Sea turtles are an important part of cultural history for
people all over the world. Ancient myths and legends present the
turtle as a symbol of strength, stability and wisdom. A Chinese
myth tells the story of the creation of the earth occurring on the
shell of an immense turtle. Many other cultures, such as the Greeks
and Egyptians, considered the turtle to be sacred. In Bangkok, Thailand,
for example, turtles are a sign of immortality. Even today, people
give special significance to turtles. They are beautiful, graceful
animals, very important to both the environment and to societies
both as food and for trade.
There are eight different species of sea turtles alive today:
The Green Turtle (Chelonia
mydas) is a circumglobal species and is the most common of the
eight sea turtles. The green turtle can be recognized by a single
pair of scales in front of the eyes rather than 2 pairs of scales,
which most sea turtles have. They are one of the largest species
of sea turtles: their shells can be up to 3 ft long, and they can
weigh up to 300 lbs. They are called green sea turtles for the color
of the fat under their shell, not for the actual color of the shell,
which can range from a greenish shade, to brown, black, or even
gray. The green turtle feeds on seagrasses
and seaweed. Its important nesting and feeding grounds are in the
tropics. It has long been harvested for meat and eggs in Costa Rica,
Caribbean, Indonesia, and Panama. Its cartilage is used in Asian
countries for turtle soup.
The Black Turtle (Chelonia
agassazii), which is named for the black or gray color of its
shell, is confined to the Eastern Pacific Ocean. It is protected
in the Galapagos and nominally in Mexico. They are still subject
to illegal harvest, and are on a decline.
The Flatback Turtle (Natator
depressus) live only in the waters of Australia where it is
protected by law, with the exception of aboriginal harvest. It is
named for its flat shell, and can grow up to 39 inches long and
198 lbs.
The Loggerhead (Caretta
caretta) has an anti-tropical distribution. It is found in Northern
and Southern Indian Ocean, Australia, Japan and the Southeastern
US. The loggerhead can be identified by its large head as well as
by a reddish brown carapace (upper shell) and dull brown or yellow
plastron (lower shell). The loggerhead can grow between 32-41 inches
and can weigh up to350 lbs. This turtle doesnt suffer from
poaching or capture for meat, but rather from accidental capture.
It has powerful jaws for eating shellfish living on the bottom of
the ocean.
The Hawksbill (Eretmochelys
imbricata) is subject to intense intentional trade. Its beautifully
patterned shell is a source of tortoiseshell used to make jewelry
and combs. Its narrow head and beak make it look like a hawk, owing
to its name. This is one of the smaller sea turtle species. It only
grows 30-36 inches and weighs100-150 lbs. It is common on tropical
reefs in the Caribbean islands and Australia. It is smaller than
the green sea turtle and its shell is reddish brown with yellow
streaks. It feeds on encrusting animals such as sponges, sea squirts
barnacles, and seaweed.
The Olive Ridley (Lepidochelys
olivacea) nests mainly in the Pacific Ocean, around Costa Rica,
Mexico and Nicaragua, as well as the Northern India Ocean. It is
the most abundant species of sea turtle, as well as one of the smallest,
weighing less than 100 lbs. It is olive
green in color, giving it its name.
The Kemps Ridley (Lepidochelys
kempi) is the rarest species of sea turtle as well as most endangered.
Kemps Ridley is the smallest sea turtle, only growing to be
24-28 inches and weighing 77-100 lbs. Its carapace is olive green,
and its plastron is yellowish. This turtle only nests on one beach
in the world, in Rancho Nuevo, Mexico. In 1942, in only one day,
42,000 Kemps Ridleys could be seen nesting on this beach.
In 1995, there were only a total of 1,429 nests.
The Leatherback
(Dermochelys coriacea) is exploited for eggs. Its Atlantic
colonies seem to be secure from disruption, but other sites have
declined. It is the largest sea turtle- growing up to 7ft long and
weighing at least 1,200 lbs. Instead of a hard shell, it has thin,
tough, rubbery skin. Five distinct ridges are formed by small bones
buried in their skin. Its carapace is black with white spots while
the plastron is whitish to black. This turtle lives in the open
ocean, it can dive the deepest and travel the furthest of any other
sea turtle. Its body shape is very streamline; it has powerful front
flippers to aid in strong swimming. It is rarely seen except on
nesting beaches. Jellyfish are the main component of their diet.
Reproduction in sea turtles:
Mating: During the mating season, all species of marine
turtles migrate from feeding areas to mating areas. After mating,
the males then return to foraging areas while the females proceed
to nesting beaches. Some turtles migrate more than 2600 km, but
most travel less than 1000 km. Female turtles do not usually reproduce
every year, except for Kemps Ridley. Males may breed every
year. Mating can occur anywhere in the water but usually occurs
at the surface. Mating is not gentle. The male bites the females
flippers and neck. Her shell gets clawed from the males large
claws on the hind and front flippers that hold him in place. The
male may also get attacked from other males during this process.
Males will bite other males tails and flippers. Turtles can
stay together while mating for about 10 hours.
Nesting: Most females lay several clutches of eggs, which
reduces the likelihood of all eggs being lost. This can be done
at 2-week intervals. When nesting, turtles generally escape the
heat by creating their nests at night, except for the L. kempi
and N. depressus. Eggs hatch after 6 to 13 weeks of incubation
depending on the temperature. They generally hatch in the early
evening. They can tell whether it is evening or daytime based on
the temperature of the sand. They dig toward cooler sand; if they
start digging and the sand gets progressively warmer they wait until
the sand cools. If they hatched during the day they would have to
face excessive heat and predation.
Navigation: After hatching, sea turtles primarily
use vision to find the sea, orienting themselves toward the brightest
light, presumably the moon. They move away from elevated silhouettes,
such as sand dunes and vegetation. Turtles also rely on wave cues
to swim offshore, moving toward approaching waves. They sense the
wave motion under water by monitoring the sequence of accelerations
they experience in the water column. Loggerhead and leatherback
hatchlings use internal magnetic compass orientation. Turtles emerge
from their nests without an established directional preference.
They acquire a directional inclination while crawling on the beach
toward a light source. This sets their magnetic compass. They do
not have a polarity-based system but an inclination system, which
means they follow the intensity of the earths magnetic field
and not the poles.
Conservation: Sea turtles worldwide are being protected
under the endangered species list and by federal agencies. Efforts
are being made to develop local help and to educate locals on the
importance of these marine reptiles, not only for the future generations,
but also for the health of the environment. Unfortunately, sea turtles
are still being killed in drift nets, disoriented by street lights,
taken as eggs for alcoholic beverages, and are killed as adults
for souvenirs, food and shell products. Worldwide, help is needed
from both young and old to save these remarkable ancient, endangered
animals. Currently, there are several different attempts being made
to help protect these species and increase their populations. Shrimp
trawling is a large problem for sea turtles, many get caught in
the nets and drown. TEDs (Turtle Exclusion Devises) have been
developed to reduce sea turtles getting caught in these nets. TEDs
are trap doors in the nets that allow the sea turtles, but not the
shrimp to escape. Shrimp farms are also being started. Instead of
harvesting the shrimp, which can cause the accidental capture of
the turtles as well as other marine animals, shrimp are being raised
in farms. Turtle hatcheries have also helped reduce the decline
of sea turtles by removing the eggs from nests where they may be
eaten by predators or removed by poachers. The eggs are taken to
the hatchery where they are incubated and later released.
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