Leatherback sea turtles are modern-day dinosaurs.
The leatherback life cycle begins with a female turtle laying eggs on a nesting beach. Females stay close to shore in “internesting habitats” for 3-4 months and make repeated visits at 10-day intervals to lay eggs. Adult females depart for pelagic habitats to forage and remain there for an average “remigration interval” of 2-5 years until they return to nest once again.
About 55-60 days after the female lays eggs, hatchling turtles emerge from their nests, head to the sea and follow ocean currents to pelagic nursery habitats, where they search for food and seek refuge from predators. Scientists refer to this time period as “the lost years”, since finding hatchlings and juveniles to study in the open ocean is difficult.
After 15-25 years leatherbacks reach maturity. Mature female turtles return to their natal beaches for nesting, but adult male turtles live entirely at sea.
Female leatherbacks usually lay their eggs at night. Nesting turtles may decide not to nest if there are too many lights onshore. Those that come ashore seek nesting sites free of debris (tree limbs). If the turtle does not find a suitable site for her nest, she may return to the ocean without laying.
Leatherbacks carve out an egg chamber about 75 centimeters (inches) deep in the sand, where they deposit 65-115 eggs. (East Pacific leatherbacks are known to lay fewer eggs than their counterparts in the Atlantic.) Only 85 percent of these eggs are viable, as some have no yolk to develop into an embryo.
A leatherback can lay 7 to 11 individual nests per season, laying a new nest every 10 days. Between nesting seasons, females will spend 3-4 years feeding to build up enough energy to nest again. Older females typically lay more nests with more eggs than turtles that have recently reached maturity.
The sex of turtle eggs is determined by the temperature of the nest. During the middle third of incubation (days 20-40) the temperature within the nest determines the ratio of males to females; warmer temperatures mean more females while cooler temperatures yield more males.
After an incubation period of 60 days the eggs will begin to hatch. The hatchling turtles must emerge from the nest and make their way to the ocean. Ten percent of hatchlings will be eaten by seabirds, crabs, reptiles and mammals on the beach. Only 25 percent of hatchlings will make it through their first few days in the ocean. Just 6 percent of hatchlings will survive their first year.
Images by Jason Bradley and Brian Skerry.
Although leatherback turtles nest in the tropics, they principally feed (also called foraging) in cold waters far from the equator, such as those of Chile, California, Canada, northern Europe, southern Africa and New Zealand. These areas are most abundant in jellyfish, which are a primary food source for leatherback turtles.
Scientists divide leatherbacks into seven subpopulations: East Pacific Ocean, West Pacific Ocean, Northwest Atlantic Ocean, Southeast Atlantic Ocean, Southwest Atlantic Ocean, Northeast Indian Ocean, and Southwest Indian Ocean.
We do not know how leatherback turtles navigate the great distances between their feeding grounds and their nesting beaches. However, we do know that turtles follow common paths between nesting and feeding habitats. Scientists refer to these paths as migration corridors.