Unique reproductive activities of rare sea turtles in Con Dao National Park

Every year, during the breeding season, Green turtles (Chelonia mydas), also known as Green Turtles, from distant oceans, return to Con Dao National Park. Here, they mate and build nests to lay eggs.

Độc đáo hoạt động sinh sản của rùa biển quý hiếm tại Vườn quốc gia Côn Đảo

Con Dao National Park (Ba Ria - Vung Tau) is the first place in Vietnam to successfully implement a sea turtle conservation program. (Source: Lao Dong Newspaper)

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According to records, in the sea of Con Dao, there are 4 species of sea turtles: Green turtle (Chelonia mydas), Hawksbill turtle (Eretmochelys imbricata), Green turtle (Lepidochelys olivacea), and Loggerhead turtle (Caretta caretta). Of which, the population of Green turtles that come here to lay eggs every year is the largest in Vietnam.

Based on data tracking mother turtles migrating to lay eggs on beaches, scientists estimate the average lifespan of sea turtles to be around 50 years. Green turtles are one of the species with the longest lifespan, up to 70-80 years.

Research by the Department of Conservation and International Cooperation - Con Dao National Park shows that the Green turtle has an average diameter of 93 cm long, 84 cm wide, and weighs 90 kg. This species nests all year round, but peaks from May to October.

Close-up of Green turtles mating near shore. (Photo: Phung Hai/ Con Dao National Park )

During the breeding season, Green turtles migrate from their feeding grounds to their nesting grounds. The mating period lasts 1-2 months, on the migration route and before the nesting grounds. During this period, sea turtles have a short mating period of 2-3 minutes, and a long period of 72 hours of continuous attachment. On average, a female turtle spends 25 hours/season mating and there is no bond between pairs.

A female turtle can have several mates and vice versa. After 2-4 weeks of mating, the male turtle migrates to the feeding area, the female turtle goes to the nesting beach to lay eggs for the first time.

Green turtles make nests to lay eggs. (Source: Lao Dong Newspaper)

As an employee who has been involved in sea turtle conservation for many years at Con Dao National Park, Mr. Nguyen Van Vung, an expert from the Department of Conservation and International Cooperation, said that it takes about 2-3 hours for green turtles to build a nest and lay eggs. Green turtles usually come to the nesting ground at high tide, they use their two front limbs to dig the upper part of the nest, and their two hind limbs to dig the lower part of the nest. The nest is about 60-70cm deep. Once the nest is dug, the turtles start laying 1-4 eggs at a time, with the time between each egg falling being 30 seconds to 1 minute.

The average number of eggs per nest is 85, the eggs have an average diameter of 5 cm and an average weight of 56g. After a period of 11-13 days of resting from egg production, the mother turtle continues to lay eggs for the second time. Each mother turtle lays an average of 3 nests per year, the reproductive cycle between two seasons is from 1-5 years. Notably, in Con Dao, there is a mother turtle that lays 11 nests per year and reaches a record number of eggs of 993 eggs.

The average number of eggs per nest is 85. (Source: Con Dao Explore)

Mr. Vung added that from the time the eggs are laid, the next 6 hours are the time when the embryo stops developing, the eggs can withstand light collisions and disturbances. During this time, unsafe nests on the beach are moved to artificial incubation ponds designed to resemble mother turtle nests on natural beaches.

In a turtle egg nest, if the temperature is 30 degrees Celsius, the ratio of females is greater than males; if the egg nest temperature is 26-30 degrees Celsius, the ratio of males and females is 50/50. The average hatching time for baby turtles is 55 days, the hatching rate is 83%.

After 2–3 days of hatching, the baby turtles will emerge from the ground mainly at night, when the weather is cool and the tide is high, and crawl down the beach, heading straight for the ocean by sensing the light of the stars, the tides and the Earth's magnetic field. The baby turtles swim continuously for 1–2 days in a state called "swimming in the dark" to get as far away from the shore as possible.

After hatching, baby turtles crawl out of the nest and head towards the ocean. (Source: Con Dao Explore)

The baby turtles then drift as plankton in the ocean for several years until they migrate from deep ocean waters into shallow waters with seagrass beds, coral reefs, and mangroves to feed. After 25–30 years, they reach adulthood and make their first migration to the mating and nesting areas where they were born.

After the mating season, the males swim back to their feeding grounds, and the females go to the egg-laying grounds. After the egg-laying season, they swim back to their original feeding grounds. And so the sea turtle life cycle continues over time.

Safe habitat for sea turtles

Con Dao National Park has 18 sandy beaches with a length of about 3.5km and an area of 24ha, which are recorded as turtle nesting grounds. Of these, Bai Cat Lon-Hon Bay Canh, Bai Duong-Hon Bay Canh, Hon Cau, Hon Tai and Hon Tre Lon are 5 areas where turtles lay eggs regularly, with more than 150 mother turtles coming to lay eggs every year.

Statistics from Con Dao National Park show that from 1993 to 2023, 11,643 mother turtles came to the beach to nest and lay eggs, of which 31,400 nests with a total of 2,898,640 eggs were successfully rescued and relocated, hatching and releasing 2,238,597 baby turtles back to the sea; the rate of turtles hatching and being released back to the sea reached over 80%.

Campaign to clean up and remove obstacles on the sand to facilitate mother turtles to lay eggs. (Source: Con Dao National Park)

In addition, Con Dao National Park has tagged more than 5,750 mother turtles to monitor the biological and morphological characteristics of the nesting sites. The results show that on average, each season, mother turtles lay 3 nests. After 3 years, mother turtles return to Con Dao to lay eggs once. Each nest contains 90 eggs and after 55 days of natural incubation, the baby turtles will hatch.

In the first two months of 2024, sea turtles successfully laid 50 nests on the beach, hatching 134 nests (cumulative nests in the last months of 2023). Forest rangers, volunteers, and tourists released more than 8,000 baby turtles into the sea under control.

Tourists watch baby turtles leave their nests and head for the sea.

Sea turtles are on the brink of extinction and are listed in the Red Book of Vietnam and the world. Vietnamese law strictly prohibits the hunting, capture, trading, transporting, and using of sea turtles and their products.

Every night, the sea turtle nesting grounds are patrolled and protected by rangers. These grounds are regularly cleaned and leveled to create favorable conditions for mother turtles to lay eggs. After the turtles lay eggs, the nests are moved and relocated to incubation ponds to ensure a high hatching rate and avoid losses due to disadvantages from nature and humans. Most of the life cycle of sea turtles, from birth in eggs to adulthood, face many threats from nature and humans.

Con Dao National Park is the first place in Vietnam to successfully implement a sea turtle conservation program. Each year, about 450 mother turtles come to the nesting grounds and more than 150,000 baby turtles are released into the sea.

On December 1, 2022, Con Dao National Park was honored to receive a Certificate of Merit from the Prime Minister for "Achievement in Sea Turtle Conservation".

Previously, on January 31, 2009, the Garden was recognized by the Vietnam Record Book Center as the "Place that incubates and releases the most baby turtles into the sea in Vietnam".

(according to VNA)

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