Nants ingonyama bagithi Baba, Sithi uhm ingonyama… (Lion King – opening scene ;)) Ok so there may be no Pride Rock or Elton John involved, but the sea turtle life cycle is very long with many different hurdles from the moment a turtle lays her eggs until her offspring can reproduce.
So let’s start at the very beginning (a very good place to start!): the female turtle will crawl onto the beach after dark and will start the nesting process. Once she has located her desired nesting site she will start to dig her nest. Using her powerful front flippers she will start to carve out a big pit, the body pit. Once satisfied she will then use her back flippers and carve out a cylindrical egg chamber as deep as her back flippers can reach (up to a massive 1 meter – 3 ft – depth). When she can dig no further she will lay between 100-150 eggs in the chamber. On completing her laying, she will then cover the eggs with her back flippers and then will use her front flippers to cover her pit and camouflage the nest. She then returns to the sea and will continue to nest a further 3-6 times within the season, but she will never see her offspring again. The eggs will remain incubating in the sand for 50-70 days before the hatchlings will emerge. Unlike you and me turtles do not have an X and Y chromosome and the sex of the hatchlings is determined by the temperature in the middle 3rd of the incubation phase. Temperatures of 28°C (82°F) or below produces all male offspring, 32°C (90°F) or above produces all female and 30°C (86°F) produces a mixed sexed clutch. Once they have hatched baby turtles will orientate themselves towards the ocean using the reflection of the stars and moon off the sea's surface (there are issues with development on the beaches misorientating hatchlings away from the water, but we will tackle this subject in an upcoming blog J). They will swim out as far as they can, known as the 2 hour hatchling frenzy, until they are picked up by the ocean currents. While they are in this frenzy they will not eat anything as they have their yolk sac - a packed lunch, which they have absorbed during development, sustaining them until they are out of immediate danger. They will then drift with the currents out into the open ocean where they will remain for a period of time which has not yet been identified and thus the phase is know as the 'lost years', where they hide within floating debris or Sargassum grass using it as a shelter from predators and feeding off the fish larvae, algae and plankton that are found under these habitats. After several years floating in their shelter, juveniles will migrate back to coastal waters when they are about the size of a dinner plate, where they adopt several specific feeding (foraging) sites. As we learnt last week, green turtles are true herbivores and will feed in the shallow lagoons, whereas the loggerheads and hawksbills will feed off-shore on coral reefs. Juveniles will not return to their natal site but reside in the areas where the currents distributed them, meaning that juveniles from distant natal areas live together until they reach adulthood. Upon reaching adulthood, 20-25 years later, males and females will migrate thousands of miles from their foraging grounds to their natal breeding grounds. Because of the vast distances covered in travelling, adults will typically only make this voyage every 2-3 years. When they reach the breeding grounds, courtship takes place approximately one month before the before the nesting season, and can be with multiple males. Once courtship has taken place the female stored enough sperm to fertilize her clutches for the season, and when it is time she will make her way to the very same beach on which she originally hatched and will lay her nest, thus the cycle is complete. And that’s the cycle in a nut shell. A staggering 20-25 years before a single female can start to reproduce. That’s a long time to try and survive for and we will touch on the threats to sea turtles in the next blog, and what’s even more astounding is we still do not know how long they can live. One of life’s little mysteries!
There’s just enough time for a quick anecdote (Anniedote – she’ll be proud of me!) if I may which highlights the massive span of time these individuals have before they can reproduce. My mum grew up for a period of time in Northern Cyprus and the turtles that she saw hatching on the beach are quite possibly some of the same turtles that I have been monitoring in my years of volunteering in Cyprus… Now that is also the circle of life! J
Until the next time folks!