Distinguishing Features
Marine turtles are instantly recognisable by their large, streamlined shell and (unlike their land-based cousins) by their non-retractable head and limbs. Front flippers are used primarily for propulsion through the water while hind flippers act as stabilising rudders.
Depending on species, colouration may be olive-green, yellow, greenish-brown, or black. Interestingly Green Turtles are so-called because of the colour of their body fat rather than their external appearance.
So how do you tell them apart? Well there are numerous differences between the species but as an introduction let's just look at one way you can identify which is which.
A Green Turtle is easily distinguished from others because it has a single pair of pre-frontal scales (scales in front of the eyes), rather than 2 pairs as the other family members have.
Olive Ridleys are olive in colour and look out for the 2 pairs of pre-frontal scales and the standard mouth shape.
A Hawksbill has a narrow head with jaws meeting at an acute angle and with its upper jaw protruding out and curving slightly down much like the bill of a hawk, funnily enough.
The Leatherback Turtle should be reasonably easy to spot due either to its sheer size or by the prominent longitudinal ridges of cartilage running the length of its shell.
Loggerheads are one of the largest species of turtles with the reddish-brown carapace of an adult averaging just under 1m in length. The name derives from their large, heavy-set head and short neck.
Size differs with species, Olive Ridleys being the smallest at around 60 cms in length and weighing around 45 kgs when fully mature. Leatherbacks on the other hand can grow to as much as 1.9 metres in length and have been known to weigh in at a whopping 916 kg!Feeding habits
The vegetarian diet of the Green Turtle consists mostly of algae and sea grass. Olive Ridleys use their powerful jaws to crunch through the exoskeletons of crabs and molluscs. Soft-bodied animals such as jellyfish, squids and tunicates are also eaten by Olive Ridleys as well as by Hawksbills and Leatherbacks.
Due to features such as powerful jaws for crushing or scissor-like jaws for cutting soft flesh, you would be well advised not to poke around near the mouths of any turtle, at least, not if you value your fingers!Reproduction
Mating time usually occurs several weeks before nesting season at a time when the company of females is a much sought-after prize. Several males may court a single female and it is a common diving sight to see a mating couple being rudely jostled by 1 or more males who want in on the action. At times like these it helps a mating male to keep such unwelcome interlopers at bay by clinging firmly to the female with claws on the front flippers which secure the passionate embrace.
Copulation is internal and several weeks later the females come ashore to nest. Turtles dig their nests in the sand using their hind flippers to create a pit for the eggs. Then 1 by 1 she plops out the slimy, delicate-shelled, ping pong ball-like eggs into the hole before covering the nest over with sand.
This can be repeated several times a season and, through an incredible sperm storage system within the female's oviducts, she may be able to lay several clutches without having to go through the nasty business of mating again. Neat, hey!Life cycle
When they emerge from their nests the little hatchlings make instinctively for the water guided most probably by the light of the moon. This explains how on beaches with strong unnatural light, the little turtles often find themselves heading for the nearest bar rather than the sea.
For the first few years after hatching, the young disappear. No one has seen a juvenile Pacific Turtle in the wild. Recently, the mystery was finally solved in the Atlantic when juveniles were found living in and around floating sargassum weed feeding on all the small animals that seek shelter there. There has yet to be recorded such a similar sighting in the Pacific.
At long last, when the turtle has fully matured, it will return to the beach of its birth and the cycle of mating, laying eggs, babies hatching and running for their lives, will be repeated all over again.Predation
The vast majority of hatchlings will, of course, die young, falling prey to seabirds, crabs and hungry fish. Those that do make it will remain solitary until they too feel the urge to mate.
Those that negotiate the difficult early years and make it to adulthood encounter few predators, mostly large sharks in particular tiger sharks.Distribution
All but the Leatherback are found predominantly in coastal areas. Leatherbacks are highly oceanic and venture into shallower water only for breeding purposes.
All of the 4 species featured here can be found when diving in the Indo-Pacific region. Other types are indigenous to specific areas, for example the Black Turtle in the Americas and the Flatback in Australian waters.Ecological Considerations
Very few other creatures are as symbolic to marine conservation efforts as the sea turtle.
In the Soup...
Loss of breeding grounds due to beach development is a particular concern given that some beaches which once witnessed thousands of turtles coming ashore to lay their eggs now see but a few. Human development, bright lights, rubbish and activity can all discourage females from nesting.
Discarded flotsam, such as plastic bags, are often mistaken by turtles as jellyfish with deadly consequences. Shrimp nets and other fishing apparatus also account for great numbers that become entangled and, just like we would, run out of air and drown.
However deaths at the hands of humans are not always accidental. Turtle meat and soup is still widely available in many parts of the world including Bali, and their eggs are considered an aphrodisiac in certain cultures. The shells are also highly prized for decorative purposes or to be transformed into items such mundane, functional items as combs and spectacles.
Protective Measures
Awareness of dwindling species numbers has lead to measures being taken throughout the world to allow them to nest in peace. The "Convention on International Trade in Endangered Species" (CITES) controls international trade in endangered and threatened species. Sea turtles are covered under Appendix I of this agreement and receive protection from international trade by all countries that have signed the treaty.
On a local scale the dive resorts
on Sipadan Island, for example, have been closed to tourists since January 2005 allowing an island which was previously full of nesting turtles to be given the chance to return to its former status.
Countless other resorts in such spots have accommodation raised on stilts to allow the turtles free movement. Many also adhere to strict rules regarding external lights at night and guests behaviour in relation to nesting.
However the intentional and accidental killing goes on for commercial reasons. Steps are being taken to reverse attitudes and trends in countries where the meat and products are considered exotic - but this will not happen overnight and as the saying goes 'when the buying stops the killing can too'.
Dwindling Populations
World-wide population numbers for sea turtle species do not exist and all figures you will find are based on estimates of the number of nesting females based on nesting beach monitoring reports and publications at varying times. As such it is difficult to state meaningful worldwide numbers.
However what is clear is that local population numbers all record declining populations across every species and the forecast for the future at current rates of killing is bleak. Although the CITES listing has slowed their decline, much more needs to be done to reverse attitudes and conserve them for generations to come.
