There are seven species of sea turtles swimming the world's oceans. Six of the species can be found in U.S. waters: greens, hawksbills, loggerheads, leatherbacks, olive ridleys and Kemp's ridleys. A seventh species, the flatback, only inhabits the waters around Australia.
Female sea turtles, like all other reptiles, lay eggs. Most sea turtle species crawl onshore to nest during the night, although Kemp's ridleys and olive ridleys are also known to nest during the day.
In laying a nest, also called a “clutch”, a female excavates a sandy pit using her hind flippers, and then deposits 30-200 eggs, depending on the species. Once a female lays and burys her eggs, she immediately returns to the water, leaving her eggs unattended.
The sex of a baby turtle is determined by sand temperature, with more females hatching at higher temperatures. Along the Atlantic coast of the U.S., temperatures are cooler farther north so the farther north a turtle nests, the higher the likelihood the hatchlings will be male.
After an incubation period of about 6-10 weeks, depending on the species, hatchlings “pip” or break through their eggshell and begin the tiring crawl out of their sand covered nesting chamber. Using the natural light of the moon and other cues, hatchlings anxiously make their way for the sea and start swimming in the direction of the waves.
While in their nests and on their journey to the water, there are many threats, including being crushed by humans and vehicles, predation by birds and other animals and disorientation by artificial lighting -- but the threats do not stop there. Once in the water, they face additional predators plus challenges like pollutants, dredging, marine debris, vessel collisions and fishery interactions.
When hatchlings enter the water, they begin a “swim frenzy” away from the coastline. Because little is known about what occurs during this time, many researchers refer to the first few years of a hatchling's ocean life as “the lost years.”
Even as sea turtles reach maturity, they are still at risk from predators, including sharks, killer whales and in some places, crocodiles. Some of the larger and slower growing turtles, like loggerheads, do not reach sexual maturity until they are about 32 years old.
Other smaller sea turtle species, such as the Kemp's ridley, can reach maturity as early as 7 years of age. Once female turtles reach maturity, they come ashore to the same area where they were born to lay their eggs. Female sea turtles use the Earth's magnetic field and other cues to guide them home to continue a life cycle that has been occurring for more than 100 million years.