The green sea turtle, also known as the green turtle, black (sea) turtle or Pacific green turtle. They are very highly protected animals in Hawaii. It is illegal to kill, capture, touch or harass sea turtles. Fines can be as high as $25,000 and may include a year in prison.
On the Oahu island the Makaha Beach is one of the best spot to see them if you have snorkeling gear and if you are a strong swimmer you could swim out to the sea and see several of them easily.
I took this picture btw :)