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Ocean Life: Green Sea Turtle - Adaptation

Reproduction

Although Green Sea Turtles live most of their life in the ocean, adult females must return to land to lay their eggs. Upon sexual maturity, the Green Sea Turtle makes an amazing journey every two or three years to nest. They leave their feeding grounds and migrate as far as 800 miles to their nesting beaches. Biologists believe that nesting female turtles return to the same beach where they were born. This beach is called a natal beach. Males do not accompany the females, but they congregate at the breeding grounds. The males will mate with the females off the shores of the nesting beaches. The most popular nesting beaches are on French Frigate Shoals, where 90% of the Hawaiian population of Green Sea Turtles mate and lay their eggs.

Green sea turtles on beach.
Green Sea Turtles
(courtesy of Kathy Streeter, New England Aquarium)

Green Sea Turtles nest only at night. After 7-10 weeks gestation period, the females pull themselves out of the water to the dry sand of the upper beach. Here, she uses her front flippers to dig a broad pit and her rear flippers to excavate an egg chamber. She then lays her clutch, which consists of 100-120 ping-pong sized, leathery-skinned eggs, in the egg chamber and carefully covers them with sand. Females lay up to five or six clutches of eggs in a breeding season. Once she buries the pit and disguises the location, her parenting job is complete. She returns to sea leaving her young to fend for themselves.

Hatching occurs at night and begins in July after about 60 days of incubation. Studies indicate that the temperature of the eggs during incubation influences the sex of the baby sea turtles. At 82 degrees F, hatchlings are male. At 90 degrees F, hatchlings are female. Baby sea turtles are able to chip through the eggshell with a structure called an egg tooth, a temporary hard protuberance on their beaks. Working as a group, the hatchlings dig to the surface of the nest and instantly head to the water, attracted to the moon's light reflecting on the ocean's surface. Therefore, artifical lights on nesting beaches can confuse the hatchlings and cause them to lose their way. Sharks, reef fish, birds and mammals all pose predator threats upon hatchlings. Once they reach the ocean, the hatchlings remain at sea until they appear as juveniles in the near-shore waters. Only 1 or 2 out of 100 hatchlings will survive the first year.

Predators

With their efficient mobility in the water and their size, adult Green Sea Turtles have only two known predators: sharks and man. Tiger sharks feed regularly on Green Sea Turtles. Man has been the greatest predator of the sea turtle, killing it for its meat, shell, and eggs while driving it almost to extinction.

Other Threats

There are many threats to Green Sea Turtles beyond that of predators. Entanglement in commercial shrimp nets trap and drown more than 10,000 sea turtles each year. Litter and other marine debris can be deadly when they entangle the turtles or are mistaken for food and ingested. Nesting grounds are lost each year to coastal development, leaving females without a familiar place to lay their eggs. Noise, lights and beach obstructions disrupt nesting areas and threaten this critical part of the sea turtle's life cycle. The recent presence of a disease called fibropapilloma has affected Green Sea Turtle populations in Hawaii as well as Florida. Fibropapilloma causes the growth of large tumors on the soft tissue of the turtles. The exact cause of the disease is not known. Scientist suspect that a virus, parasite or the effect of marine pollution may be involved.

 

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