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Auteur Topic: Proyecto Todos Tortugueros Dermochelys coriacea ( Leatherback )  (gelezen 4414 keer)

Berichten: 2797

« Gepost op: 7 April 2009, 20:18:41 »

Bedankt Jim en Ellie Pickel voor de info. en foto's en jullie vriendelijkheid.
Erg leuk om julie ervaringen te zien en lezen wat betreft het beschermen en laten uitkomen van de eieren van de Dermochelys coriacea.
Fantastisch mooi werk om te doen en we wensen jullie veel succes met het beschermings projekt.

Jim en Ellie, ga zo door uitroep ! uitroep ! uitroep ! team

The Baja California peninsula is home to five of the seven species of the world’s marine turtle. Among them, all considered endangered or threatened, the leatherback turtle (Dermochelys coriacea) has been on the endangered species list since the 1970s. Naturally high mortality combined with human disturbance has reduced the number of these reptiles by 97% in the last three decades, reducing the Pacific Ocean’s female population from 115,000 in 1982 to an approximate 3,000 today (Phillips). This dramatic decrease in numbers has positioned Dermochelys coriacea as the world’s most endangered marine turtle. Local NGOs and communities have been working together, occasionally with the support of local governments, to preserve the last remaining leatherback turtles.

Dermochelys coriacea is the largest among marine turtles. A mere 2-1/2 inches long at birth, leatherbacks can reach10 feet in length and weigh up to 2000 pounds (Lyons). The leatherback hatchling is easily recognizable thanks to its massive dark oval-shaped carapace, marked by 7 white stripes that run along the length of the shell. Studies have shown that leatherback turtles can travel a great distance and have been found in Arctic water at a latitude of 70 degrees North. They are present in most of the world’s oceans, nesting on beaches on the Atlantic, Pacific and Indian Oceans (Lyons). The Pacific population’s feeding and nesting grounds are loosely located between the Tropic of Cancer and Tropic of Capricorn.

The leatherbacks of the Pacific nests between the months of October and March. Females begin reproducing at 7-15 years of age, reproducing every 2 to 3 years. During a fertile year, the female leatherback lays her eggs 5-7 times at a 10 day intervals. The female deposits between 40 and 120 eggs in a meter deep nest located above the tide line on sandy beaches. The temperature experienced by the embryo during the middle third of development will determine the sex of the offspring. Results may vary according to the location, but eggs incubated at a temperature below 29 degree Celcius typically produce only males and above 30 degrees only females are expected to hatch (Binkley et al.). However, the eggs exposed to temperatures lower than 25 degrees and above 35 will not develop (Lyons). The incubation period varies, but it averages at about 60 days. Of all the eggs deposited, according to estimates, only 1 in 1,000 individuals will reach reproductive age (The Leatherback Trust).

There are several causes for the high mortality rate that has determined the drastic population decrease among leatherbacks (and other marine turtles) of the last few decades. Leatherbacks, like other marine turtles, have few natural enemies. While in the water their ability swim fast and to dive to a depth of 4,000 feet, makes them hard to catch by natural predators, such as sharks. When on the shore to deposit eggs, however, they can fall victims of jaguars and other large predators. The dangers for the hatchlings are far more numerous: 1)the nests can be located too close to the tideline and can be washed away by waves, 2) the temperature may be too high or low for proper incubation, 3) coyotes and wild dogs can dig into the nests and consume the eggs, 4) the young hatchlings have to cover an average distance of 10 meters to the relative safety of the ocean, where they often fall prey of seabirds and crabs, 5) once in the ocean they can easily become pray of fish. These non-human predators and causes of death further reduce the survival rate of hatchlings.

But the major threat is posed by humans. Whether directly or as a byproduct of their behavior, human actions have affected leatherback in major ways an brought them to the brink of extinction. The major cause of mortality is represented by commercial fishing. The strong nylon lines of gillnets and long lines used to catch large fish can strangle or drown a leatherback in a matter of hours. Leatherback also are victims of pollution. Plastic bags, pellets and Styrofoam can be mistaken for jelly fish and ingested by turtles. The plastic tangled in the intestines can obstruct the gut, lead to absorption of toxins and reduce the absorption of nutrients from real food (Turtle Trax). This process can eventually cause death. In addition, many turtles are still caught for human consumption in many parts of the world. The dangers a leatherback faces, however begin long before the hatchlings reach the ocean waters from their nests.

