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Deepseawaters
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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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