Life Cycle

Breeding season for sea turtles starts in May and last hatchlings hatchs from the their nest in September. A female make 3 to 4 nest in a nesting season. Male turtles leave the nesting beaches just after mating.

Marine turtles mate in coastal waters, lagoons or in lakes two weeks before nesting (April-May). Occasionaly, only one of the three emergences from sea ends up with succesful egg-laying and the others are 'false crawls' to find a suitable nesting place and to facilitate the egg movement through the body.They choose a site where the tidal waves will not affect on the nest and they move very slowly on land. The period of incubation lasts about two months. The young hatchlings hatch in a 1-2 days of time and wait underneath the ground until night, and then they dig their way to surface. After reaching the surface, the young hatchlings start on their journey to the sea. They use the reflection coming from the sea. And it's seen that most of the hatchlings move to different directions in the photo polluted areas. Affects by artificial lights may lead to a fatal effect on hatchlings. Their sexually mature is at the age of 25-30 years. Therefore, we do not have much information about their sexual maturity during this period of time in their natural life. Fishing nets, incidental captures, speed boats have negative effects on their life.

Diet

Green and black sea turtles have finely serrated jaws adapted for a vegetarian diet of sea grasses and algae. In adulthood, they are the only herbivorous sea turtles, but in an aquarium environment all sea turtle species can be maintained on a carnivorous diet. Loggerheads' and ridleys' jaws are adapted for crushing and grinding. Their diet consists primarily of crabs, mollusks, shrimps, jellyfish, and vegetation. A hawksbill has a narrow head with jaws meeting at an acute angle, adapted for getting food from crevices in coral reefs. They eat sponges, tunicates, shrimps, and squids. Leatherbacks have delicate scissorlike jaws that would be damaged by anything other than their normal diet of jellyfish, tunicates, and other soft-bodied animals. The mouth cavity and throat are lined with papillae (spinelike projections) pointed backward to help them swallow soft foods. Researchers continue to study the feeding habits of flatbacks. There is evidence that they are opportunistic feeders that eat seaweeds, cuttlefish, and sea cucumbers. Some species change eating habits as they age. For instance, green sea turtles are mainly carnivorous from hatchling until juvenile size; they then progressively shift to an herbivorous diet.

Migration

Adult females migrate to their natal beach and lay eggs in the sand. Hatchlings undergo a short but high-risk, due to predators, journey to the shoreline, and then swim to the open ocean. Initially their swimming direction is oriented into the waves; near shore the waves provide an indication of the direction of the open ocean. Their migration then continues for hundreds or thousands of kilometers into the ocean, into favorable feeding grounds. Turtles may actually use the geomagnetic field to tell them their location (of course, the open ocean has no landmarks); if this is the case, then their magnetoperception system seems to work on a more refined level than that of birds, which is thought to provide directional but not locational information. Some scientists think that sea turtles probably use the geomagnetic field to orient their swim in the deep ocean, but they would also have celestial cues available to them. The directional vector of sea turtles is probably determined genetically, although their is no data to support this assumption. Also intriguing but unexplained is their ability to find their way precisely back to their natal beach over their vast travel distance.

Sex Determination

Temperature both influences sexual differentiation and rate of development of Caretta caretta. As it does with many other chelonian species, within the limits of embryonic tolerance cooler temperatures produce male hatchlings (26 and 28°C, C. caretta; 26°C, C. mydas), and warmer temperatures produce female hatchlings (32°C, C. caretta; 29 and 32°C, C. mydas) and the temperatures between these produce both sexes. The phenomenon of temperature dependent sex determination has important consequences in conservation practices. The middle one-third of the incubation period (stages 22-27) is the sex determining period for C. caretta. Prior to stage 21, the embryonic kidney is not differentiated into a functional mesonephros and there is no visible gonad. Thus, within this critical period, incubation temperature has a particular influence on the growth of urogenital tissue. The rate of embryonic development is faster at the warmer temperatures. A variety of factors (maternal behaviour in choosing a nest site, the zygote's response to temperature in becoming male or female, environmental effects (temporal or spatial temperature of the nesting area) interact to determine the sex ratio. Temperature dependent sex determination (TSD) has been reported in at least five families of Chelonians(7 genera, 72 species). There are three pattern of TSD. -Type A; females produced at lower temperatures, males produced at high temperatures (most crocodilians and lizards). -Type B; females produced at high temperatures, males at lower temperatures (many turtles). -Type C; females produced at low and high temperatures, males at intermediate temperatures(three crocodile, one lizard, and three turtle species).