~ Sea Turtles ~
Sea turtles are perfectly adapted for life in the oceans. They are large long-lived animals (50 to 100 years?) with relatively streamlined shells.
The swimming limbs are held out to the sides more than downwards, making movement on land very difficult and awkward. The front flippers are generally elongated and provide the main propulsive force. The hind flippers are large and spadelike and the females use these when digging their nests in the sand.
Sea turtles absorb a great deal of salt from their diet and when they drink sea water they have salt glands in their eye sockets which enables them to excrete excess salt. The salt concentration can be twice as much as in sea water. When female turtles nest they are said to cry, but in reality, they are excreting salt from the glands in their eyes.
Sea turtles feed in a variety of ways although all hatchlings are carnivores, eating slow moving animals near the surface. The adults are essentially carnivores though stomach contents often include vegetable matter. Each species has its own food preference but all tend to be opportunistic. Food ranges from bottom dwellers such as crabs to floating jellyfish. Green turtles are herbivores, feeding on sea grasses, algae and mangrove shoots.
There is some evidence that young sea turtles can confuse oil droplets for food and that some
adults eat plastic bags mistaking them for jellyfish. Ingesting pollutants is a cause of many fatalities in sea turtles.
It may take 15-30 years for marine turtles to reach sexual maturity. All sea turtles have very similar life-histories, mating taking place in coastal waters and the females returning to the beaches where they were born to lay their eggs. Most species lay about 100 eggs in a flask shaped hole in the sand. Depending on the species, they may lay 2 - 6 times in a season although they may not lay again for 2 - 4 years.
The female turtles usually go ashore at night, dig their nests and then lay about 100 soft shelled eggs, which look similar to ping pong balls. The eggs are then covered with sand and left to hatch. The nests are about 45 cm deep. The eggs must remain undisturbed in the warm sand for approximately 55 days before hatching. If the temperature goes above 28 degrees celsius the eggs will hatch as females, below this temperature males will hatch. Although females lay thousands of eggs each summer, very few hatchlings survive to adulthood.
Together, the hatchlings dig their way out of the nest. Usually emerging at night, the group makes its way down the beach and enters the sea. This race to the sea is important for the hatchlings' biological cycle.
A real danger for baby sea turtles are the lights near beaches (street, parking, and building lights) which disorientate them, causing the hatchlings to wander in the wrong direction. When this happens they will die of dehydration or be eaten by predators. This migration to the sea is made more difficult by vehicle tracks and sand pits made during the day by tourists. The turtles are too small to climb out and soon die of dehydration in the hot sun of the morning. For approximately 3 days the hatchlings swim directly out to sea to escape shore based predators, then they begin to feed on passing morsels of food. It is believed that they drift with the currents, but little is known of hatchling and pre-adult turtles.