Of Leatherbacks and Loggerheads

Conservation efforts here have seen the population of leatherbacks on South African shores increase nearly five-fold in 33 years - a commendable achievement in light of the fact that nesting populations elsewhere in the world have shown steady declines. .

Vacationtechnician personalized luxury adventure travel transports you to the most exquisite wilderness and chill out retreats on Earth. Conserving rare biodiversity through low volume tourism; our aim is your indulgence -at no one's expense. Plan now to be assured a rejuvenating escape at a restful pace -to an unspoilt gem in the purest sense.

Stuck at 1200 metres! This is the maximum depth the apparatus can register and it looks as though it has imploded. Could this creature possibly have dived more than a kilometre under the sea - an air-breathing leatherback sea turtle? As more nesting females come ashore to lay and are logged in one after another, each confirms this truly remarkable feat. Depth-recording devices attached to their backs, some also broken, others still functioning, show quite clearly that the leatherback, the largest and most powerful sea turtle alive today, is capable of diving even deeper than the known records of sperm whales.

Even if it weren't such an accomplished diver, the leatherback turtle Dermochelys coriacea would be an extraordinary animal. It grows to three metres in length with a flipper span in excess of two metres, and has been known to reach a weight of more than 900 kilograms. It is likely that the very largest individuals recorded could exceed a tonne.

And this marine reptile has power to match. The late Archie Carr, one of the most remarkable and influential sea turtle biologists, enjoyed recounting the tale of some fishermen in the United States who had captured a leatherback and brought it back to harbour. The turtle had displayed little interest in proceedings until, despite being apparently securely corralled in a stout wooden enclosure on the quayside, it suddenly decided to go back to the water. It smashed and bit its way through stout planking and poles, destroyed two wooden rowing boats, plunged into the harbour and swam leisurely out to sea, leaving behind a stunned and gawking audience.

Leatherbacks have that effect on people - not only because they are huge, powerful creatures, but because they are also beautifully formed - streamlined, with seven longitudinal ridges on the carapace and soft, smooth skin. The upper surface of the turtle is almost black, but covered to a greater or lesser degree with blue rosettes similar in size and shape to those of a leopard. Every turtle has a red blaze on the top of the head, thought to be caused by the stretching of the skin as the animal grows.

It is hard to reconcile that these huge marine reptiles start their lives as 50-millimetre-long hatchlings, when they emerge from deep nests on the beaches of Maputaland some 60 days after the billiard-ball sized eggs (over 100 of them in each clutch) are laid in a painstakingly dug hole in the sand. The hatchlings that struggle to the surface are covered with thousands of small scales which may endure for a year or so, but thereafter the scales are stretched flat as the animal grows to its full mass - possibly 2 000 times its original weight.

Few hatchlings do survive to old age or even nesting maturity, however, because the sea is a hostile environment. To ensure that some do live to perpetuate the species, leatherbacks, in common with all sea turtles, put as many hatchlings as possible into the sea each summer. This serves to swamp predators, ensuring that at least one, if not two hatchlings out of every thousand reach adulthood to repeat the process. The Maputaland leatherbacks lay up to seven clutches each season and, although the occasional female re-nests in consecutive seasons, most repeat-nesters return at irregular intervals of two to five years, to lay another 600-700 eggs. One female has visited the Maputaland shores seven times over 18 years and is confidently expected to return for many more seasons to come.

Leatherbacks nest widely on tropical beaches around the world, reaching staggering numbers - thousands a night at some sites. This doesn't happen in Maputaland, however, where 30 years ago the leatherback nesting population was nearing extinction from the taking of eggs rather than the killing of adult females. Conservation efforts here have seen the population of leatherbacks on South African shores increase nearly five-fold in 33 years - a commendable achievement in light of the fact that nesting populations elsewhere in the world have shown steady declines. Sadly, fears of extinction within the next decade now face some of the most famous rookeries, such as the Trengannu beaches of Malaysia.

When not nesting, leatherbacks travel the world pursuing their almost sole source of nutrition - jellyfish. They graze through fields of the invertebrates near the surface in the temperate oceans, dive to more than a kilometre in the tropics where deep down swim thousands of fluorescent jellyfish, and have even been seen happily pursuing their prey amid the icebergs of Labrador. There is, in fact, virtually no major or minor ocean current that does not carry leatherbacks.

Because of their wide distribution, leatherbacks have long interacted with man - undoubtedly their size contributed to the store of tales of sea monsters in ancient times. Even in modern times a surfacing leatherback, carried into Scottish waters by the Gulf Stream, frightened a local angler in his small boat and gave rise to the legend of the 'Soay Beast' - so named after the island off which the sighting took place.

