Sea turtles inhabit warm waters of our planet’s oceans, bays and estuaries.  They are similar to their terrestrial (land) cousins, the tortoises, and to freshwater turtles, except that their legs have been modified into flippers to aid them in swimming.  Their shape has taken on a flattened, more streamlined appearance – tapering off in the rear to allow for less water resistance during swimming.  All sea turtles except the leatherback turtle have a hard carapace (top shell) and another hard shell on the belly called the plastron.  The carapace, as with all other turtles, incorporates their backbone, sternum and ribs.  This is unlike most other animals whose backbone and ribs are free of a shell or skin.

Sea turtles are closely related to ancient species dating back 130 million years to the Cretaceous Period.  Some may be more closely related to dinosaurs than our present day reptiles.Like all other reptiles, sea turtles’ body temperature depends upon their surroundings which explains their migration southward as northern waters  cool off in the fall.  The leatherback turtle, though, has recently been found to be able to create some body heat, thus making them able to withstand the chilly waters off Canada and Iceland, where they roam in the summer. Sea turtles are air breathers, but are capable of holding their breath for quite some time.  It is thought that they are also able to absorb oxygen from their skin, mouth and their cloaca.

There are four species of sea turtles that nest along the Pacific coast of Costa Rica.  They are the green sea turtle (Chelonia mydas), the olive ridley sea turtle (Lepidochleys olivacea), the hawksbill sea turtle (Eretmochelys imbricata), and the leatherback sea turtle (Dermochelys coriacea).  All four species are listed on The World Conservation Union (IUCN) Red List as either Endangered (EN) or Critically Endangered (CR).Until the 18th and 19th centuries, marine turtles were abundant in tropical and subtropical oceans worldwide.  Today, few populations remain within their historical distributional scope and many populations that once numbered hundreds of thousands of individuals have been reduced to just a couple of thousand, with the majority of this reduction occurring over the course of the last century.

The colossal decline in sea turtle populations is the result of many factors which include; the consumption of turtle meat and eggs as well as the collection of turtle carapaces and fat for commercial and home use, the deterioration of nesting beaches, foraging areas and mating sites, loss of nesting habitat due to the construction of beachfront homes and hotels and other activities related to tourism, the compaction of sand due to cars and foot traffic and the extraction of sand from nesting beaches for use in construction and other activities.

However, without a doubt one the most damaging activities today, not only to sea turtles, but to marine life in general, is the commercial fishing industry.  Longliners and shrimp trawlers kill hundreds of thousands of sea turtles as well as huge numbers of birds, fish, cetaceans, and pinnipeds, each year.

Protection, conservation and restoration of sea turtle populations and their critical habitats has lead to a huge number of protection programs worldwide.  In many cases the most effective initial steps that can be taken by programs is entering communities located near nesting beaches and informing community members on the critical state of sea turtle populations and discouraging them from consuming marine turtle products (eggs, meat, carapace, etc.).   However, the custom of using marine turtle products is rooted in years of tradition by many cultures and expecting these traditions to change rapidly is unrealistic.  It is important to involve the community members in the projects, bring them alternatives to their destructive practices, and give them incentives against the exploitation of sea turtle products.

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OLIVE RIDLEY SEA TURTLE

(Lepidochelys olivacea)

The olive ridley is the smallest of the sea turtles.  Adults measure 55 to 70 cm in carapace length and weigh between 35 and 45 kg.

They reach sexual maturity when 10 to 15 years old and probably live to be 50 or 60.  Nevertheless they are sexually active for no more than 21 years.

The females usually nest every two years.  However, they sometimes nest every three years and sometimes every year.  A single turtle can nest three times in a season with intervals of 17 to 28 days.  The nesting season is from June to December.  Olive ridleys also nest on beaches in Mexico, Nicaragua, Honduras, Panama, Colombia and are found in the Pacific and Indian oceans.

The average depth of their nests is approximately 45 cm and the average number of eggs per nest is approximately 105.  Eggs incubate in the nests from 40 to 65 days.  Hatchlings measure from 2.5 to 4 cm in carapace length.

In Costa Rica the name for olive ridley is tortuga lora which translates directly as parrot turtle.  They are called this because their beaks resemble a parrot’s beak.  They are called olive ridleys in English because the color of their shells is olive green.  These turtles are omnivores and eat crustaceans, mollusks, fish and some marine vegetation.

Olive ridleys especially like to float at or near the surface of the water to warm themselves.  In fact the shape of their carapace facilitates absorption of the sun rays.  They can dive for up to 30 minutes to depths of 200 m.

Only two species of sea turtles, the kemp¢s ridley and the olive ridley, perform the phenomenon known as “arribada”.  This occurs when thousands of turtles arrive to nest at one beach at the same time during three or four days, especially when the moon is waning.  In Costa Rica there are two beaches, Ostional and Nancite, where olive ridley arribadas occur.  Both are in the Guanacaste province and the largest arribadas usually occur between the months of June and December.

