The life of a Green Sea Turtle

 (This was written as a college paper on populations, compatibility an life history and can be used as such)

     The mother Green Sea Turtle works her way ashore at French Frigate Shoals in the NW Hawaiian islands(3). This is her second time coming ashore this season to lay a clutch of eggs. Green Sea Turtles can lay up to 9 clutches per season(2). As she comes ashore at night she finds the spot for her nest. Coming ashore at night helps to protect against predators and protects mother and eggs from the sun. Using her fins, she digs a “body pit”(2) and positions herself for the work of digging the nest for the eggs. Her hind flippers will dictate the depth of the pit. Working methodically and tirelessly, she digs out a hole. She can deposit anywhere from 50 to 200 eggs per clutch(2). Once she has deposited her eggs, she carefully covers the nest and returns to the sea. It will take 45 to 70 days for the eggs to incubate and hatch.

     A male sea turtle uses its caruncle, a temporary tooth, to slice open it’s flexible eggshell. It is summer time and the siblings of the sea turtle are also freeing themselves. This is the first population this young turtle will belong to. Sea turtles in general are solitary creatures(2). In this stage of its life, the population will help to ensure his survival. Hatchlings can take 3 to seven days to dig out of the nest(2). Since daytime hours are dangerous for the young turtles, due to predators and drying out by the sun, the population depends on the fastest digger. The hatchling closest to the surface can feel if the sand is hot or cool indicating day or night. Once it senses that night has fallen, it climbs out followed by a group of its siblings(2). Density-dependent regulation(1), the ability of a species to control its population through physiological or behavioral changes, is demonstrated here in that the number of hatchlings leaving at any one time increases the survival percentage while accounting for a possible 90% loss in the population of hatchlings(2). Should all of the hatchlings survive, nesting would become almost impossible since sea turtles return to their place of birth when they become adults. In this way, nature has given the turtles a manner of species survival and population control.

     As the hatchlings move towards the water many are lost. Nests that have not been destroyed by predators will produce hatchlings that must make a long trek to the sea. Those not taken by predators on the land face predators at sea. Some hatchlings can become disoriented by artificial light and move towards it instead of the sea and fall victim to cars or simply die of exposure(2). The young male turtle struggles on towards the sea. Reaching the surf he rides the under tow out to sea. He then begins a swim frenzy(2) that will last 24 to 48 hours continuously, taking the young turtle farther out to sea. Once at sea, the young turtle becomes an individual, separated from his siblings that have survived. He must now make his way in the world.

     Young Green sea turtles are carnivorous(3), but will grow into vegetarians. The young male sustains himself on crustaceans and jellyfish. The first year of his life is a mystery, being a complete loner and staying out at sea. He will hide in seaweed patches to avoid predators giving him time to out grow all his predators save for large sharks and killer whales. This life-history trait(1) is still not completely understood, since no one is sure what happens in these early years we can only assume and speculate on what happens. Regardless, this trait has served the turtle well since sea turtles have been around since the age of dinosaurs and have seen them disappear while they still survive.

     As time passes and the turtle matures, he becomes part of the sea environment and enters a new population. Small fish will feed on the algae growing on his back. This will create a mutualistic symbiotic relationship(3). He is also a vegetarian now and must forage among reefs and in shallows making him a part of these communities as well. He even occasionally finds himself foraging in the shallows with other sea turtles that have congregated where the food is abundant. In this instance, he becomes a part of the turtle population for a time. He will do so again when it is time for him to mate.

     Time has passed and the male has reached sexual maturity. His carapace is 31 inches in length and he is about 50 years old. Upon finding a female he begins courting her weeks before copulation. This will be one of the few times that he will interact with others of his species. He may have to compete with another male at some time, but for now he is the only suitor. Once impregnated, the female will return to her “natal beach”(3) to nest and lay her eggs. The male will return to his life until the next season. Sea turtles can have a reproductive life of up to 30 years(2). Should he live that long, he will eventually pass away of old age. Unfortunately, he will most likely become the victim of a predator or get caught in a fishing net or ingest garbage that will take his life. Regardless of how he dies, it will still be as an individual, separated from his kind by nature’s design and yet still a part of the sea’s population.

     In the life of a sea turtle, we see the components of population, life history and the individual over a long period of time. From the frantic pace of birth and the struggle for survival, to the slow pace a maturation and the return to the place of birth to continue the species. The population controls set by nature have served the turtle well. With little social activity, the population has survived and outlasted other species. The adaptations have used the population to ensure survival of the species through reproductive life span, clutch size and the instinct hardwired into the hatchlings. The individual then has the adaptation of being carnivore and then herbivore thus reducing the chance of food depletion. The solitary life also seems to serve the turtle well in that competition and territoriality is reduced. In these ways, the sea turtle provides excellent examples of population dynamics, life-history adaptations and individual importance.

(1) A Primer for Environmental Literacy, Frank B. Golley

(2)  Seaworld.Org

(3)  Earthtrust.Org