The leatherback is no monster, but an elegant product of evolution, the sea turtle most perfectly adapted to its oceanic existence and worthy of South Africa's conservation efforts. Every summer for tens of thousands of years, leatherbacks have converged on the south-east African coastline and females, even today, nest on beaches from Storms River mouth (but rarely) up into Mozambique, well north of Maputo. In current times, however, the major nesting area lies in the St Lucia and Maputaland marine reserves - a combined protected area including 170 kilometres of beaches, the largest marine park in Africa.

Indeed, the park owes its existence to the nesting presence of the leatherbacks and the more numerous but much smaller loggerhead turtle, for they were the two species that triggered conservation efforts along this stretch of coastline 33 years ago. Ironically, however, when the first conservation steps were taken, the Natal Parks Board staff thought neither of loggerheads nor leatherbacks as they were convinced that it was the green turtle that was coming ashore to nest. The discovery of nesting leatherback turtles thrilled South Africans as few other non-mammal species ever has - and the magic has not dimmed.

Neither is the magic any less with the loggerhead turtle Caretta caretta, even though this less prepossessing reptile lacks the obvious power and grace of its celebrated relative. Neither large nor small, the loggerhead averages about a metre in overall length, is a dull brick red in colour, is not particularly fast and has an extremely large head, somewhat out of proportion to its body, from which it derives both its common name and its slow and unimaginative image. The ugly duckling of the sea turtle family? Maybe ... but such cavalier dismissal would be far from deserving. On the contrary, the loggerhead merits enormous respect as an enduring creature that has colonized the oceans of the world over tens of millions of years.

Loggerheads are admirable, long-distance navigators, faithful to the nesting grounds on which they were born, and so powerfully loyal to their feeding grounds that, on completing a nesting season, they will swim more than 80 kilometres a day for months to get back home. The record one-way swim for a loggerhead known to nest on the Maputaland coast is 3 300 kilometres - to Burgabo Island in southern Somalia!

The fact that any loggerhead can survive to the age where he or she can reproduce and establish a territorial feeding ground is in itself no mean achievement. The path to reproductive success is more dangerous than can be imagined, starting the moment a female lays her clutch of 120 eggs, perhaps the last of the four or five clutches laid during an average season.

Buried 60-70 centimetres deep in the sand of the Maputaland beaches, loggerhead eggs have nearly two months to incubate, warmed only by the ambient temperature and the warmth generated by the incubation of the eggs themselves. At threat from natural disasters such as destructive spring tides or too-extended south-easterly winds which can sweep away all the covering sand and expose the eggs to the sun, there are also natural predators such as the monitor lizard and side-striped jackal, apparently quite capable of scenting the eggs after all traces of the surface nesting disturbance have been smoothed away by the winds.

If laid too close to beach vegetation, roots can grow through the clutch and bind the eggs and emerging hatchlings in a fine mesh from which few can escape. An additional and almost certainly fatal threat is an invasion by red ants - the Dorylids - whose careful removal of egg contents is accompanied by the infilling of eggs with sand so that the entire clutch appears normal apart from the tiny holes through which thousands of ants have terminated another link in the chain of turtle generations.

For all the losses (some 20 per cent of all clutches), thousands of hatchlings will eventually slash their way through the now-brittle soft eggshell using the egg-tooth at the end of the bill and will collectively struggle upwards from their birthplace.

From this point on, any weakness manifested by a hatchling will mean its certain elimination by the obstacles that lie ahead. If a hatchling hatches late and not synchronously with its siblings, it will be buried by the sand brought down by the siblings' departure. A weak flipper or a failure of the urge to climb leads to a similar fate. The faulty genes don't make it to the surface.

Driven now by an urgency dictated by ghost crabs, loggerhead hatchlings orient using light and slope in a direct scrabble for the sea. No time is wasted as they run the gauntlet of ghost crabs, which on average catch and devour four out of every hundred hatchlings. Every second's delay caused by deep vehicle tracks in soft sand or a physical shortcoming in the hatchling itself, greatly increases the chance of dying. So hatchlings move with absolute commitment until they are smashed back by an incoming wave - the first experience of their future home and destiny.

Recent research by Kenneth Lohmann and his colleagues has shown clearly that selection has again equipped the hatchlings for survival. They orient out to sea by swimming directly into incoming waves striking them at exactly ninety degrees. They maintain this heading, even when underwater, until they are beyond that part of the shore which can influence wave direction - they then appear to change to a geomagnetic compass heading and hold that course until striking the Agulhas Current after a few days of non-stop swimming.

Nature has equipped the young turtles with sufficient food reserves in the form of yolk to maintain this swimming frenzy for up to five days, after which time they must start feeding themselves. In the waters off the northern KwaZulu-Natal coast, such reserves are sufficient to see thousands of hatchlings well within the influence of the warm, food-rich Agulhas Current which bears them away on a voyage lasting a decade or more.

