The sea turtles have been here for over 250 million years, the archaeologists have found so many clues supporting this. Turtles are cold-blooded, they have had a shell that protects them. The lower portion of the shell is called the Plastron. These sea turtles are found all over the world and inhabit almost every type of climate. The average lifespan of a sea turtle can vary from 30 to over 100 years depending upon the species. There is a lot to know about the life cycle of a sea turtle. There are over 7 species of sea turtles, which are as below
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Hawksbill
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Olive Ridley
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Kemp’s Ridley
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Flatback
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Leatherback
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Loggerhead
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Green Sea Turtle
Each of these sea turtles has its own life cycle. Let us now focus on the family as a whole instead of the individuals.
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Stage 1(the Eggs)
Every 2 to 4 years pregnant mothers crawl on the beach, bury a pit in the sand and lay their eggs. They come anywhere between dust and dawn laying anywhere between 100 to 200 eggs per nest. They will lay several nests for the course of the season. They cover up the pit and head back to sea and after 6 to 12 weeks we will see baby turtles cracking the shell wailing out of the sand and flapping their flippers across the beach. The sea turtles eggs incubate in the sand for 45 to 50 days depending upon the species of the turtle. During this time the temperatures of the nest determine whether the hatchlings will be male or female. Although this seems to be nice, 99% of these turtles don’t make it to adulthood. Most of them will perish in this tough journey ahead.
Stage 2(Hatchling)
Hatching is an exhausting process for baby turtles. After breaking out of their shell they must dig their way out of the nest then cross the sea into the ocean. All of this requires frequent breaks, so these baby turtles typically weigh until night when there are fewer predators(you can say when the predators are least likely to attack) and the sand is cool enough to crawl across. Once they are through the sand they look for one signal, i.e. the faint reflection of the moon of the ocean. This behavior is innate, there is no thinking but an instinct. It’s the hatchlings’ urge to head towards the light, as that leads them towards the ocean. The artificial lights can confuse the hatchlings, the lucky ones who don’t get fooled crawl as quickly as they can towards the sea hoping predators don’t get the best of them. Even when the hatchlings are in the ocean you may think everything is good, but the ocean is not that safe either. The moment the hatchlings touch the water it begins the friendsy period. There is nothing but 24 hr straight swimming. You can imagine a living creature being the size of the palm of your hand being dropped into the ocean 10 minutes after birth and now you have to swim and not stop. If you stop here you’re dead, if you don’t stop you are dead as well. The shallow water is filled with creatures that love to eat a tender hatchling.
Stage 3(Small Juvenile State)
This is the stage where the research is scarce. As if you imagine trying to put a tracking device on a baby sea turtle that would transmit signals, which would never run out of a battery and doesn’t fall off. Doing all of this while not affecting the turtle’s bouncy or the ability to swim might be very difficult. As a result, these years are called the lost years. With our growing technology, these years are becoming more known to us now. It is clear that the turtles use currents to their advantage. It was first thought to be passive migration, which is unintentionally following the currents. But the evidence shows that sea turtles actively orient themself and swim. The best of the research shows sea turtles deduct earth’s magnetic field and they use it as a compass, an accurate one to navigate the oceans. The complexity of this goes beyond the scope, it is important to understand that the sea turtles have a sense we don’t have called Magnetoreception. This sense becomes very important for turtles later in their life.
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Stage 4(Large Juvenile State and Sub Adult State)
Once the turtles reach this stage they head to the feeding grounds in coastal waters. These feeding grounds may be over 10,000 km from their home beach. It takes from over 10 to 20 years for the turtles to reach maturity depending upon the species. It is estimated that less to 10% of the turtles that hatch reach maturity. In the feeding grounds, these large juvenile adults turn into sub-adults. The sea current will help the turtles reach their feeding habitat. Each of the turtles carries a york that can supply them with nutrients for a little while, but when it is gone they will have to find their own food. Once these turtles reach a suitable feeding habitat, sea turtles will reside there until they grow to become an adult. Sea turtles have varying diets depending upon what age they are and what species it is.
Stage 5(Mature Adult State)
Juvenile and adult sea turtles will often eat seaweeds, seagrass, and algae. They also eat small animals like jellyfish, shrimp, sea sponges, snails, molluscs, and crabs. The feeding habitat and breeding habitat are usually far away. The distance usually depends on the population of the turtles. An adult sea turtle can mature between 30 to 40 years. So in these terms, we can say it takes a period of 30 years for a sea turtle to return back to their home which they remember it all this time.
Stage 6(Mating Season)
In the feeding grounds, once these sub-adult turtles are ready to mate with their mature adults, this will be the time to start migrating back to their nesting site. These migrations can be over 1000 km. During this migration period, the male turtle will meet as many females to pass-on as much as his DNA as he can, While a female turtle will store as much sperm as she can. This is because more fertilized eggs mean more offspring, which in turn means more survivors. When in water the sea turtles slow their heart rate in order to preserve their oxygen underwater. The heartbeat is said to be slower like 9 min per beat. After mating males turtles go back to the feeding grounds whereas the female’s turtles continue to the beach. At the beach, the females lay the eggs and the cycle continues. The soon to be mothers travel back to the feeding grounds until the next mating season. The interesting fact is the mothers lay their eggs in the exact same beach where they were born. This phenomenon is called natal homing and how it works has not been fully understood. The best explanations which they have come up with would be Geomagnetic Imprinting. When they are born the hatchlings imprint on the magnetic field of the earth and use this unique signature to guide them back home decades later. But the question remains why to go back to the exact same beach, as to travel 10000 km just to reproduce doesn’t seem ideal. During this journey, they are risking death, expending tons of energy. Even though there are perfectly good nesting sites close by. It may be due to natal homing must have some kind of benefits or outway the risks for the turtle to adopt this kind of behaviour.
The process of natural selection tells us that the mother doesn’t go back to her home beach and is less likely to have her offspring survive. The mothers that stuck with what they knew worked and this tendency was passed to their young. All of it has been hardwired in its DNA to go to its home beach and the offspring have a better chance of surviving.