Basics of Sea Turtles
Sea turtles are large, air breathing reptiles that inhabit tropical and subtropical seas throughout the world. Their shells consist of an upper (carapace) and a lower part (plastron). Hard scales, or scutes, cover all but the leatherback, and the number and arrangement of these scutes can be used to determine the species. A Sea Turtle’s life may cross many of the worlds oceans.
Sea turtles come in various sizes, shapes and colors. The Olive Ridley, for ex
ample, is usually less than 100 pounds, while the Leatherback typically ranges from 650 to 1300 pounds! The upper shell, or carapace, of each sea turtle species ranges in length, color, shape and arrangement of scales.
Sea turtles do not have teeth, but their jaws have modified “beaks” suited to their particular diet. They do not have visible ears, but have eardrums covered by skin. They hear best at low frequencies, and their sense of smell is excellent. Their vision underwater is good, but they are nearsighted out of water. Their streamlined bodies and large flippers make them remarkably adapted to life at sea. However, sea turtles maintain close ties to land, where they began their lives as hatchlings.
Sea Turtle’s Reproduction
Only females come ashore to nest, males rarely return to land after crawling into the sea as hatchlings. Most females return to nest on the beach where they were born. Nesting seasons occur at different times around the world. In the U.S., nesting occurs from April through October. Most females return to nest at least twice during each mating season; some may nest up to ten times in a season. A female will not nest in consecutive years, however; they typically skip one or two years before returning.
When the females nest, it occurs most often at night. The female crawls out of the ocean, pausing frequently as if carefully scoping out her spot. Sometimes she will not crawl out of the ocean, but for unknown reason
s decide not to nest. This is called a “false crawl”, and it can happen naturally or be caused by people on the beach (Conserve Turtles, 2015).
The female turtle crawls into a dry part of the beach and begins to fling away loose sand with her flippers. She then constructs a “body pit” by digging with her flippers and rotating her body. After the body pit is complete, she digs an egg cavity using her cupped rear flippers as shovels. The egg cavity is shaped roughly like a teardrop and is usually slightly tilted.
When the turtle has finished digging the egg chamber, she begins to lay her eggs. Two or three eggs drop out at a time, while mucus is being secreted. Because the eggs are flexible, they don’t break as they fall into the chamber. This flexibility also allows both the female and the nest to hold more eggs. The average size of a clutch (group of eggs that are laid) ranges from about 80 to 120 eggs, depending on the species. Once all eggs are in the chamber, the mother turtle uses her rear flippers to push sand over the top of the egg cavity. Gradually, she packs the sand down over the top and then begins using her front flippers to refill the body pit and disguise the nest. By throwing sand in all directions, it is much harder for predators to find the eggs. After the nest is thoroughly concealed, the female crawls back to the sea to rest before nesting again later that season or before beginning her migration back to her feeding ground. It’s extremely important that the female turtle does not feel as if it is in danger; some turtles (while rarely) will abandon her nest.
Incubation takes about 60 days, but since the temperature of t
he sand governs the speed at which the embryos develop, the hatching period can cover a broad range. Essentially, the hotter the sand surrounding the nest, the faster the embryos will develop. Cooler sand has a tendency to produce more males, with warmer sand producing a higher ratio of females.
Baby sea turtles deserve a lot of credit; hatchlings must break out of their shells and flee to life all on their own. To break open their shells, hatchlings use a temporary, sharp egg-tooth, called a “caruncle”. The caruncle is an extension of the upper jaw that falls off soon after birth. Digging out of the nest is a group effort that takes several days. Hatchlings usually emerge from their nest at night or during a rainstorm when temperatures are cooler. Once they decide to burst out, they erupt from the nest cavity as a group. The little turtles orient themselves to the bright horizon, and then dash toward the sea.
If they don’t make it to the ocean quickly, many hatchlings will die of dehydration in the sun or be caught by predators like birds and crabs. Once in the water, they typically swim several miles off shore, where they are caught in currents and seaweed that may carry them for years before returning to nearshore waters.
There are many obstacles hatchlings face in the open ocean; sharks, big fish and circling birds all eat baby sea turtles, and they die after accidentally eating tar balls and plastic garbage. The obstacles are so numerous for baby turtles that only about one in 1,000 survives to adulthood.
It’s theorized that turtles spend their earliest, most vulnerable years floating around the sea in giant beds of Sargasso weeds, where they do little more than eat and grow. Once turtles reach dinner-plate size, they appear at feeding grounds in nearshore waters. They grow slowly and take between 15 and 50 years to reach reproductive maturity, depending on the species. There is no way to determine the age of a sea turtle from its physical appearance. It’s theorized that some species can live over 100 years.