More of our class explores Lighthouse Cave, San Salvador, Bahamas.
Leatherback sea turtles are the largest living marine reptiles. Their shell length reaches 1.7 meters and their mass up to 700 kg. They live almost their entire lives at sea. Leatherbacks migrate hundreds of miles, across entire oceans every year and dive as deep as whales. The only times they are on land are when the female turtles return to their hatching beaches for about 1.5 hours to lay their eggs, and when hatchlings emerge from the nest and make their way to the ocean. Males on the other hand, never leave the ocean. Each female leatherback has the potential to nest up to ten times in one nesting season, and return every 3-4 years for as long as thirty years. No leatherback on the Pacific coast of Costa Rica, however, lives long enough to make this kind of contribution to her species. Most Pacific leatherbacks only nest once, because they are killed at sea.
It is estimated that the leatherback turtles are sexually mature when they are about 10 years old and may live to be 40 years old. Studying their biology is very difficult due to their sporadic visits to land, and the fact that male and young turtles are almost never seen at all. As a result, most studies and protection efforts have focused on the nesting females and hatchlings.
Due to the Leatherbacks’ soft, cartilaginous shell that differs from the usual hard bony one, they are different from other sea turtles. Their name “Leatherback” is derived from the actually appearance of the shell. Their more streamlined shape and larger flippers enable their migratory and pelagic lifestyle, as opposed to other sea turtles.
When the female turtles come ashore to nest, they tend to choose beaches which are generally free from rocks and have a gentle slope. The turtle emerges from the ocean at night, usually close to the high tide and crawls up the beach until she is above the high tide mark. There she selects a site free from wood, vegetation and other debris and digs a pit for her body by throwing sand with powerful strokes of her front flippers until her body sits in the hole she created.
With her rear flippers she then delicately digs out a chamber about 70 cm deep for the eggs. The sand must be of the right texture so that the nest cavity doesn't collapse while it is being dug. She alternates with her rear flippers to reach into the hole and scoop out the sand, which is then flicked to the side. When the hole has been dug as deep as the flippers will reach, she starts to lay her eggs.
During the period when the eggs are being laid, she becomes very unresponsive to her environment and this is typically when biological information is collected. About 70 large, fertile eggs and 40 small, infertile eggs are laid, some with yolks and some without. The function of the smaller eggs is not clear. The turtle then gently packs sand into the hole with her rear flippers and disguises the location of the nest by throwing more sand with her front flippers, possibly to hide the location of the nest from predators of the eggs.
When the nesting process is complete, she returns to the ocean for about 1.5 to 2 hours after she first emerged and takes no further part in the care of the eggs or hatchlings. Female turtles nest on average 7 times in the season, at intervals of about 9 days.
The incubation period takes approximately 60 days, and the temperature of the surrounding sand actually determines the sex of the hatchlings during a critical phase of their embryonic development. At Playa Grande, temperatures above 29.5 degrees Celsius produce female hatchlings, while below 29.5 Celsius the hatchlings are male. The hatchlings break out of their eggshells under the sand and begin to dig their way to the surface, to emerge in groups at night. “The crawl to the water is a dangerous time for the hatchlings, but it may also play an important role in allowing them to ‘fix’ the location of where they are, so the females can return to the same place to nest as adults” (www.leatherback.org/ldc/pg/aboutturtles.htm). There is very little information on what happens to the hatchlings after they enter the ocean, but very few survive to become adults. Some say only a few in a thousand live to see adulthood a year.
We know very little about the life of leatherback turtles after they leave the beach as hatchlings. We know that they appear to migrate long distances between feeding and nesting areas. Their main diet is jellyfish. Leatherbacks have special spiny structures in the esophagus to trap them there. They have amazing diving abilities and are able to dive below 1400 meters and remain submerged for nearly an hour. Useful information is being gained by satellite tracking of adults to try and determine their migration routes. Leatherbacks are extremely powerful swimmers, with all the work done by the front flippers while the rear flippers aid in steering.
However, “over the last few years, scientists working with a National Geographic Crittercam team in Costa Rica have attached underwater Crittercams to leatherbacks, documenting the world's largest living reptile in its seldom seen underwater environment. The resulting footage has shed light on rarely seen mating behavior, captured on film perhaps for the first time” (Pickrell). The Crittercam documents surprising pieces of information that is very unfamiliar. The captured footage reveals aggressive attempts by males to mate with the females returning to the open ocean. This indirectly states that the mating activity actually occurs near the nesting beaches after they lay their eggs and not before their migration to the nesting location. What was extremely surprising to the Crittercam team was the force involved in mating. The footage revealed that males repeatedly strike and bite the females and prevent them from returning to the surface to breathe.
Unfortunately, over the past 11 years, there has been a rapid decline of leatherbacks from a population of about 1,350 female nesters per season to about 130-140 who have nested in the past three years. This world-wide decline is the result of over 15 years of human activity, including poaching of eggs laid by returning females, the loss of many nesting beaches to development for hotels, resorts, and private homes, and the accidental capture by shrimp and gillnet fishing vessels. Humans’ activities have directly driven this species close to extinction. As a result, these giant, marine reptiles have disappeared completely from many historically important nesting areas. “From the 1970s to the early 1990s, organized nest poaching was the greatest threat facing Costa Rican nesting turtles- their eggs are still a delicacy in some parts” (Pickrell). Reina, a conservation lecturer at Monash University in Melbourne, Australia, states that for maybe 15 to 20 years, nearly all the eggs were stolen. These eggs were then sold either for cooking purposes, or to be drunk with a shot of alcohol. Though poaching is now no longer a severe threat in Costa Rica, sea turtles are being massively affected by fishing practices, which need to be changed immediately so that turtles can’t be caught by nets or longlines, or don't drown if they are caught. A study found in the Marine Ecology Progress Series estimated that up to one in three turtles are unintentionally killed at the hands of fishermen each year. “Another study suggested that longline and gill net fisheries killed as many as 1,500 leatherbacks each year in the Pacific during the 1990s” (Pickrell). “The reluctance of many countries to sign the International Sea Turtle Conservation Convention that is designed to protect these animals has led to the current sorry state of affairs. I believe that these rulings and the lack of concern will lead to the extinction of leatherbacks, at least in the Eastern Pacific, unless something is done to change the patterns we now see” (Paladino).
