Swimming with Sea Turtles while Scuba Diving
Turtles, sea snakes, one kind of lizard, and a crocodile make up the marine reptiles. By far, the most commonly encountered by scuba divers are the marine turtles, although six of the seven species of marine turtles in the world today are threatened or endangered — entirely due to the activities of humankind.
Marine turtles are well adapted to life in the sea compared to their terrestrial relations — their shells, or carapace (CARE-a-pace), are flattened and streamlined, and their legs have evolved into flippers and paddles. In spite of their adaptations, they must still return to the surface to breathe and to land to lay eggs.
Destruction of their breeding habitat is one of the principal reasons that turtle populations are threatened worldwide. All species of sea turtles are protected under international treaty, and all six of the sea turtles that occur in United States territorial waters are protected under the Endangered Species Act. But their recovery is slow and still very much in doubt.
The seven species, shown in Figure 1, are as follows:
- Green: Green sea turtles are 3 to 4 feet in length and between 200 and 300 pounds. Their carapace is oval-shaped with mottled gray, brown, and cream-colored markings. Greens are probably the most commonly sighted by divers. They frequent shallow coastal waters where they feed mostly on algae and seagrasses.
- Hawksbill: Hawksbills are a little smaller than greens — about 3 feet long and generally between 100 and 200 pounds. Hawksbills have a beautiful, mottled carapace for which they were, and still are, hunted. Hawksbills can be recognized by their distinctive hooked beak and the jagged edge on the tail-end of their carapace. They are often sighted on the reef feeding on sponges, tunicates, and shrimp.
- Loggerhead: Adult loggerhead turtles are normally 3 to 4 feet in length and weigh between 200 and 400 pounds. Their carapace is oval and often has a reddish-brown tint. Loggerheads are commonly encountered in the coastal waters of the southeastern United States and in the Caribbean. They can be identified by their large heads and powerful jaws, which are designed for crushing and grinding the crustaceans and mollusks on which they feed.
- Kemp's ridley: Kemp's ridley is the smallest and most endangered of all the sea turtles. They are seldom larger than 30 inches, and usually between 80 and 100 pounds. This species has a rounded carapace that is normally olive-gray. They are found only in the coastal waters and bays of the northern Gulf of Mexico, where they forage for crabs.
- At a single nesting site in Mexico, 40,000 female Kemp's ridleys came ashore to nest in 1947. Today, less than 500 nest on the same beach. They are very rare and a diver is unlikely to see one.
- Olive ridley: The Olive ridley is similar to Kemp's ridley, except that their carapace is more highly domed and has more variation. There also are some other differences that no one but an expert can detect. Olive ridley's are also very rare and it is unlikely you will see one in the wild, at least for the foreseeable future, although recovery programs are in progress.
- Leatherback: These are the giants of the sea turtle clan. Specimens of leatherbacks have reached 6 feet in length and weigh as much as 1,400 pounds. Unlike other species, the leatherback does not have a hard carapace but a smooth, dark, leathery hide with seven longitudinal ridges. Leatherbacks are a highly migratory species and are often seen in open water. They feed primarily on jellyfish.
- Flatback: The flatback turtle is found primarily in the coastal waters of northern Australia — they are sometimes seen as far north as Indonesia and Papua New Guinea, but all of their known nesting sites are in northern Australia. The flatback's carapace is olive-gray and oval-shaped with a flattened dome from which they take their name.
- Flatbacks average about 3 feet in length and weigh 200 to 300 pounds. They are normally found in shallow coastal waters between the Great Barrier Reef and the Queensland shore, out hunting for sea cucumbers, soft corals, jellyfish, and other soft-bodied marine species.