Sea Turtles' Reproduction: Mating And Nesting Habits Explained

Sea turtles are fascinating creatures with a complex reproductive process. They are generally solitary, only coming together during mating season, which can be a dangerous activity. The female sea turtle has to support the weight of the male while they are both underwater, and she must regularly surface for air. After mating, the female sea turtle will migrate to a beach, usually the one where she was born, to lay her eggs. She uses her flippers to dig a nest and lay anywhere from 50 to 200 eggs, depending on the species. The temperature of the sand determines the gender of the hatchlings, with cooler sand producing more males, and warmer sand resulting in more females.

Sea turtle mating

Sea turtles typically live solitary lives, only coming together during mating season. The male and female will copulate in the water, just offshore, with the male holding onto the female's shell with his claws. The female has to support the weight of both of them while also regularly surfacing for air. This can be a dangerous activity for both turtles.

During courtship, the male will approach the female and gently bite her neck and flippers. If she does not try to escape, the male will climb onto her back and attach himself to her shell. The male's long tail reaches under the posterior end of the female's shell to inseminate her cloaca. Copulation can take place on the surface or underwater and can last several hours. After mating, the male will try to hang onto the female to prevent other males from mating with her. Several males may compete for a single female, aggressively biting her suitor to make him let go.

After mating, the female will return to the beach where she hatched years before to lay her eggs. She will dig a nest in the sand above the high water mark, using her back flippers. The depth of the cavity is determined by the length of her stretched hind flipper and can be up to one metre deep. She will lay up to 100 eggs, which are fertilised by a variety of males. The eggs are surrounded by a thick, clear mucus and do not break when they fall into the cavity. The female then covers the nest with sand, which helps protect the eggs from predators, keeps them moist, and maintains the correct temperature.

The temperature of the sand determines the gender of the hatchlings, with cooler sand producing more males and warmer sand producing more females. After around 60 days, the baby turtles will hatch and rush to the sea, increasing their chances of surviving waiting predators.

Sea turtle nesting

Choosing a Nesting Site:

Pregnant female sea turtles return to the beaches where they hatched years before. They swim through the surf and crawl up the beach, searching for a suitable nesting spot above the high water mark. They prefer sandy beaches, and the temperature of the sand will determine the gender of their offspring, with cooler sand producing more males and warmer sand resulting in more females.

Constructing the Nest:

Using their back or hind flippers, female sea turtles dig a nest in the sand, creating a "body pit" and then an egg cavity. This process can take anywhere from one to three hours. The depth of the cavity depends on the length of the stretched hind flipper and can be up to one metre deep. The shape of the cavity is roughly like a teardrop and is usually tilted slightly.

Laying and Burying the Eggs:

Once the egg chamber is ready, the female begins to lay her eggs. Sea turtles can lay anywhere from 50 to 200 eggs, depending on the species, with an average clutch size ranging from 80 to 120 eggs. The eggs are soft-shelled and coated in a thick, clear mucus, which prevents them from breaking when they fall into the egg cavity. The female covers the nest with sand using her hind flippers, helping to protect the eggs from predators, maintain moisture, and regulate temperature.

Returning to the Ocean:

After laying her eggs, the exhausted mother turtle slowly drags herself back to the ocean, leaving the nest untouched. She will not return to tend to the nest, and once she has left, the eggs are on their own. The female may nest multiple times during the nesting season, taking breaks in between to rest and regain her energy.

Incubation and Hatching:

The sea turtle eggs incubate in the warm sand for about 60 days. The temperature of the sand governs the speed of embryonic development, with hotter sand resulting in faster development and a higher ratio of female hatchlings. When the tiny turtles are ready to hatch, they do so simultaneously, creating a "turtle boil" as they erupt from the nest and rush towards the ocean together to avoid waiting predators.

Sea turtle egg-laying

Sea turtles are migratory, traversing hundreds of kilometres from their main feeding areas to nest on the beaches where they hatched. This annual migration also occurs in some river-dwelling turtles, which move tens of kilometres along rivers to find large sandbars to nest on.