Leatherback turtles have been nesting on the Pacific coast of Costa Rica for thousands or millions of years. During the 1980s it was realized that the beaches of Playa Grande, Playa Ventanas and Playa Langosta hosted the largest remaining Pacific leatherback populations in Costa Rica. Biologists quickly discovered that these populations were declining.
Las Baulas National Park is located on the Pacific coast of Costa Rica in the Province of Guanacaste, near the village of Tamarindo. This park supports the largest nesting “colony” of leatherback turtles in the Pacific Ocean with a population size of about 800 female turtles nesting per year in non-El Ni–o years. The presence of an El Ni–o year in the Pacific is correlated with very low numbers of nesting leatherbacks at Las Baulas.
The protection at Las Baulas began in 1988 when Maria Teresa Koberg, known as the turtle mother of Costa Rica, started to bring Boy Scouts, students, and friends to the beach to help stop poaching. She converted local poachers to protectors and guides, and campaigned forcefully to get the Park established by decree in 1990 and then law in 1995.
This park is one of the world's few remaining sites of significant leatherback turtle nesting activity. It is made up of three nesting beaches, including Playa Grande which is 3.5 km long, Playa Langosta which is 1.3 km long, and Playa Ventanas which is 1.0 km long. It also protects two mangrove estuaries, Estero de Tamarindo, the largest mangrove estuary in Central America, and the smaller Estero de San Francisco, as well as the ocean out to 12 miles offshore. The National Park guards are thus responsible for protecting the turtles and their nests.
Dr. Frank V. Paladino, from the Department of Biology at Indiana-Purdue University, and his colleagues have studied the Las Baulas (Spanish for Leatherback turtle) National Park through their EARTHWATCH Inc. project. “Faculty, students, and volunteers conduct scientific investigations of the turtles and their eggs and help in local conservation efforts and protection” (www.leatherback.org). They have observed more than a 40% mortality rate in the returning adult female population over the last eight years. They have conducted aerial surveys and checked beaches all along the Costa Rican coastline to make sure that these females who have not returned are not just nesting elsewhere. They found that there are very few beaches left where the leatherbacks still nest.
The Las Baulas Project is dedicated to protecting and understanding the population of turtles nesting in the National Park so that the species may be saved. The project takes place each year during the nesting season from late September to March. The Principal Investigators are Dr. Frank V. Paladino, Dr. James R. Spotila from Drexel University, Pennsylvania, Dr. Richard Reina from Monash University, Australia, and Dr. Paul Sotherland from Kalamazoo College in Michigan. Students, local community members and volunteers from the non-profit organization, Earthwatch, come to work with the National Environment Ministry, Ministerio del Ambiente y Energia (MINAE), to protect nesting turtles and collect vital information on nesting biology. This information is shared with MINAE and the general scientific community in order to develop the most effective strategies for management and conservation of the endangered population.
The Las Baulas project aims to identify the size and status of the nesting leatherback turtle population and to protect nesting female turtles and their nests from poachers and predators. It also plans to work with the Costa Rican authorities to develop effective management and conservation strategies and to improve the understanding of leatherback biology through quality scientific research. However, in order to achieve these ideals, the nesting beaches need to be patrolled each night and all nesting turtles identified and the assisting park guards need to be in control of tourists and other beach visitors. The local government, the National Park authorities, and the members of the local communities all need to meet in order to distribute information and provide advice in conservation issues. A variety of research projects need to be accepted to investigate reproductive biology, population genetics, physiology and other important areas of biology.
The conservation of these turtles faces many challenges at Las Baulas, ranging from overdevelopment, through excessive tourism activities, to the stealing of eggs. The National Park has been constantly understaffed, resulting in unprotected beaches. Despite an active education campaign, local residents still steal/poach eggs from the beach. Tourists visit to the beaches with the expectation of seeing the leatherbacks and often overcrowd a nesting turtle, despite cautions from their local tour guides. Development continues behind the beach and the increasing lights from new houses and the village of Tamarindo, disorient hatchlings and adults. Although Las Baulas is remote from the more populated centers of Costa Rica, it suffers from the same pressures found on sea turtle beaches in Florida, Greece, and other location around the world. EARTHWATCH teams, concerned local residents, guides, local business leaders and scientists continue to work to help improve the protection provided by the Park. Larry Crowder, a sea turtle expert at Duke University believes that "The level of protection in Costa Rica is as good as it gets … and [is] the ideal situation we'd like to see at all nesting beaches” (Pickrell).
Paladino, Frank V. "Are Leatherbacks Doomed to Extinction?" Costa Rican Sea Turtles PI. http://users.ipfw.edu/paladino/default.htm
Pickrell, John. "Leatherback Sea Turtle Mating Filmed for First Time". National Geographic. February 12, 2004. http://news.nationalgeographic.com/news/2004/02/0212_040212_leatherbackcam.html
The Leatherback Trust. 2003. www.leathrback.org
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