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
(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.
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.
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.