Today scientists recognise seven species of sea turtles, which developed from a single, unique group that separated from other turtle species over 100 million years ago. This group then split into two families, Cheloniidae and Dermochelyidae.
The cheloniidae include six of the existing species: loggerhead (Caretta caretta), green (Chelonia mydas), hawksbill (Eretmochelys imbricata), olive ridley (Lepidochelys olivacea), Kemp’s ridley (Lepidochelys kempii) and flatback (Natator depressus). Dermochelyidae is represented solely by the leatherback turtle (Dermochelys coriacea), which lacks the hard shell that characterizes other marine turtles. Of these seven species, only 3 still nest on the beach of Campamento Majahuas: olive ridley, black turtle (also known as Pacific green turtle, Chelonia mydas agassizi) and leatherback.
The most common species nesting at Majahuas is the olive ridley, historically known for its ‘arribadas’. This is a mass nesting phenomenon, where thousands of turtles come to shore to nest over a short period. The occurrence of these arribadas however, had declined considerably by the 1980’s due to over exploitation of sea turtle populations by their main predators, humans. Today there is only one beach left on Mexico’s Pacific coast where these arribadas take place. Although many olive ridley populations have responded well to conservation efforts and are now stable or increasing in numbers, it is important to continue with such efforts in order to ensure that a repeat of past declines is prevented.