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Marine
turtles have lived in the oceans for over 100 million years.
Evolving in the Triassic period, outliving the dinosaurs, turtles
remain an integral part of the traditional culture of many coastal
peoples throughout the world. Once there were 200 species of turtles
on earth. Of the seven surviving species of marine turtles in
the world, six occur in Australian waters. Increasing threats
to marine turtles has resulted in five of the six species that
occur in Australian waters being listed on the Commonwealth’s
Endangered Species Protection Act, 1992. Loss of habitat, the
over harvesting of turtles and eggs, commercial fishing practices
and pollution place all turtles under threat. Whilst all turtles
are at risk, the Green turtles are hunted more regularly than
other species. Indigenous communities prefer to eat the Green
turtle as it lives as an adult on a diet of seagrass and seaweed
unlike other species of turtles.
There are four major nesting areas distributed across
the top of Australia. From these sites Green turtles
migrate between Australia and Indonesia, spending long periods
at sea travelling an extraordinary 3000 kilometre journey from
birth to adulthood. Valuable tagging programs now trace the movement
of individual turtles as little is known of the journeys made
over a thirty to fifty-year period. Through genetic sampling,
scientists are able to identify breeding groups and origins. The
ability to return to the same beach is linked to the bearings
imprinted on the internal compass of the hatchlings as they turn
clockwise before entering the water. Tragically many females return
to their place of birth to encounter concrete paths, cities, dirty
ports and hotels. Females breed for several decades and often
mate with more than one male.
Although the female carries hundreds of eggs at a time
and may return several times to lay her eggs, the survival rate
of hatchlings is quoted at 1%, as baby turtles are vulnerable
to a wide range of predators from the time of birth.
The incubation time and sex of hatchlings is dependent on the
temperature of the sand. The warmth of the dark volcanic sands
around Indonesia produce females and the cool white sands of Australia
result in mostly males. The eggs are round, white and resemble
a ping pong ball. The hatchlings take several days to dig their
way to the surface and then begin the difficult journey to the
sea. Whilst birds, crabs, fish, monitor lizards, Komodo dragons,
foxes and wild pigs devour many of the newly hatched it is humanity
that has proven the greatest threat to the species. The sale of
turtle sate on the streets of Bali and the belief in turtle eggs
as a tonic for male virility have decimated the number of turtles
in our waters. Ten years ago in Indonesia 70,000 eggs were harvested
and sold by one community in a two-week period.
Green turtles are easily identified by their high domed
carapace and the four large costal scales on either side of the
shell. The adult carapace is about one metre long and
the colour of the shell is light to dark green with mottling.
They can be easily distinguished from the Hawksbill turtle that
has thick overlapping carapace scales and grows to only 0.8 metres
in length and the large leatherbacks that have no scales, just
five long ridges along the carapace.
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Research Activities
Secondary Students
Make a turtle identification kit. Research the different
species in Indo/Pacific region and to look carefully at
their exterior shells (carapace). Observe the pattern, structure
of the different species.
Map the worlds turtle populations and identify the oceans
that are home to the Green Turtle. Record the ocean currents
and winds travelled by the turtles between Australia and
Indonesia.
Primary Students
Draw the life cycle of a turtle. Illustrate the many stages
of development of the turtle beginning with the egg hatching,
the orientation process, entering the sea, the journey,
the encounters, the meeting with the male and the return
to lay eggs.
Create a time scale celebrating the antiquity of sea turtles
— the world’s oldest reptiles, around since
the age of dinosaurs and in serious danger of becoming extinct.
Go to www.euroturtle.org
and explore the structure of a turtle.
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