The sea turtles are an easily recognised and well known group of marine reptiles. Although found in all the oceans of the world, they are basically a tropical group and are most common in the warm seas around the equator. They reach large body sizes, are surprisingly fast swimmers and feed on a wide variety of marine animals and plants. Today all species are experiencing serious threats to their survival due to the over-harvesting by humans of adult turtles and their eggs.

• A body covered in bony plates or leathery shields, with those on the back fused to the vertebrae and ribs.
• No teeth, but a horny parrot-like beak with a cutting edge.
• Limbs that are paddle-shaped. No webbing or clawed feet allowed.
• To come ashore only to lay eggs.
• Salt glands located behind the eye which excretes excess salt as briny tears.

Sometimes incorrectly called tortoises.

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.

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.

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.

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.

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.

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.