Ingvild Maehle (veterinary student, 1st year)
13.04.2004
Kingdom: Animalia
Phylum: Chordata
INTRODUCTION
The Caretta caretta has a large head
caused by the space needed for muscles closing the jaw. The shell is
patterned with many octogons, with the characteristic line of five octogons
going from the head to the tail-end of the shell. The hatchlings are
of a very dark brownish-black colour, while the adult turtles are reddish-brown.
The limbs are dorsoventrally flattened flippers used for swimming and
creating nests. Because of their heavy weight, the loggerhead turtle
moves slowly when on land. They are hardly ever out of the water, except
for when laying eggs on beaches. There are two subspecies to the Mediterranean
Caretta caretta. The one found in the Indian and Pacific oceans is the
C.caretta gigas, and the one in the Atlantic region is the C. caretta
caretta. The differences are not many, apart from the Atlantic species
bearing two claws on their front flippers.
The Caretta caretta is so-called
ectothermic, meaning they use heat from the environment and physical
activity to regulate their body-temperature.
The Caretta caretta has its habitat
in open sea, but comes near the shore in bays or sounds in the nesting
season. They can however travel many hundred miles from shore to get
to warmer climate depending on the season. The loggerhead turtle is
concidered herbivore, invertivore and piscivore, meaning it will eat
sea-plants, marine invertebrates (crustaceans, molluscs etc.) and fish.
They usually feed at the bottom of the sea, but might feed on jellyfish
at the surface. The hatchlings eat small pieces of crustaceans at the
surface.
Nesting season for the Caretta caretta
is usually from May to August, and hatching of the eggs is between July
and October. The incubation period is around two months.
In
the Mediterranean, a sea-turtle conservation project has been running
for many years, by the Greek organization Archelon. They work to protect
and monitor the Loggerhead’s main nesting areas on the Greek islands
of Crete, Zakynthos, Kephalonia and Pelopponesus. In Athens, a Sea turtle
rescue and rehabilitation-centre has been established, where veterinarians
treat injured sea turtles from all over Greece.
MAJOR THREATS TO THE LOGGERHEAD POPULATION
IN THE MEDITERRANEAN
The biggest problem to establishing
a constantly increasing sea-turtle population in the Mediterranean is
the very high mortality-rate of newly hatched turtles. In a single turtle-nest,
there can be over a hundred eggs, and there can be over a hundred nests
on the same beach. This would make a total of many thousand new hatchlings.
Unfortunately only a few out of a thousand hatchlings are believed to
reach adult age. This is not a case for only populations on the verge
of exctinction, but also for stable populations.
There are many different threats
to the turtle populations. We can in general distinguish between natural
threats caused by abiotic and biotic factors, and threats caused by
humans.
Natural Threats:
-
Biotic
-
disease
-
predation at sea
-
predation at nesting sites
Abiotic (non-living)
-
flooding/storms
-
driftwood, seaweed etc
-
Threats caused by humans
-
At Sea
-
fishing
-
pollution
-
boat collisions
-
Nesting beaches
-
sea defences
-
quarrying/mining
-
pollution
-
noise - general beach
-
light
-
roads and illegal buildings
-
beach obstacles
-
food e.g. eggs for eating by man
-
sand compaction
-
drainage
The hatching of turtles is a complicated
process. A turtle is usually reproductive for about 30 years, if they
survive childhood. As an adult turtle, there are many threats. Turtles
are often caught in fishermens’ nets which means they can’t get to the
surface to breathe and will eventually die, they can get hit by boats,
get attacked by shark e.g.
If a turtle grows to reach reproductive
age, they will return to the beach on which they were hatched. Sometimes their beach has been completely taken
over by tourism, or rise of sea-level has flooded the beach. This means
that the turtles won’t be able to lay their eggs. To lay its eggs, the
adult turtle crawls up on the beach to dig a nest (ca. 40 cm deep),
and usually lays around 100 eggs. However, because of humans, the sand
often gets very compact and hard (people running and playing, sun-beds,
umbrellas etc.). This makes it impossible for the turtles to dig a nest,
and will eventually return to the sea an abort its eggs.
