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The lifespan of turtles is probably similiar to humans, they may have to liuve to about 70 years of age.
Photo: Courtesy of Parks Australia Cocos (Keeling) Islands

September 13, 2002
The Lives of Sea Turtles - Part 2 - "Lifecycle"
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Log Transcript

This is Genevieve Johnson speaking to you from the Odyssey in the Seychelles.

In the last Odyssey log, Dr. Jeanne Mortimer discussed how sea turtles come to land in order to breed. Today, we learn more about the life cycle of sea turtles explore how they survive in the open ocean, where they go, and how long they stay at sea before returning to land.

Dr. Jeanne Mortimer:

Let me just run through the life cycle of a typical turtle; although there is no such thing as a typical turtle as they are all quite different. Research has shown that when young turtles or hatchlings go out to sea they have compass sense - meaning they can keep a course. Upon entering the sea for the first time, whatever direction they start swimming, they will maintain that course for several days; that carries them straight out to sea into deep water where they are safer. You don't normally think of deep water as being safe, but if you are a turtle, deeper is safer.

These little turtles tend to float and then they will get caught in currents and if you have been out at sea you will know that the sea is very blue. The water is clear and there is not much there, just water. You can imagine that if you are a small animal looking for food you could starve pretty quickly. The way turtles and many other animals are able to keep alive in the open sea is that they get caught in currents that bring together floating objects so you get these drift lines. These are areas where you have two currents coming together, often they are caused by wind and it concentrates all floating objects together. You have turtles, you have plants, you have turtle food and, also, turtle predators. It's a whole community of animals living together. These drift lines are attractive to birds that come down to feed on the little fishes, so it is really quite a complex community and that is where young turtles live. They will live in these areas for years, the first years of their lives are spent in the open ocean where they will float for thousands of miles and they can completely circulate entire ocean basins.

Young sea turtles float around in the deep ocean for years feeding at the surface where it is safer. Once they become adults, they move into shallower water and feed at the bottom.
Photo: Courtesy of Parks Australia Cocos (Keeling) Islands

We don't have a lot of information yet from the Indian Ocean, but we do have good information about Loggerhead turtles living in the Atlantic. What we know is that they start off from the coast of Florida, they get caught in these oceanic gyres and go all the way around throughout the entire Atlantic system, they even go as far as the Mediterranean. We know that Loggerhead turtles from Florida feed inside the Mediterranean and cover a huge area. Once they get to be a certain size their diet changes and something tells them they need to go somewhere else and they move into shallow waters. Green turtles and Hawksbills in the Indo-Pacific move into shallow waters at about 30 centimetres in shell size. Hawksbills tend to go to coral reef areas. Green turtles tend to go to sea grass areas, so instead of living in the deep sea and feeding near the surface, they now live in shallow water less then 20 - 30 meters and feed on the bottom. They will dive down and feed and then come to the surface for air as they are air breathers, and they will live this way for decades as they grow up.

Once they become an adult it seems, based on evidence we have from satellite tracking, they will come to the nesting grounds and then move back out to their feeding grounds which is probably the same for years and they will make this migration back and fourth.

Their life span is probably similar to humans, so a turtle may live to about 60 - 70 years, but we don't know how long they live after they stop breeding because a lot of our data is coming from turtles on the nesting beach. After they leave their nesting grounds and go off to their feeding grounds, they are in the deep sea and they are harder to study so we don't know exactly how long they live, they may sit in their turtle rocking chairs for another 20 - 30 years.

The natural predators for adult turtles are animals like sharks and some of your giant groupers. I know that here in Seychelles I have some fisherman friends that have caught groupers that have been 10 feet long, with turtles inside them, so they are a real threat to a good sized turtle. As far as sharks go, not all sharks will eat turtles, the main one that eats adult turtles is the tiger shark, and tiger sharks will definitely bite big turtles in half. But really aside from sharks and very big fish, once a turtle becomes an adult it has very few natural predators. The biggest problem turtles have has been people.

Genevieve Johnson:

Stay tuned for the next Odyssey log when Jeanne discusses the variety of problems turtles now face both on land and at sea as a result of human activity.

Log by Genevieve & Chris Johnson with Dr. Jeanne Mortimer

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