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Sea TurtlesGreen Sea Turtle
Green Sea Turtle
Common Name: Green Sea Turtle
Scientific Name: Chelonia mydas
Description
Green
turtles
are the largest of the hard-shelled sea turtles
with adults reaching a meter (3.3 feet) in carapace length
and 150 kg (330 pounds) in weight. They have a smooth carapace
with four pairs of lateral scutes and a single pair of elongated
prefrontal scales between the eyes. The plastron remains a
yellowish white, but the carapace changes color from solid
black to a variety of shades of grey, green, brown and black
in starburst or irregular patterns. Green turtle
hatchlings are about 50 mm (2.0 inches) long and weight about
25 g (0.88 ounces).
Adult
green turtles are unique among sea turtles
in that they are herbivorous, feeding primarily on seagrasses
and algae. This diet is thought to give them greenish colored
fat, from which they take their name. A green turtle's carapace
(top shell) is smooth and can be shades of black, gray, green,
brown, and yellow. Their plastron (bottom shell) is yellowish
white.
Scientists
estimate green turtles reach sexual maturity
anywhere between 20 and 50 years, at which time females begin
returning to their natal beaches (i.e., the same beaches where
they were born) every 2-4 years to lay eggs.
The
nesting season varies depending on location. In the southeastern
U.S., females generally nest between June and September, while
peak nesting occurs in June and July. During the nesting season,
females nest at approximately two week intervals, laying an
average of five clutches. In Florida, green turtle
nests contain an average of 135 eggs, which will incubate
for approximately 2 months before hatching.
Habitat
Green
turtles
primarily use three types of habitat: oceanic beaches
(for nesting), convergence zones in the open
ocean, and benthic feeding grounds in coastal areas.
Adult females migrate from foraging areas to mainland or island
nesting beaches and may travel hundreds or thousands of kilometers
each way. After emerging from the nest, hatchlings swim to
offshore areas, where they are believed to live for several
years, feeding close to the surface on a variety of pelagic
plants and animals. Once the juveniles reach a certain age/size
range, they leave the pelagic habitat and travel to nearshore
foraging grounds. Once they move to these nearshore benthic
habitats, adult green turtles are almost exclusively herbivores,
feeding on sea grasses and algae.
Green turtles are generally found in fairly
shallow waters (except when migrating) inside reefs, bays,
and inlets. The turtles are attracted to lagoons and shoals
with an abundance of marine grass and algae. Open beaches
with a sloping platform and minimal disturbance are required
for nesting. Green turtles apparently have
a strong nesting site fidelity and often make long distance
migrations between feeding grounds and nesting beaches. Hatchlings
have been observed to seek refuge and food in Sargassum rafts.
Distribution
The
green turtle is globally distributed and
generally found in tropical and subtropical waters along continental
coasts and islands between 30° North and 30° South. Nesting
occurs in over 80 countries throughout the year (though not
throughout the year at each specific location). Green
turtles are thought to inhabit coastal areas of more
than 140 countries.
Threats
The
principal cause of the historical, worldwide decline of the
green turtle is long-term harvest of eggs and adults on nesting
beaches and juveniles and adults on feeding grounds. These
harvests continue in some areas of the world and compromise
efforts to recover this species. Incidental capture in fishing
gear, primarily in gillnets, but also in trawls, traps and
pots, longlines, and dredges is a serious ongoing source of
mortality that also adversely affects the species' recovery.
Green turtles are also threatened, in some
areas of the world, by a disease known as fibropapillomatosis
(FP).
Reproduction
and Development
The
nesting season varies with the locality. In the Southeastern
U.S., it is roughly June through September. Nesting occurs
nocturnally at 2, 3, or 4-year intervals. Only occasionally
do females produce clutches in successive years. A female
may lay as a many as nine clutches within a nesting season
(overall average is about 3.3 nests per season) at about 13-day
intervals. Clutch size varies from 75 to 200 eggs, with an
average clutch size of 136 eggs reported for Florida. Incubation
ranges from about 45 to 75 days, depending on incubation temperatures.
Hatchlings generally emerge at night. Age at sexual maturity
is believed to be 20 to 50 years.
Range and Population Level
The
green turtle has a worldwide distribution in tropical and
subtropical waters. Major green turtle nesting colonies in
the Atlantic occur on Ascension Island, Aves Island, Costa
Rica, and Surinam. Within the U.S., green turtles nest in
small numbers in the U.S. Virgin Islands, Puerto Rico, Georgia,
South Carolina, and North Carolina, and in larger numbers
in Florida. The Florida green turtle nesting aggregation is
recognized as a regionally significant colony. About 200 to
1,100 females are estimated to nest on beaches in the continental
U.S. In the U.S. Pacific, over 90 percent of nesting throughout
the Hawaiian archipelago occurs at the French Frigate Shoals,
where about 200 to 700 females nest each year. Elsewhere in
the U.S. Pacific, nesting takes place at scattered locations
in the Commonwealth of the Northern Marianas, Guam, and American
Samoa. In the western Pacific, the largest green turtle nesting
aggregation in the world occurs on Raine Island, Australia,
where thousands of females nest nightly in an average nesting
season. In the Indian Ocean, major nesting beaches occur in
Oman where 6,000 to 20,000 females are reported to nest annually.
Critical Habitat
50
CFR 226.208 Culebra Island, Puerto Rico - Waters surrounding
the island of Culebra from the mean high water line seaward
to 3 nautical miles (5.6 km). These waters include Culebra's
outlying Keys including Cayo Norte, Cayo Ballena, Cayos Geniquí,
Isla Culebrita, Arrecife Culebrita, Cayo de Luis PeZa, Las
Hermanas, El Mono, Cayo Lobo, Cayo Lobito, Cayo Botijuela,
Alcarraza, Los Gemelos, and Piedra Steven.
Reasons for Current Status
A
major factor contributing to the green turtle's decline worldwide
is commercial harvest for eggs and meat. Fibropapillomatosis,
a disease of sea turtles characterized by the development
of multiple tumors on the skin and internal organs, is also
a mortality factor and has seriously impacted green turtle
populations in Florida, Hawaii, and other parts of the world.
The tumors interfere with swimming, eating, breathing, vision,
and reproduction, and turtles with heavy tumor burdens become
severely debilitated and die. Other threats include loss or
degradation of nesting habitat from coastal development and
beach armoring; disorientation of hatchlings by beachfront
lighting; excessive nest predation by native and non-native
predators; degradation of foraging habitat; marine pollution
and debris; watercraft strikes; and incidental take from channel
dredging and commercial fishing operations.
Management and Protection
In
the Southeast United States, major nest protection efforts
and beach habitat protection are underway for most of the
significant nesting areas, and significant progress has been
made in reducing mortality from commercial fisheries in U.S.
waters with the enforcement of turtle excluder device regulations.
Many coastal counties and communities in Florida have developed
lighting ordinances to reduce hatchling disorientations. Important
U.S. nesting beaches have been and continue to be acquired
for long-term protection. The Fish and Wildlife Service and
National Marine Fisheries Service have been funding research
on the fibropapilloma disease for several years to expand
our knowledge of the disease with the goal of developing an
approach for remedying the problem. Due to the long range
migratory movements of sea turtles between nesting beaches
and foraging areas, long-term international cooperation is
absolutely essential for recovery and stability of nesting
populations.
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