Download Marine Turtles - PROF. ALAN DEIDUN

Marine Turtles – points for article in May issue
Dr. Alan Deidun
Marine turtles are probably one of the most iconic and charismatic components of the
marine environment. Their magnetic appeal may be attributed to the image of haplessness
they convey whilst lumbering on land or due to their resilience and grace when in the
water. Some limelight on aspects of their existence is warranted, especially in view of the
many threats marine turtles constantly face and since they have been around for almost
100 million years, having outlived their dinosaur ‘relatives’.
Seven different species of marine turtles ply the oceans – the loggerhead turtle, the
leatherback turtle, the green turtle, the Kemp’s Ridley turtle, the Hawksbill turtle, the
Olive Ridley turtle and the Flatback turtle. Of these seven species occurring globally, the
first five listed have been recorded at one time or another in the Mediterranean –
however, the undisputed denizen of the Mediterranean is the loggerhead turtle (Caretta
caretta), being the largest hard-shelled extant sea turtle species. They have a heart-shaped
carapace, which is often covered with commensal organisms such as barnacles and algae,
which hitch a hike along with the turtle in its voyage around the world.
Loggerhead turtles reach maturity between 10 and 30 years of age. Courtship and mating
apparently occur most commonly during the migrations to nesting grounds, several weeks
before nesting begins, rather than near the nesting beaches. The male circles the female,
bites her neck and shoulders, and mounts her shell from behind. The pair typically floats
at the surface during copulation. Once the site is chosen, the female first excavates a body
pit using all four limbs and then uses only her rear feet to dig the nest chamber in the
bottom of the pit. After the eggs have been laid, the female covers the nest, first using
only her hind legs and eventually using all four limbs to cover and camouflage the entire
site. Females may lay up to seven clutches per season at intervals of nine to 28 days, most
typically about every two weeks, although four or five clutches per season is more usual.
Most females nest only every two or three years.
The number of eggs laid on a single beach by different turtle species ranges from 25 to
200 and incubation time of eggs is about 2 months. The heat of the sun incubates the
eggs and determines the sex ratio within the population – in fact, if temperatures rise
above 29.9° C the embryos become female, lower temperatures result in male hatchlings.
Eggs hatch usually at night. After emerging from the nest the young turtles must literally
scramble frantically for their lives. Sharks and other large fishes as well as birds pick
them off while they dash to the sea. Although marine turtles breathe air, they can spend
up to 3 hours submerged. Most turtles are mainly carnivores and feed on jellyfish,
tunicates (ascidians, sea squirts), sponges (one of a few animals that eat them), soft
corals, crabs, squids and fishes - in fact, the recent upsurge in jellyfish numbers has been
attributed by some to the decline in turtle numbers, although other factors play a role too.
Some turtles also feed on seagrasses and algae.
Marine turtles are dogged by a major Achilles’ heel – the need to lay their eggs on land
along ever more incipient pockets of undisturbed sandy coastline. Global warming,
through projected rises in sea level, could further erode any remaining beach havens. The
distribution of loggerhead turtles girdles the globe, being found in all tropical and
temperate seas of the world, being rare only in the eastern and central Pacific Ocean.
Marine turtles, including loggerheads, are known for their long, epic migrations,
sometimes equaling 3,000km (the turtles’ migration is tracked through numerous
techniques, with tagging and satellite telemetry being the most commonly-used) – despite
this, genetic studies have stressed the fact that turtles from different nesting areas differ
genetically – this suggest that female turtles return to the same nesting beaches on which
they hatched. Scientists have long racked their brains to decipher which cue/s the female
turtles were using to orientate themselves and locate with great accuracy far-flung islands
and beaches – take Ascension Island, in the Atlantic Ocean, for example – the island is
1,600km distant from the nearest mainland (west coast of Brasil). Despite being such a
backwater, the island witnesses an annual nesting of 6,000-15,000 green turtles, making it
the second largest colony in the world for this turtle species, after Costa Rica. Magnetic
cues – i.e. orientation with respect to the earth’s magnetic field – could be an answer to
the riddle, but no scientific consensus has been reached on the matter so far.
