The fascinating life of the turtle

The physiological design and biological adaptations of sea turtles have remained unchanged for millions of years. There are certain aspects of their natural history that set them far apart from most marine inhabitants.

Yet all marine turtles share similar life histories, varying only slightly between one species and another. A quick look at their life history indicates just how complex their evolution has been, over their 200 million years on Earth.

The turtle’s life cycle

When physiologically ready, turtles migrate from distant feeding grounds to established nesting areas, where males and females mate for one to two months. After mating, females take two to four weeks to emerge on the beach to lay their first clutch of eggs. They may return up to eight more times to lay again in the same season, but four or five times is the norm.

Each nest contains around 100 eggs, which take about 60 days to incubate. The eggs only hatch after dark, when the sand surface cools. The hatchlings have to fight their way up through the sand for two or three days before emerging. Then they crawl down the beach and straight into the sea, using light, wave direction and the Earth’s magnetic fields for guidance.

They swim frenziedly for one day to get as far offshore as possible, then for a few more as a safety measure. For several years, they simply float like plankton on the ocean's surface before migrating from oceanic waters to shallow feeding grounds. These years at sea are typically called the ‘lost years’ because this is when scientists are least able to study them.

Between the ages of five to 10 years, the juvenile turtles grow some 20 - 40 cm in length. They remain at their feeding grounds for five to 10 years or more, until they reach sexual maturity when they first migrate as adults to the mating and nesting areas. This final part of the cycle is then repeated.

Illustration of a typical marine turtle’s life cycle:

An in-depth look at migration

The turtle’s periodic migrations to and from its nesting and foraging sites, sometimes over vast distances, is a source of fascination to biologists.

The green turtle has been known to swim up to 44 km in a single day, migrating as far as 3410 km, from Micronesia to the Marshall Islands. Some Omani turtles have swum to Qatar, and some Emirati turtles have gone over to Pakistan. Adult females do not necessarily nest at the closest rookery to the feeding area; sometimes they make very deliberate journeys to specific geographical targets much further away.

While some females have been seen to remigrate to a favoured site as long as four years later, many turtles nest only once in a lifetime. The turtles which do remigrate have been found to nest more frequently in a season and lay more eggs than first time nesters. This suggests there is some sort of adaptive mechanism or learning process directly linked to the first nesting experience. For instance, a bad nesting experience, where a female is disturbed while nesting or attacked near the nesting beaches, may be a contributing factor that decides whether she ever nests again.

How mature is a mature turtle?

Marine turtles can live extremely long lives; some live up to 80 years. It takes 15-35 years to reach sexual maturity depending on species, which presents unique challenges not only to turtle conservationists but also the turtles survival as a species as it takes such a long time before they are able to reproduce.

Hatchlings emerging today might only return to nest after 15 to 35 years, which obviously makes it difficult to chart their progress and estimate their ages with total accuracy. Factors which could have a massive impact upon the long-term survival of a group of turtles, such as intensive egg collection or adult harvesting, might not become apparent to observers for a number of years, if ever.

Why do they need conserving?

Sea turtles and their products have been used by mankind for thousands of years as a basis for food and a host of other uses. Today, they play a valuable role in non-consumptive uses such as tourism, education and research activities. They are also irreplaceable ecological resources as they function as key individuals in a number of habitats and can be an accurate indicator of the general state of health of their environment.

Turtles also have immeasurable value as cultural assets and play an important part in the traditional lifestyles and beliefs of many coastal people. They can be adopted as flagship species for conservation programmes, and because the conservation of turtles and their habitats addresses vast and diverse marine areas, they indirectly protect the complex and interconnected world on which human societies depend.

Why is the turtle’s plight unique?

There is an urgent need for immediate but carefully considered action to address the decline of turtles in the Gulf region and beyond. In planning this action, we need to bear in mind some unique factors:

Today we understand more about the turtle’s biology than ever before: while it was once thought that turtles come back to nest each year, it is now known they only return every three or four years and while it was once thought turtles matured in five or six years, we now know that this period can be much longer.

Our new understanding of these timescales presents us with unique management challenges. Simple fishery-style closures or seasons might benefit other species but they simply do not help turtles, as they take such a long time - literally generations - to mature and replenish themselves.

Coupled with this are ever-increasing demands on the turtle population; demands which are already impossible to sustain. Two hundred years ago, a small village would need to harvest no more than one or two turtles a month as the meat could be shared among family and villagers. Traditional boats and fishing gear likely limited the catch to a single adult turtle per outing however today those village fishermen have larger boats with outboard motors, access to wider markets through a developed road network and refrigeration to keep their product fresh. Harvesting is no longer a matter of subsistence: it is a commercial venture, satisfying the demands for meat and an ever-expanding trade.