On the ground, the biggest danger faced by the leatherback is posed by eggs poachers. A traditional delicacy of many coastal populations in Central and South America, turtles eggs are poached by the hundreds of thousand despite bans imposed by local governments. In areas where local communities are unable to maintain a stricter patrol over their beaches during the nesting season, the threat of habitat loss due to coastal development is often very serious. Finally, recent studies (Deem et al.) have also demonstrated the danger of light pollution. Both hatchling and adult leatherbacks are naturally attracted by light. Artificial lighting created by human development can cause disorientation and misorientation. In Gabon (currently the largest nesting site in the world) both adult leatherback and hatchlings have been found in the interior savanna heading in the direction of city developments. Growing concern is also directed at the threat of climate change. A very strong female biased-sex ratio has been observed on multiple nesting sites raising concern over the necessity of higher gene flow (Binkley et al.).

Playa Grande, in Costa Rica, is the fourth largest leatherback nesting site in the world and the largest in the Pacific. For this reason, this site has been for many years a good indicator of the status of the leatherback. In the early 1980s scientists at Playa Grande would identify around 200 turtles a night during the nesting season, today they may spot 15 in a good night (Miller-Davenport). The nesting has decreased from a few thousand just ten years ago to fewer than 100 in the past five years (Leatherbacks). This beach is now protected as part of the Parque Marino Las Baulas. There are not yet signs of population recovery, but thanks to the conservation efforts the number of hatchlings has been maintained relatively high considered the diminished number of nesting females (Tomillo). Due to the slow development of this marine turtle, positive effects on the local population may be seen only in future years. Similar conservation efforts are underway in other parts of the words as well.

Todos Santos is a small fishing town located in Baja California Sur on the Pacific Ocean. The town lies on the Tropic of Cancer, this imaginary line also marks the Northernmost nesting site for leatherbacks in the Pacific Ocean. Due to its latitude the temperatures at this site are often low compared to other Mexican and Central American sites. For this reason, the embryos in the nests laid after the beginning of November will likely not receive enough heat to properly develop as the outside temperatures decrease from early January through June. Without the intervention of conservation groups and the use of hatcheries most nests would be entirely lost. While the temperature issue can be relatively easily overcome with the help of “nurseries”, other serious problems affect the area.

All conservation groups present at the annual Convention on Marine Turtles held in Loreto in February 2009, reported that the biggest threat faced by leatherbacks and other turtles along the Baja California coast (Pacific and Sea of Cortez side) is posed by long-line fishing. It is estimated that 50,000 leatherbacks end up every year as by-catch of commercial fishing boats. Egg poaching was cited as the second biggest problem faced by leatherbacks, followed by coastal development and habitat loss, plastic debris ingestion and “beach traffic”– the compression of the sand created by heavy vehicles (ATVs and USVs) driving on the beach and dunes make it impossible for the hatchlings to dig their way up to the surface. All these challenges are present in various capacity in the Todos Santos area.

To address these and other issues members of the Todos Santos community have established a non-profit organization in 2004. Working in collaboration with ASUPMATOMA (The Association for the Protection of the Environment and the Marine Turtle in Southern Baja), and ProPeninsula, Proyecto Todos Tortugueros aims at replenishing the population of local sea turtles. For the 2008-09 nesting season, the Todos Tortuguero Group has for the first time obtained permission from the Federal Government to build an invernadero(nursery) on the beach of Las Playitas, about 10 km North of town. The species present at the invernadero are leatherback andLepidochelys olivacea (Olive Ridley). Between October 2008 and March 10th, 2009 12 leatherback nest were found and number of eggs collected totals at 866. The invernadero also contains 16 Olive Ridley nests. The first leatherback nest hatched on January 23rd after a 76 day incubation. To this day 204 leatherback hatchlings have been released. The data for the previous three seasons is as follows:

Nesting Season  2005-2006  2006-2007  2007-2008 
Nests ========  12 ======  1=======  0 
Eggs ======== 696 =====  54 =======  0 
Released =====  555 ===== 22  ======= 0 