However, olive ridleys also do solitary nesting in many beaches on the Pacific coast including: Punta Banco, San Miguel, Caña Blanca, Playa Caletas, Camaronal, Carate, Esterillos, Playa Hermosa, Nosara and Mata Palo.  It has been confirmed that some of the olive ridleys that nest in Costa Rica migrate to Mexico, Nicaragua and Peru.

Olive ridleys, like other sea turtles, are in danger of extinction.  One of the reasons is the consumption of turtle eggs by humans and animals.  Another reason is accidental capture by commercial fishing fleets.  These turtles feed on shrimp and are caught in shrimp nets and as they are only able to hold their breath for 15-30 minutes they drown.  They are also accidentally captured on hooks used by Commercial longliners.

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GREEN SEA TURTLE (Chelonia mydas)

The green turtle has a carapace of 80 to 100 cm in length and can weigh up to 100 kg.

Green turtles reach sexual maturity when they are 16-25 years old.

The females nest every two or three years.  A single female can nest up to three times per season with an interval of 12 to 14 days.  The nesting season for black turtles on the Pacific coast of Central America is from September to March.

Nests are approximately 50 cm deep.  The number of eggs per nest ranges from 65 to 87.  Eggs incubate in the nests on average 42 to 62 days.  These turtles nest sporadically on the Pacific coast of Costa Rica on beaches such as Playa Caletas, Nombre de Jesus, Naranjo, Cabuyal, Carate and Rio Oro, among others.

Green turtles are for the most part herbivores and feed on algae.  They are found in Mexico, El Salvador, Nicaragua, Costa Rica and Colombia.

Green turtles are endangered principally due to consumption of their meat and eggs.  However, they are also captured accidentally by commercial fishing fleets.  During the last three years, dozens of dead green turtles have washed up Pacific beaches in Costa Rica.  They have had injuries on their abdomens, or evidence of capture in nets and on hooks.

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HAWKSBILL SEA TURTLE

(Eretmochelys imbricata)

The hawksbill turtle has a carapace length of 70 to 95 cm and weighs between 42 and 77 kg.

Females nest every two or three years and in a single season can nest up to five times in intervals of 14 to 16 days.  The nesting season on the Pacific coast is May to January.

The average number of eggs in each nest is 160.  Eggs incubate for 47 to 75 days.  The average nest depth is 40 cm.  Hatchlings have 3.8 to 4.5 cm carapace length.  Hawksbills feed mostly on marine sponges but also consume other invertebrates and algae.

Hawksbills are near extinction because their beautiful shells are used for different products and to obtain the shell the turtle must be killed.  Their eggs are also consumed by humans.

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LEATHERBACK SEA TURTLE

(Dermochelys coriacea)

The leatherback sea turtle is the largest sea turtle and the largest reptile on the planet.  These turtles are found in the Atlantic and the Pacific.  In general, the Pacific leatherbacks are slightly smaller.  They weigh between 300–400 kg and have an average carapace length between 1.4 and 1.8 m.

Leatherbacks reach sexual maturity after 10 years.  Females nest every two or three years and are able to nest up to six times during a nesting season with intervals of 9 days.  The nesting season on Pacific beaches lasts from September to March.

The average number of eggs per leatherback nest is between 80 and 90 with approximately 30 infertile eggs.  Average depth of nests is 75 cm.  Eggs incubate from 50 to 70 days.  Hatchlings have an average carapace length from 5-6.5 cm.

Leatherbacks migrate great distances.  From their nesting beaches in the tropics they migrate to temperate zones and even sub-polar regions where they have feeding grounds.  Satellite tags on these turtles have shown that after nesting in Costa Rica, they migrate south and west to Coco Island and the Galapagos and continue on along the coast of South America all the way to the cold waters of Chile. Of all the sea turtles, leatherbacks are able to dive to the deepest depths – down to 800 m.  It is also the fastest swimmer and is able to travel 70 km per day.

Unlike other sea turtles, the leatherback does not have a carapace of bone and scales.  Rather their carapace is cartilage, rich in oil, with bony plates and covered with skin that is very dark in color with white spots.  Their skin is smooth and lacks scales.  Leatherbacks are the only turtles capable of regulating their body temperature and maintain it above that of surrounding waters.  This allows them to survive in cold waters where they have feeding grounds.  Their diet is very specialized as they feed strictly on jelly fish.

Leatherbacks’ most important nesting beaches are found in Mexico, Nicaragua and Costa Rica. Unfortunately LEATHERBACKS ARE DISAPPEARING at alarming rates.  Playa Grande, in the Leatherback National Park in Costa Rica, is the most important leatherback nesting beach on the Pacific, yet numbers of nesting turtles have plummeted over the past decade. Optimistic estimates put the number of remaining leatherbacks world wide at 30 000.  Eastern Pacific Leatherbacks are showing the greatest decline and it is estimated that only 2,500 nesting females are left in existence.  This species could be extinct within 15 years if something is not done to stop the decline.