Include some of the most charismatic marine vertebrates and some of the most deadly. There are not many of these relatives of the dinosaurs in the seas—seven species of turtles, 54 species of sea snake, the one salt-water crocodile, and the one marine iguana.
The most charismatic of marine reptiles, these are gentle giants. They are under threat because they come ashore to lay their eggs on sandy tropical beaches that are ideal for tourist development. Their eggs, while they are incubating in the hot sand, are plundered by a variety of predators. Those hatchlings that survive have to run the gamut of seabirds and sea mammals as they scuttle across the beaches to the relative safety of the water, but even there they are gobbled up by hungry fish and sharks. Once safely at sea they roam the oceans feeding on gelatinous animals like jellyfish drifting with the ocean currents.
There are two families of sea turtles, the Dermochelyidae (leatherback) and the Cheloniidae (loggerhead, green turtle, ridley, and hawksbill). Leatherbacks (Dermochelys coriacea), the world's most endangered sea turtle, have been on earth 100 million years, 25 times longer than man, and can measure up to 2.1 metres (7 ft) in length and weigh well over 500 kilograms (1,000 lb). They are often the victims of long-lining and fishermen's nets, and their numbers have declined disastrously during the last two decades. However, their extinction is not a foregone conclusion as international cooperation has reversed the decline of another species, Kemp's ridleys (Lepidochelys kempii), from 300 nesting females counted in the 1980s to the 6,200 counted in 2002. Leatherbacks regularly occur off the coasts of Britain, enticed there by the vast swarms of gelatinous animals called salps that appear there in early summer. Hawksbill turtles (Caretta caretta) will eat Portuguese men-of-war. However, many are killed when their stomachs become clogged with discarded plastic bags (see also pollution), which they mistake for gelatinous animals.
occur mostly in tropical waters of the Indo-Pacific. Most species come ashore to lay eggs, but a few give birth to live young in the water. Being air-breathers, they have to keep close to the surface. Their tails are flattened laterally, making them more efficient at swimming. They feed on fish, killing them by biting with highly venomous fangs. Their bites are lethal to humans, but being back-fanged they have difficulty biting us. Around Australia, the common yellow-bellied sea snake (Pelamis platurus) occasionally gets stranded in large numbers on beaches.
Salt-water crocodiles are more dangerous than sea snakes, They inhabit the tropical estuaries of South-East Asia and northern Australia and can grow to huge sizes. Despite being protected they are heavily persecuted.
The marine iguana (Amblyrhynchus cristatus) is one of a range of reptiles unique to the Galapagos archipelago. They browse on the seaweeds that grow on the larva rocks along the coasts. They are not great swimmers and, as noted by Charles Darwin, the population on each island is subtly different, suggesting that each population is beginning to diverge and evolve into a separate species.
Subjects: Maritime History.