A green sea turtle comes up to breathe on sunrise. Like other marine reptiles the green sea turtle must return to the surface to breathe. They are extremely good at holding their breath to prolong time underwater and while resting these turtles have been shown to dive for 7 hours without breathing.  They have the ability to do this by lowering their heart rate to an incredible 1 beat per 9 minutes... Talk about max cruisers.  Foraging or undertaking activities exerting more energy, like trying to escape a hungry tiger shark, this breathe holding ability is significantly reduced as these activities rise the turtles heartrate.