It is possible to go on a Hawaii scuba diving tour and experience sea turtles up close. Four species of sea turtles can be found in Hawaiian waters. They are the Hawksbill, Leatherback, Olive Ridley, and Green Sea Turtle. The green sea turtle is the most common turtle you will see on a Hawaii scuba dive. Hawaii's green sea turtles are herbivores, feeding mostly on algae. Green sea turtles can live as long as 80 years and weigh 350 pounds or more. Green sea turtles are the worlds largest hardshell sea turtle. Sea turtles are air breathing swimming turtles that can stay underwater for more than two hours while sleeping. Green sea turtles have flipper feet and can surprisingly swim well, but even in the ocean world turtles need the protection of their shells. Unlike most turtles, green sea turtles cannot retract their head into their shell. Because of their tuff shell, green sea turtles only have two predators sharks and humans. While the days of man hunting green sea turtles in Hawaii is over, there is still concern over degradation of their feeding habitat. Green sea turtle females are believed to return to the same beach they were born at to nest. Hawaii sea turtle nesting sites are protected by the U.S. Fish and Wildlife Service's National Wildlife Refuge System.