After about two months of incubation,
the hatclings crack open the egg-shell and crawl to the surface of the
sand. It is also important at this stage that the sand isn’t compact
since the hatchlings aren’t very strong and won’t be able to crawl through
the sand to the surface.
When they reach the surface, the
hatchlings automatically go to the brightest light. This is beacause
originally the sea was the brightest light, and the hatchlings have
to go straight to the sea. These days, the brightest light might be
the light from bars, restaurants, shops and cars. There have been many
incidents where hatchlings have approached bars thinking it is the sea,
and eventually “drowned” because of the lack of water. On the Greek
island of Zakynthos, one can notice extreme differences in number of
successful hatching in different areas. A secluded area has been devoted
to turtles as a National Marine Park. Only Marine Park guards are allowed
in here, and there are no lights. The number of nests and turtles in
this are is many times higher than in the populated lit-up tourist-areas
close by. Many places, there has been positive reports to building of
sand dunes or planting shrubs as a light barrier.
On the way from the nest to the sea,
many hatchlings are taken by birds or small animals. The ones that eventually
make it to the sea will because of their size face many threats, for
example being eaten by bigger fish.
The gender of the hatchlings is determined
by the surrounding temperature while they are in incubation. A warm
temperature will give females, a colder temperature results in males.
Some researchers believe that global warming will eventually cause only
hatching of female turtles. This will again result in an end to the
reproduction and eventually extinction of the Caretta caretta. The shade
from beach-towels, sun-beds and umbrellas is also a major source of
cooling down the sand, and thereby also cooling down the eggs and influencing
the gender.
Many boats in popular tourist-areas
offer so-called “turtle safaris” where tourists are promised to see
turtles. Most people think this is a fantastic chance for them to see
the animal in its own environment, without causing any damage. The boat
localizes a turtle, and as it drives up to it, the turtle usually dives
down into the water. After a while, the turtle usually comes back up
to the surface. The tourists see the turtle as being friendly and interested
in the boat, and believe that is the reason for the turtle coming back
up again. What they tourists don’t
know, and what the “turtle-guides” take advantage of is that a turtle
can’t stay under water for an unlimited time, but has to ascend to the
surface to breathe. They can usually hold their breath for a long time,
but when stressed they start hyperventilating. This means they have
to breathe more often, and therefore have to go to the surface, where
they get even more stressed by all the tourists with their cameras and
excited laugh. There have been reports on turtles forcing themselves
to stay underwater, and thereby drowning themselves.
Possible conservation efforts and
improvements
As stated earlier, there are many
threats that are lethal to the turtles, but many can easily be changed,
or at least reduced. The Archelon organization is working hard to raise
public awareness on the vulnerable nests and animals, as well as working
to protect the beaches. There are still many things that require bigger
resources and finances. If a national plan for sea-turtle conservation
would be made, it would be easier for the organization to get approval
among the natives on the islands. Many of the islands have areas owned
by foreign investors whose only concern is building hotels, not caring
if it is in a turtle-nesting area or not. Raising awareness with the
fishermen, finding a solution to the problem of turtles getting trapped
in nets, having restricted areas where speed boats and jet-skis aren’t
allowed will prevent injuries caused by collisions. There should be
secluded areas with undeveloped beaches, unused by humans. Different
lights may be used in bars, some lights seem to attract turtles less,
and therefore will not disorientate them away from the sea. Predator
control might be effective in areas heavily affected by attack of hatchlings
by e.g. racoons or foxes, maybe by cages protecting the nests?
There have been successful incubation
of eggs in man-made polystyrene incubators, these might be a solution
for nests that need relocation e.g. because of erosion or nests in areas
exposed to humans.
Many things could be changed for the benefit of the Caretta caretta,
both with and without economical contributions. A general public awareness
would improve the local conditions, a national awareness would make
a noticeable difference in a much larger scale. Maybe it is too much
to hope for a helping hand in conservation of an incredible species.
It is hard finding a solution to this problem, maybe we have to accept
the fact that we’re adding another animal to the list of animals we
have driven to exctinction.
 |
 |
 |
Information station |
Morning survey |
Turtle tracks |
 |
 |
 |
Excavation |
Hatchling |
Turtle swimming to shore |
Literature and scientific articles
I have used for the essay:
Bjorndal, K. A. Biology
and conservation of sea turtles.