Female sea turtles emerge from the sea at night and crawl up the beach, searching for a suitable nesting site somewhere dark and quiet. Once she has found a spot, the female sea turtle uses her flippers to dig a "body pit" and then an egg cavity, which can be up to 1 metre (3.3 feet) deep. The depth of the cavity is determined by the length of the stretched-out hind flipper. The whole process of digging the nest and laying her eggs usually takes from one to three hours.

A female deposits between 50 and 200 eggs (depending on the species) into the egg cavity. The eggs are soft-shelled, with a papery to leathery texture, and are surrounded by a thick, clear mucus. They are spherical and about the size and shape of ping-pong balls. The female then covers the nest with sand using her hind flippers. Burying the eggs helps protect them from predators, keeps the porous shells moist, and helps the eggs maintain the proper temperature.

The female sea turtle may spend two or more hours out of the water during the entire nesting process. After covering the nest, she slowly drags herself back to the ocean.

Sea turtle incubation and hatching

Sea turtle incubation begins when the female turtle crawls up the beach and uses her back flippers to dig a nest in the sand. The depth of the nest depends on the length of the turtle's stretched hind flipper and can be up to 1 metre (3.3 feet) deep. The female then deposits between 50 and 200 spherical, soft-shelled eggs into the nest, which are surrounded by a thick, clear mucus. The number of eggs laid depends on the species of sea turtle. For example, green sea turtles lay an average of 110 eggs per clutch, while leatherback nests typically contain 50 to 100 eggs.

The female sea turtle then covers the nest with sand using her hind flippers. Burying the eggs helps to protect them from predators, keeps the porous shells moist, and maintains the proper incubation temperature. The incubation period for sea turtle eggs typically lasts between 45 and 70 days, although some sources state that it can be as short as 60 days. The temperature of the sand or nest during incubation determines the gender of the baby sea turtles, with cooler temperatures resulting in more male hatchlings and warmer temperatures producing more females. This phenomenon is known as Temperature-Dependent Sex Determination (TSD).

After incubating for about two months, the sea turtle eggs hatch, and the baby turtles use a temporary egg tooth called a carbuncle to help break open their shells. The hatchlings then climb up through the sand and emerge from the nest at night, usually waiting until darkness to reduce exposure to predators. The tiny turtles, measuring between 1.5 to 3 inches in length, rush to the sea all together in a "swim frenzy" to overwhelm waiting predators. They find their way to the ocean by discriminating light intensities and heading towards the greater light intensity of the open horizon. Once they reach the surf, the hatchlings dive into the waves and ride the undertow out to sea, where they will spend their early years hiding and growing.

Sea turtle reproduction challenges

Sea turtles face a multitude of challenges when it comes to reproduction. Firstly, they have a long wait before they can reproduce, with sexual maturity taking anywhere from 7 to 40 years to reach, depending on the species. For example, leatherbacks reach maturity at around 7-13 years, while green sea turtles take 26-40 years.

Once sexually mature, female sea turtles return to the beaches where they hatched to lay their eggs. They come ashore at night, alone, and during high tide. The nesting process is dangerous and time-consuming, with females spending up to 3 hours digging a nest, laying their eggs, and covering them with sand. They lay up to 200 eggs, which are soft-shelled and vulnerable to breakage if not carefully handled. The temperature of the sand determines the gender of the hatchlings, with cooler sand producing more males and warmer sand producing more females.

After incubating for about 60 days, the hatchlings emerge and rush to the sea, trying to avoid predators. Unfortunately, many hatchlings fall prey to seabirds, foxes, raccoons, and wild dogs. Those that survive spend their early years hiding and growing in offshore areas.

Human activities pose significant threats to sea turtle reproduction. They suffer from poaching and over-exploitation, with their meat, eggs, skin, and shells being sought-after commodities. Climate change also affects nesting sites by altering sand temperatures and disrupting the normal gender ratios of hatchlings. Additionally, uncontrolled coastal development, vehicle traffic on beaches, and other human activities have directly destroyed or disturbed nesting beaches.

Frequently asked questions