WiLD Blog

Marine turtles almost always return to the same beach to lay their eggs. The egg-laying sites are often far from the feeding areas and the females cross several hundred kilometers of ocean with no visual landmarks. How do they manage to return to the same spot?

A study by Simon Benhamou of the Center for Functional and Evolutionary Ecology at Montpellier, France, together with other groups, shows that the marine turtles use a relatively simple navigation system involving the earth’s magnetic field, and this allows them to return to the same egg-laying site without having the ability to correct for the deflection of ocean currents. This work, published in Current Biology and Marine Ecology Progress Series, should allow better conservation strategies for this endangered species.

Every 4 years, on average, Indian Ocean green turtles (Chelonia mydas) travel hundreds of kilometers to specific egg-laying areas, where they will lay 4 to 6 successive clutches. To better understand the navigation process and the sensory channels involved in this long-distance oceanic travel, the researchers have conducted a multidisciplinary study, involving biology and physical oceanography, in two series of experiments. In the Mozambique Channel, between the east coast of Africa and Madagascar, on the beaches of the French Islands of Europa and Mayotte, they caught turtles at the beginning of their egg-laying cycle, so that the animals were strongly impelled to return to this area to complete their cycle. After having Argos transmitters fitted to their shells in order to satellite track their return journey to the beach, the animals were released in open sea, several hundred kilometers from the egg-laying site.

The first experiment was to study the navigation system of the marine turtles and discover how they detect the ocean currents: are the turtles’ movements controlled by the currents or can they use them to their benefit? The study has shown that the marine turtles’ navigation system allows them to maintain their course towards the egg-laying site wherever they find themselves. It is almost as if they were equipped with a compass pointing towards the beach in question. So they can correct any deflection they are subject to: transport by boat, ocean currents… But, unlike human navigators, they are not able to correct for ocean drift in plotting their course. So the movements recorded by the satellite are a combination of deliberate action by the turtles and the effect of currents. So it appears that the turtles’ navigation system is relatively simple and may cause them to be wander at sea for long periods during adverse ocean conditions. One turtle released 250 km from its egg-laying site on Europa traveled more than 3 500 km in two months before returning there!

In the second experiment, the researchers have studied the effect of the earth’s magnetic field on the turtles’ navigation system. They have shown, for the first time in natura, that marine turtles use the magnetic field of the earth to orientate themselves. When this field is disturbed by placing a powerful magnet on their heads, turtle navigation is not as good. But the fact that they can still return to their original egg-laying site shows that the geomagnetic field is not the only information source that they use. Researchers think the turtles may also use their sense of smell like certain sea birds or homing pigeons. This hypothesis remains to be proven…

This work should improve conservation strategies for marine turtles, an endangered, officially protected species, by providing a better understanding of how they manage these long migrations between egg-laying and feeding areas.

Note: This story has been adapted from material provided by CNRS.  http://www.wetsand.com

posted by jose E. lopez

now these days sea turtles face a far more greater danger other than extinction, Pollution; companies dumping toxic waste in the earth’s oceans forces marine life to change their habitats and find new places to live which involve bitter conditions and unsuitabe places for marine species. Our governments should try to put an end to this and regulate the oil companies to stop this act of violence against our world.

A study released says that coral reefs in the Pacific Ocean are dying faster than previously though. In the past two decades 20 percent of coral has disappeared from the Pacific Ocean. More than 600 square miles of coral reefs has disappeared since the 60’s. Losses in well-protected areas such as the Great Barrier Reef were just as bad as losses in poorly managed areas like the Philippines. The United Nations estimates that nearly a third of all coral has been lost and by 2030 an estimated 60 percent of coral cover will be gone.

There are many reasons behind the decline of coral reefs. Global climate change, storm damage, agricultural runoff, predators and diseases are the main factors influencing this rapid decline. Warming waters cause coral to “bleach” and lose their color, often resulting in death or reduced reproduction. In addition the ocean absorbs carbon from the atmosphere, which causes the ocean to become more acidic and thus dissolving the coral’s calcium skeleton. Agricultural runoff dumps massive amounts of nutrients into the ocean, fueling massive algae blooms that block out light for coral. Overfishing has exacerbated this problem, since no predators are left to feed on algal blooms.

Coral reefs are dying at an unprecedented rate around the world.

It’s so hard to describe how disheartening this news is to me.

Coral reefs are a source of life for people. Ecotourism and fishing provide money for families to make a living. Coral reef islands are homes for people as they have been for hundred of years. They’re homes to an amazingly diverse group of animals and plants. They’re also a source of amazement and joy to the people that visit them.

I stayed on a coral reef island for a few days when I studied abroad, and I will never forget the amazing things I saw. I was gathering algae for a research project during high tide on the reef and when I looked up I saw a sea turtle hovering in front of me, quietly contemplating me as I slowly reached out and scratched it shell (I’ve been told that sea turtles enjoy having the algae scratched off their shells by divers). I’ve seen eagle rays jump six feet out of the water and silently watched female sea turtles digging nests on the beach. I’ve seen a 600-pound grouper hunting at night and swam beside a five-foot shark. I’ve seen a giant clam the size of a small child and dove through a school of simmering fish. Just floating above the reef and watching the sheer abundance of life weave their way around you as they go about living is indescribable.

I’m unable to do justice to all the crazy things I saw. I’m just telling stories. There are so many things I can’t convey in words. It’s the difference between seeing it on the TV screen and actually experiencing the realness of it. I think there was a point where I just stopped and thought, “This is real”. Before, all I’ve ever seen of the reef was in National Geographic and nature shows I watched as a kid. It’s unbelievable to think that someday, the only things left of coral reefs will be stories, pictures, movies and memories. One day, people won’t be able to go out and see all these things anymore, simply because the reefs will one day cease to exist. They’re already on their way there.

I’ve read too many reports and seen too many news stories on disappearing reefs. Whenever I see another one, all I can think to myself is, “This is unreal.”

Calvin Lee

A big thanks to Fay Crevoshay and Aida Navarro and of course our gran amigo Jorge Campos for launching this spectacular campaign today in Acapulco with the heroic sea turtle defenders of Mexico. Serge 

INTERNATIONAL HERALD TRIBUNE 

Jorge Campos launches campaign to save marine turtles
 The Associated Press

Published: October 27, 2006
ACAPULCO, Mexico. Mexico’s former star soccer player Jorge Campos, teaming up with environmentalists in this Pacific coast resort, launched a campaign Friday to protect Mexico’s endangered marine turtles.
 
 Campos, who was the assitant coach for Mexico’s 2006 World Cup team, called on President-elect Felipe Calderon, who takes office Dec. 1, to dedicate more resources to protect marine turtles along the coast of Guerrero state, where Acapulco is located.
 
 ”Turtles are worth more alive than dead,” he said, adding that the turtles could draw millions of tourists to the region.
 
 Mexico is a major nesting area for several species of sea turtles, which are protected by law. Harvesting or selling their eggs is a criminal offense, punishable by up to nine years in prison and fines.
 
 Still each year, officials seize thousands of turtle eggs at Mexican markets. The eggs are considered a delicacy.
 
 Fewer than 1,000 adult female leatherback turtles are left in Mexico’s Pacific range, down from an estimated 70,000 to 90,000 in 1980, according to the World Wildlife Fund.