Ancient reptiles of the deep, sea turtles have long been surrounded by mystery and ignorance. Now as a result of much research by dedicated scientists and conservationists, our knowledge of these puzzling wild creatures is expanding. Experts believe that obtaining a complete picture of a turtle’s life cycle may be the key to saving them from extinction.

Aerial view of unusual aggregation of thousands of Green sea turtles Chelonis mydas waiting in the waters of Raine Island until night fall when they will swim ashore and lay their eggs (bottom right). Every dot represents a turtle - to see larger version, please register on the Oceanwide Images website.

Green turtles were heavily exploited in the 1920’s for turtle soup by canneries on Heron and North-West Islands off central Queensland. Around a thousand nesting female turtles were harvested each year from North-West alone, almost resulting in the total decimation of that island’s breeding population. In other parts of the world such as the Cayman Islands, Bermuda and the Dry Tortugas, entire populations have become extinct through commercial exploitation by man.

Of the seven existing species of sea turtle, six are today listed as threatened or endangered. In 1950, green turtles became protected in Queensland and in 1968 this legislation extended to include all turtle species.

This summer from November through March, the many conservationists and volunteers of the Queensland Sea Turtle Project will make their annual pilgrimage to the rookeries of Mon Repos and the Capricorn-Bunker Islands. Here they will carry out important research into turtle biology, which may bring us closer to understanding their obscure and perplexing life cycle. Every night these beaches will be patrolled by the researchers along with many tourists and interested onlookers who hope to witness the awesome event of a female turtle coming up to nest.

Nesting female Green sea turtle Chelonis mydas returning to sea after nesting

Sea turtles take many years to grow to maturity. It is thought that a female turtle is around fifty years old when she begins to mate and breed. When her first breeding season finally comes around, she drags herself up onto the beach, digs first a body pit and then an egg chamber of around 50cm depth and lays an average of 50 to 130 ping-pong ball sized eggs depending on the species. Over the course of that one season she may repeat the procedure up to eight times, laying a total of 500-1000 eggs. Of these maybe one or two will reach adulthood. Her nesting season complete, the female will probably not mate again for another three to six years.

Green sea turtle hatchling Chelonis mydas emerging from sand making way to the sea.

The turtle eggs incubate in the sand for around seven weeks during which time the embryos develop into miniature turtles of 4 to 6 cm in length. Recent studies have uncovered some astonishing facts about embryonic turtles. The nest is in fact a complete micro-environment where factors such as temperature, sand type, moisture and position on the beach will affect the outcome of the eggs. The sex of a turtle is not genetically determined at conception. When the eggs are laid, the embryos within are sexless and whether they turn out to be male or female depends entirely on the temperature of the sand around the nest. If the sand is 27 degrees Celsius or cooler there will be more males and if it is over 30 degrees, females will predominate. Thus, some beaches produce greater numbers of one sex than others. Though most of the eggs will develop into healthy baby turtles, some will fall victim to crabs and infestation by fungus.

When the baby turtles hatch they spend a few days in the sand, gradually making their way to the surface and when the time is right (usually at night) they emerge together and make an energetic dash down to the water. It is by some innate sense that these tiny creatures, which look something like wind-up bath toys, know exactly in which direction the sea lies, even when it is obscured by ridges or walls. They instinctively move toward the brightest light source, which is normally the light area on the horizon. They can be disorientated by artificial light, however, so every effort is made at rookeries to educate the public about the distraction unnecessary lights may cause. At least 90% of the hatchlings will escape birds and crabs to successfully reach the water, but it is here in the sea that their journey becomes perilous. The helpless little turtles are very easy prey to many reef fish and sharks and most will not make it across the reef flat.

Green sea turtle hatchling Chelonis mydas swimming in ocean

When a newly hatched turtle leaves its natal beach it is unlikely to be seen again until it reaches around 30 cm in length and an estimated age of ten to fifteen years. Where these young turtles spend the early part of their lives is a complete mystery, though it is speculated that they drift with ocean currents for great distances and remain in the open ocean until they reach a certain level of maturity.

Many scientists and volunteers will dedicate many nights this summer to observing sea turtles on Queensland beaches. The work they do is painstaking and often tedious and they must brave all weather conditions. The majority of people working for the Queensland Sea Turtle Project are unpaid volunteers and it is only through the tireless efforts of these people that we hopefully may be able to learn enough about sea turtles to procure a safe future for them.

Text: Sandra Eugarde
Photography: Gary Bell