To facilitate the success the group is experiencing this year, volunteers and employees of the Todos Tortugueros group have performed night patrols of the beaches when a leatherback is scheduled to come ashore to deposit eggs. When a female is spotted, she is only approached after she has laid the eggs to avoid imposing a threat to her. With special care and attention the eggs can be collected as she is laying them just by positioning a bag underneath her, above the hole she has dug. After the eggs are laid, the turtle is checked for tags or microchips and she is tagged if no tags are present. She is measured and the head is photographed since it displays a clear mark on her forehead that distinguishes her from all other leatherbacks. When the nesting turtle succeeds in eluding the researchers’ efforts to find her at night, the eggs are carefully collected in the early mornings when the easily recognizable tacks are spotted by local fisherman who promptly alert the group. Finding the eggs requires the involvement of several people and sometimes several hours, since it is not always apparent where the nest is located underneath the maze of tracks left by the mother. Local rancheros often help digging, collecting and transferring the eggs from the nesting site to the invernadero.

The partnership with the local community is of vital importance for the survival of this species. Extensive education programs have been taking place in this area, like in many others in the region. Rancheros leaving in the proximity of Las Payitas have accepted with enthusiasm their new roles as protectors of this endangered species. Former egg poachers have become crusaders for the wellbeing of leatherbacks and other marine turtles. During the heights of the nesting season they participate in the night patrolling of the beaches and eggs relocation. At the same time, an experimental environmental curriculum (the “Todos Biologos” initiative) created by a group of mainly American expatriates has been in place in local schools for the last four years and aims at instructing a new generation on the dangers of land and ocean waters mismanagement. In the classrooms, guest speakers address environmental issues, especially pollution, trash and the plight of marine turtles to an audience of children aged six through 13. On the grounds of a primary school in Todos Santos, a new recycling program for plastic, glass and cans has been established, and allows children to witness and participate in the sorting and packing of recyclable materials.

Despite the Todos Tortugueros and similar groups’ efforts however, the problem is still far from being solved. The numbers of the remaining leatherbacks remain dangerously low and thousands still die every year as incidental by-catch. In 2004 at the 24th Annual Symposium on Sea Turtle Conservation and Biology, held in San Jose, Costa Rica, it was announced that if the current trends continue, the leatherback may go extinct within 10 years (Phillips). Todos Santos is also facing the relatively new challenge of coastal development which leads to habitat loss and deterioration of local beaches. The Todos Santos community has for decades tried to protect the dunes and the unique coastal habitat, however in recent years unscrupulous developers started selling lots on the dunes for a lucrative return, at the expense of the marine turtles. While there has not been any recording of hatchlings being disoriented by lights, Todos Santos is, for better or for worse, a growing town, and the issue could become serious in the next few years.

The involvement of the community is paramount to the success of this and any other environmental fight. But the community will hardly succeed if it doesn’t have the support from the local government. The Todos Tortugueros group depends on the willingness of local government agencies to issue permits to build nurseries, patrol beaches and to exist as a non-profit organization. The issuance of permits is of great concern for the group’s officials since conflicting and personal interests within and between agencies are always present. Leatherback turtles are protected by international treaties and agreements as well as national laws. They are listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) which forbids any international trade in leatherbacks, their eggs, or products derived from them.

In Mexico, the “distressingly high level of poaching” recorded by Binckley (742) in the early 1980s has been reduced by laws to protect the leatherback. Full protection was granted to them in 1990 (Crouse). Federal agents are in charge of patrolling beaches and highways in search of poachers. However, the application and enforcement of these laws is, in the opinion of the author, doubtful. At a bottom-up level, the Todos Santos community has responded well to the call for a solution, but some skepticism still exist and can undermine any well meaning operation. Some people still believe it is a person’s right to harvest marine turtles’ eggs because it is part of the local tradition. Others think that nurseries should not be built and the turtles should be left to their own fate. Their fate is, unfortunately, dependent upon to the protection of beach habitat and the reduction of fishery bycatch. This is why it is important that groups like Todos Tortugueros focus on local communities and individuals to conserve their environments by expanding knowledge and developing new solutions.

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