous and may consume molluscs, crustaceans, fish, urchins and a wide variety of marine algae (seaweed). The adult green turtle eats mostly seaweeds and seagrasses, although the young ones are carnivorous.

What eats them?
A large sea turtle has few enemies except perhaps sharks and humans. However, both the nests and the hatchling turtles have many predators. The nests are often plundered and the eggs eaten by a wide variety of lizards and mammals, including humans. Hatchling sea turtles usually emerge from their nests at night and rush towards the sea. Those that emerge during the day face predatory seabirds on shore, while at night crabs and predatory fish wait in the ocean.

How do they grow and reproduce?
Sea turtles may take from ten to fifty years to reach maturity, depending on the species and the availability of food. Some species migrate thousands of kilometres between their normal feeding grounds and the nesting beaches. Mating takes place in the sea off the nesting beach, and later the females come ashore at night to dig an open pit with the front and back flippers. Within this pit a deep egg chamber is excavated with the long hindflippers, and up to 200 eggs can be laid. After the nest is filled in, sand is scattered over the area to disguise it.

Their connection with people.
Sea turtles and their eggs have been an important source of food for coastal fishing people for thousands of years. However, with the increasing human population all species are now experiencing serious threats to their survival in much of their former range. Recent nests are easily found by following the females distinctive tracks in the sand, and the adult females themselves are easily captured while ashore to nest. Modern fishing techniques are also partly to blame. They are often caught and drowned in seine nets meant for fish and prawns, and many countries now enforce the use of Turtle Exclusion Devices (TEDs) in these types of nets by all professional fisherman. Notes: The names turtle and tortoise are often used interchangeably, and the usage varies from country to country. However, tortoise usually refers to the completely terrestrial members of this order (Testudines), a group that do not occur in Australia.

Snakes

What do they look like?
Sea snakes look basically just like land snakes, but have a flattened tail paddle. Adults vary in size from half a metre to about two metres in total length depending on the species. Some have bizarre adaptations for feeding on specific prey: one species has a long, thin neck and tiny head on a large, thick body. This is an extreme adaptation for reaching the fish eggs that are its sole diet, and which are hidden deep within rock cracks and holes. Colour is very variable in the sea snakes, but a surprising number of species have regular bands or rings of colour around the body, presumably for camouflage, and perhaps to advertise that they are very poisonous or nasty tasting.

Where do they live?
The true sea snakes live in tropical and subtropical oceans from the Persian Gulf across through South East Asia to the Western Pacific and Northern Australia. None are found in the Atlantic Ocean. One species lives in a freshwater lake on Luzon island in the Philippines, while all others are marine. Many species are demersal and live in estuaries, mangroves and on shallow reefs. Only one species, the yellow-bellied sea snake, is truly pelagic and can be found thousands of kilometres from land in both the Indian and Pacific Oceans.

How and what do they eat?
Most species have toxic venom for quickly immobilising the fish, eels and crustaceans that make up their diet. In a few species that are specialised fish egg eaters, the venom and the fangs are degenerate and non functional. Other species have become highly specialised in their diet and only eat a single type of prey, such as eels, gobies or catfish. The most common species encountered in non-tropical areas, the yellow-bellied sea snake, travels along on the surface with floating debris in mid-ocean and eats the small fish that associate with these rafts.

What eats them?
Predators of sea snakes include sea eagles from above, and sharks, large predatory fish, eels, and perhaps even crocodiles from below. The surface dwelling yellow-bellied sea snake is believed to be unpalatable, as there are no reports of sharks, fish or predatory birds eating them.

How do they grow and reproduce?
The true sea snakes are the only truly marine reptiles, reproducing at sea. All other marine reptiles must return to land to breed. Fertilised eggs are retained inside the mothers' oviduct until they are fully developed, and all young are born live (viviparous). The new born young are independent from birth. Little is know about growth rates and survivorship in sea snakes, as little research has been done on this group.

Who do they live with?
Sea snakes are an important component of the fauna on many tropical reefs. They are usually forage on fish or eels, and some species are very abundant on shallow reefs.

Their connection with people.
Sea snakes are rarely seen by most humans, however fishermen in tropical areas are well aware of their toxic venom and treat them with caution. In South East Asia, fishermen are often accidentally bitten by one common species, the Beaked Sea snake (Enhydrina schistosa), while clearing nets and many subsequently die from the effects of its potent venom. The yellow-bellied sea snake is occasionally encountered washed up on shore in temperate areas such as Tasmania and New Zealand. Sea snakes are also common by-catch in the prawn industry in northern Australia, and a preliminary study to investigate the feasibility of a skin industry (for leather) has been undertaken.