Unable to swim free of the mighty current, the hatchlings are swept down the east and south coasts of South Africa. But here and there the Agulhas throws out massive gyres of warm water into the south Indian Ocean, each one bearing any number of turtle hatchlings. The gyres spin away to merge with the gently revolving ocean which will eventually, five to ten years later, bring the surviving hatchlings back as sub-adults to Madagascar and the south-east coast of Africa.

No one has followed this massive movement in detail but it is clear that turtles spend virtually their entire lives on the surface, feeding on bluebottles, storm snails, pteropods and, in short, anything edible. Or even inedible: many sample hatchlings have been found with tiny tarballs and plastic beads in their stomachs.

As they grow, loggerheads rapidly develop sharp spines at the projecting end of each carapace scale and this is their sole protection against being eaten until they have grown beyond the mouth-size of their predators. Few will survive the journey, and even fewer will eventually make it as nesters.

The gauntlet of predation from the kingfish, tuna, cuttlefish and octopuses that scythe through their flotillas is but one the tiny turtles must run, for they must also avoid the massive strandings and death from being caught by cold, upwelling waters close inshore along the Cape coast. Chilled and immobilized, many are blown on to the beaches where gulls and the sun soon kill them. Even so, some survive and are swept around Cape Infanta in patches of Agulhas water which, in late autumn, move into the Atlantic Ocean.

Although now completely off course for an eventual return to the beaches of their origin, these living samples of Maputaland turtle genes may still make a contribution to the survival of the species elsewhere. Some certainly have, as the mitochondrial DNA fingerprints of South Africa's loggerheads overlap significantly with those of loggerhead populations in the Mediterranean thousands of kilometres to the north, and it is highly likely that the loggerheads that colonize West Africa, the Cape Verde Islands, the Mediterranean and eventually the east coast of North America, derived from strays floating away from Maputaland's beaches.

For the sub-adults that do spill out into the southern Indian Ocean to make the circuitous trip back to the waters of Madagascar and eastern Africa, their odyssey is far from over. The final growth to maturity of the returning loggerheads - 15-30 years in all - is also characterized by a nomadic lifestyle, but now the wandering is more deliberate. Coastal survival incurs greater energy demands than floating at the whims of currents. For instance, young loggerheads must dive to greater and greater depths to find food such as mussels, bivalves, gastropods, crayfish and urchins. Soon the goose barnacles, passengers that attach themselves to growing carapaces during the turtles' life adrift, have gone, only to be replaced with acorn barnacles capable of withstanding the pressures experienced at depths of 100 metres or more. These barnacles will stay for life.

The next challenge facing the sub-adult is to find a territory. This is not easy and, while diving for food, encounters with experienced and determined adult loggerheads are likely to precipitate a hasty retreat from the resident's territory. And so the adolescent will move on, and on, perhaps covering thousands of kilometres over several years before finding a vacant site where there is sufficient space and food to allow growth to maturity. As the years pass, and gathering strength and confidence, the now-territorial turtle will in turn drive off any of the youngsters wishing to share its exclusive feeding domain.

The biological clock continues to tick, however, and after an almost risk-free existence for a variable number of years, an instinctive urge to procreate prompts further journeys. So powerful is this instinct that in August, September and October, hundreds of loggerheads will leave the sanctuary and comfort of their feeding territories and make their lonely and dangerous voyages towards what is to them a totally unknown destination. Many undoubtedly die on the trip to Maputaland or back - virtually all recoveries of tagged females are taken in these migratory movements - but most will make it. Lying offshore of a beach of which they have no conscious memory, they will encounter other loggerheads and the cycle of reproduction begins again. Males court and mount females, fertilizing thousands upon thousands of eggs destined to be laid on cool and warm nights over three or four summer months.

Natural selection has created the intrinsic survival skills necessary to equip an apparently dull and insignificant sea turtle with the ability to use its ocean environment as a transport mechanism and a highway offering voyages of unimaginable challenges and excitement. This animal, one of the world's great navigators, once adult, faces few dangers other than large sharks, and its solid carapace is often sufficient to dissuade even them.

Little, however, could have equipped the turtles for the unequal struggle with man. Millions of turtles have died over the past four centuries as humans across the world killed them for food and sale with no thought for the future. Extinction loomed close for most groups and snuffed out some populations. But humankind has a unique characteristic, for the voraciousness is offset by compassion and an under-used talent - foresight.

