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Sea Turtle Facts
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Factsheets
Flatback
Green Sea Turtle
Hawksbill Kemps
Ridley
Leatherback
Logggerhead
CHARACTERISTICS
Adult males and females are equal
size. The leather back sea turtle is the largest sea turtle reaching about 105cm in
length and about 101kg in weight.
They may be olive-green, yellow, greenish-brown, or black in color.
The sea turtle is known for its large shell. It cannot retract it head and limbs
under its shell as land turtles can. The large, bony shell provides protection from
predation and abrasion. The shell is covered with a layer of horny plates called
scutes.
Sea turtles do not have large upper eyelids that provide protection for their eyes. They
do not have external ear openings. They do not have teeth.
HABITATS
Sea turtles are found in warm seas throughout the world.
Adults are found in shallow coastal waters, bays and lagoons. Some sea turtles migrate from feeding grounds to nesting grounds, others nest and feed in the same general area.
Diet varies with species. Sea turtles may be carnivorous (meat eating), herbivorous (plant eating), or omnivorous (eating both meat and plants). The jaw structure of many species indicates their diet.
For example:
1. Green and black sea turtles have jaws that are adapted for a vegetarian diet of sea grasses.
2. Loggerheads' and Ridleys' jaws are adapted for crushing and grinding. Their diet consists primarily of crab, mollusks, shrimps, jellyfish and vegetation.
Some types of sea turtles change their eating habits as they age. For example, green sea turtles are mainly carnivorous from hatchling until juvenile size; they then shift to a herbivorous diet.
REPRODUCTION
Like other turtles, sea turtles lay eggs. They
must come ashore to do so. For most types of turtles the females usually nest during the
warmest months of the year. The exception is the leatherback turtle, which nests in fall
and winter. Most females return to the same nesting beach each year. Recent
studies suggest that some females of some species will visit more than one nesting beach
in a season.
Females usually come ashore at night, alone, most often during high tide. A female turtle
crawls above the high tide line and using her front flippers, digs out a "body
pit." Then using her hind flippers, she digs an egg cavity. The depth of the
cavity is determined by the length of the stretched hind flipper.
Depending on the species, the female deposits 50 - 200 eggs into the egg cavity. The eggs
are soft-shelled and are papery to leathery in texture. They do not break when
they fall into the egg cavity. The eggs are surrounded by a thick, clear mucus.
The female covers the nest with sand using her hind flippers. Burying her eggs serves three purposes;
1. protects the eggs from predators
2. helps keep the soft eggs from drying out
3. helps the eggs to maintain proper temperature
Experts can identify the species of turtle
by the type of mound left by the nesting female and by her flipper tracks in the sand.
Females may spend two or more hours out of the water during the entire nesting process.
Females usually lay between one and nine clutches (groups) of eggs per season.
It is possible that through the storage of sperm from one or several males in the oviducts
of the females, all clutches of the current nesting season may be fertilized without
repeated matings.
Females may nest every two to three years. Sea turtles hatch throughout the year but
mostly in summer.
Incubation time varies with species, clutch size, and temperature and humidity in the
nest. The incubation time for most species is 45 to 70 days. Research indicates that
the sex of an embryo is determined sometime after fertilization, as the embryo develops,
and may be temperature dependent. Lower nest temperatures produce more males; higher
temperatures produce more females.
HATCHLINGS
Hatchlings use a caruncle (temporary egg tooth) to help break open the shell. After hatching, the young turtles may take three to seven days to dig their way to the surface. Hatchlings usually wait until night to emerge from the nest. Emerging at night reduces exposure to daytime predators. They leave the nest and head to the water in groups. Studies have shown that some nests will produce hatchlings on more than one night.
There are several theories as to how
htachlings find the sea. Hatchlings may discriminate light intensities and head for
the greater light intensity of the open horizon. During the crawl to the sea, the
hatchling may set an internal magnetic compass, which it uses for navigation away from the
beach.
When a hatchling reaches the surf, it dives into a wave and rides the undertow out to
sea. A "swim frenzy" of continuous swimming takes place for about 24 to 48
hours after the hatchling enters the water. This frantic activity gets the young turtle
into deeper water, where it is less vulnerable to predators. There have been reports
of swimming hatchlings diving straight down when birds and even airplanes appear overhead.
This diving behavior may be a behavioral adaptation for avoiding predation by birds.
During the first year, many
species of sea turtles are rarely seen. This first year is known as the "lost
year." Researchers generally agree that most hatchlings spend their first few
years living an oceanic existence before appearing in coastal areas. Although the
migratory patterns of the young turtles during the first year has long been a puzzle, most
researchers believe that they ride prevailing surface currents, situating themselves in
floating seaweed where they are camouflaged and where they can find food.
Research suggests that flatback hatchlings do not go through an oceanic phase. Evidence shows that they young turtles remain inshore following the initial swim frenzy. Most remain within 15 km (9.3 miles) of land.