The Secret Lives of Nesting Sea Turtles—And Why Few Babies Survive

There are seven species of sea turtle alive today, and they are found in oceans all over the world except the Arctic. Many of them travel thousands of miles between the areas where they forage for food and the places where, like the female in this fascinating Instagram post, they lay eggs in nests on beaches. Take a look for yourself and then read our guide on sea turtle reproduction and egg clutches.

Sea Turtle Biology

Sea turtles have a few common characteristics. They have scaly skin, which helps them conserve moisture in salty environments, and they are poikilothermic, meaning their body temperature varies according to their surroundings. They breathe air (so they cannot breathe underwater) and are oviparous, meaning they lay eggs. In most sea turtle species, it is only the adult females that ever leave the water, and they do this to lay their eggs on land. All sea turtles share similar life cycles and reproductive behaviors.

Nesting Sea Turtles

Mating takes place at sea, and females can mate with more than one male. This means that a single nest can have eggs containing embryos that have different fathers. The females may travel thousands of miles to nest on the same beach where they were hatched. This behavior is called natal homing.

After locating the beach, most species emerge from the water at night to avoid predators and extreme heat. Moving along the sand is difficult for sea turtles; they must use significant effort to haul themselves forward with their flippers. If she is disturbed, she will abandon the nesting attempt and return to the sea. This is known as a ‘false crawl’.  When she reaches a spot above the high tide line, she clears away debris and begins to dig with her front flippers.

Sea Turtle Clutches

The number of eggs in a nest is called a clutch, and a sea turtle clutch is around 110. Flatback sea turtles lay around 50, but hawksbill sea turtles can lay over 200. In general, the smaller species lay the most eggs. As she lays the eggs, the sea turtle enters a trance-like state. When she has finished, she covers the hole with sand using her hind flippers and pats it down. Then, she hides its location by flicking sand and debris over it. Once the job is complete, she makes her way back down the beach to the sea, where she rests for 10 to 15 days before repeating the process. Each female will create between two and eight nests in one season.

At the end of the nesting season, her energy reserves are depleted, and she returns to her feeding area to recover. It is typically 2 to 4 years before she nests again, though this interval can vary by species and individual.

Meanwhile in the Nest…

Sea turtle eggs have soft shells and remain moist in the sand, allowing oxygen to diffuse into the developing embryos. The eggs will incubate for around 60 days, but the hotter the temperature of the sand, the faster they will develop. Additionally, warmer sand temperatures cause the eggs to develop into females, while cooler sand results in males.. Some nests produce only one gender, but more commonly, the warmer parts of the nest produce females, while the cooler (often deeper) parts produce males.

The Dangers of Hatching

Baby turtles have a temporary tooth-like structure (a caruncle) that they use to break out of their shell. They all hatch together in a short space of time and work as a team to dig their way out of the nest. Even so, it still takes them up to five days to do this.

They usually emerge at nightfall because it is safer and cooler. Guided by the moon reflecting light on the horizon and the downward slope of the beach, they head down to the sea. During this journey, they are in danger of being picked off by sea birds and crabs as well as land-based predators such as foxes and raccoons. By making the perilous journey as a group, they increase their chances of survival.

Once in the water, they swim frantically to reach deeper, safer areas. What happens next is not entirely known, but they likely hide in algae mats (sargassum floats), where they are safer as they feed and grow.

Despite all of this considerable effort, the survival rates for baby turtles are extremely low. It is estimated that between one 1,000 and 1 in 10,000 will survive to adulthood. Most sea turtles reach sexual maturity between 20 and 35 years of age, though in some cases it may take up to 50 years. Then, they will make the long journey back to their nesting grounds to mate, and the whole cycle will start again.