Both have been employed with growing enthusiasm by South Africans over the past 33 years, during which time the protection offered by the Natal Parks Board has seen the number of nesting females grow substantially. The deep satisfaction from witnessing this great event in the natural history calendar has spilled over from the scientific community into the world of tourism, and now hundreds of visitors each year pay homage to nesting rituals that form the link between thousands of generations of this humble creature.

It is perhaps ironic that one of the longest migrations of loggerheads ever recorded in the world was female BB288 killed in Somalia in 1995 by the 'Restored Hope Fishing Company'. The laboured and quaint English used by the barely literate fisherman who took the trouble to write to the return address on the titanium tag, was touching in its description ...
'We captured a sea tortoise in profundity of 45 metres in sea bed and during the sloshing and decomposing of the animals we founded a metal label with flowing address written on it ...'

Such interest, plus the compassion displayed by an entire generation of South Africans, has ensured that the Maputaland turtles have indeed reach a stage of 'restored hope'.

To see a turtle nesting
Every summer hundreds of visitors to Sodwana Bay, Kosi Bay and Rocktail Bay either walk the beaches at night guided by local amaThonga people trained by the Natal Parks Board, or are driven on the beaches south of Mabibi by Parks Board guides to see turtles nesting.

That this important ecotourism opportunity exists, points to a conservation success equal to any achieved in South Africa. Previously the eggs were dug up and eaten in their thousands and the leatherback population dwindled almost to extinction. During the 1966/7 nesting period, only five leatherback females were seen during the entire season; indeed, during the first 10 years of protection an average of only 21 females were seen each season.

The loggerhead turtle had fared a little better, but not much. In the sixties when their conservation got underway, fewer than 200 nesting females were noted each season.

After 33 years of protection, the average number of nesting leatherback females has risen to more than 90, with a record year for the entire protected area being 164 - a wonderful return to a healthy population, with numbers clearly growing as the years pass. The same period has also witnessed a significant growth in the number of loggerhead females coming ashore; currently some 500 nest annually within the Maputaland Marine Reserve, the largest marine conservation area in Africa.

To witness the return of these compelling marine wanderers is an emotional experience, and it is not limited to scientists and their helpers. During this past season one visitor, witnessing a heavily breathing leatherback laying eggs in a ritual that is millions of years old, burst into tears, overcome by the moment she was privileged to be sharing.

The warm-blooded reptile
It takes each female leatherback 9-10 days to mature a clutch of eggs before laying. This is known with certainty as leatherbacks are unique among all other sea turtles - indeed, unique among all reptiles - because they can maintain a constant body temperature of around 30 ûC. The heat is generated by the energy used in fuelling the huge muscles that drive the flippers. Heat loss is prevented by a layer of fat, oil-saturated bones and efficient heat exchangers at the base of each flipper.

The animal's vascular system also plays a crucial role in thermo-regulation. Each of the turtle's arteries is totally surrounded by veins so that the heat from arterial blood is instantly transferred into the cold venous blood and carried back into the body. This unique attribute makes the leatherback lord of all the sea turtles as no other reptile species has displayed the ability to visit virtually every corner of the oceans of the world.

Too cold for girls ... too warm for boys
Sea turtles (in common with many other reptiles) have their sexes determined by temperature. There is a pivotal temperature (+/- 29.6 ûC) which, if not reached during the third week of incubation will produce only males and, if exceeded, will produce all females (crocodiles, incidentally, are the other way round!). This particular trait in sea turtles makes them very vulnerable to any rapid increase in global temperatures as a result of the greenhouse effect, as it is unlikely that this conservative species could alter their loyalty to nesting grounds fast enough to adapt to the changes in water temperature. Although loggerheads would, because of their widespread coastal nesting distribution, be minimally affected, the more tropical species, such as the green turtle Chelonia mydas, locked into island nesting sites, do not have such privileged flexibility and could conceivably head towards a female extinction.

The turtle's on-board compass
When loggerhead turtle hatchlings swim into the warm embrace of the Indian Ocean off Maputaland, they carry a geomagnetic fix in their brains, possibly locked into place during the eight-week development phase in the nest, or possibly imprinted in the first few frantic hours of heading out to sea. Years later, this mechanism allows mature turtles to navigate using the lines of magnetic force that surround the earth and return with remarkable accuracy to their natal beaches from north or south, and from all around Madagascar across the Mozambique Channel.

In other species, such as the leatherback turtles, this amazing technique enables them to navigate across thousands of kilometres of open ocean to reach the beaches of their birth.

Nature Reading
Cheetahs
Born to be Wild
Leatherbacks and Loggerheads
Giraffes in Africa
Rhinos in Africa
African Trees
River Horses: Hippopotamus
Marine Marvels of Maputaland
Survival Strategies of African Butterflies
Whale and Dolphin Watching
Great White Sharks near Capetown, South Africa
Run Sardine Run!