Locally, the last recorded nesting by a turtle on one of our beaches was in 1960 at Golden
Bay (in the Internet Café area), which, at that time, was a far cry from the light-polluted,
cacophonic and congested place it is today. Emblematic of the gulf between yesteryear’s
and today’s conservation ethics, the hapless loggerhead was consumed, along with its
eggs, on that occasion by those observing its ordeal – marine turtle flesh could easily be
purchased on markets for use in soups up to a 10-15 years ago. The closest loggerhead
turtle haunts to our shores are the Spiaggia dei Conigli (‘Rabbit Beach’, in Lampedusa)
and the Tunisian and Libyan shores. The largest populations of loggerhead turtle in the
Mediterranean are, however, encountered in the Levantine Basin (i.e. in the East
Mediterranean), with beaches in Greece (such as Zakynthos Beach), Turkey (such as
Kazanli) and Cyprus (such as Akamas Beach) harbouring the largest numbers of nesting
turtles, although the loggerhead species has even been reported as nesting in the Nile
Delta in Egypt. A number of Marine Protected Areas (MPA’s) have been instituted in
these countries to buttress turtle nesting sites but most of these sites are still competing
with the frenetic upsurge in hotel development. Spiaggia dei Conigli happens to be the
most frequented and popular beach on the island of Lampedusa – despite this, local
tourism authorities have been condescending enough to cordon off part of the beach
during the summer months to bathers, with volunteers paying vigilance round the clock to
any turtle eggs laid in the sand.
In view of their dwindling populations, marine turtles are protected in the Mediterranean
Sea by virtue of numerous agreements, such as the Bern Convention and the RAC/SPA
(Regional Activity Centre for Specially Protected Areas) Protocol, based in Tunis since
1991, and which falls under the auspices of the Barcelona Convention. Of the 6 action
plans devised by the centre to prioritise conservation efforts, one deals with the
conservation of marine turtles and fields a number of important recommendations to
spearhead the conservation of these graceful species. These include the exclusion of
speedboats from areas frequented by turtles, the education in turtle handling techniques
of fishermen and the adoption of Turtle Excluder Devices (TED) along fishing nets and
modified longlines. MEDASSET (The Mediterranean Association to Save the Sea
Turtles) is an international non-governmental organisation (NGO) founded in 1988,
working for the conservation of sea turtles and their habitats throughout the
Mediterranean and which has disseminated numerous toolkits to schools around the Med.
Despite the local dearth in nesting beaches, marine turtles, especially loggerheads, are
quite frequently encountered in our waters, frequently in ignominious ways (i.e. either by
fishermen when they inadvertently swallow fishing hooks with bait or plastic material
(mistaking it for jellyfish) and through horrendous collisions with pleasure seacraft.
Injured and maimed turtles are ferried to the Malta Centre for Fisheries Sciences (MCFS)
at San Lucjan Tower in Marsaxlokk, which has the necessary expertise and facilities to
fully rehabilitate the turtles (which may include carrying out surgery on the turtles) to
release them back into the wild at a later date. The Marine Rescue Team of Nature Trust
is a team of dedicated volunteers whose main objectives are to rescue and rehabilitate
dolphins, whales and turtles found in the Maltese waters, to collect and compile data to
identify causes of injury and or deaths so as to contribute to scientific knowledge through
monitoring and to raise funds to buy much needed equipment such as stretchers, dinghies,
etc. The volunteers receive regular training from experts in the field. The NGO is also
aiming to open a wildlife rehabilitation clinic, costing in the region of Eur 200,000, by
the year 2010, of whose services even injured marine turtles will hopefully benefit.
BICREF is another NGO which is conducting useful work too in such a field.
Next time round, Dr. Alan Deidun will turn the spotlight on bluefin tuna