Turtles

What are Turtles?

© Thomas P. Peschak from his book Lost World; The Marine Realm of Aldabra & The Seychelles

© Thomas P. Peschak from his book Lost World; The Marine Realm of Aldabra & The Seychelles

Turtles are large reptiles that live in tropical and sub-tropical waters throughout the world. They breath air and are cold blooded. They spend most of their lives in the seas and oceans but female turtles will come up onto beaches to nest and lay eggs. Turtles are one of the oldest reptile groups. Turtles have changed very little in the last 70 to 100 million years.

Species

There are seven living species of sea turtles: flatback turtle, green turtle, hawksbill turtle, Kemp’s ridley turtle,leatherback turtle, loggerhead turtle and olive ridley turtle. All species except the leatherback are in the family Cheloniidae. The leatherback belongs to the family Dermochelyidae and is its only member.

Click on the photo below to learn about the Hawksbill Turtle…

Hawksbill Turtle © WiseOceans/Abbie Hine

Hawksbill Turtle
© WiseOceans/Abbie Hine

Do you want to work with turtles? Visit our Wise Work page!

Distribution

Most species of turtle have a world-wide distribution; being found in all oceans except for the polar regions.  Some species travel between oceans. The flatback sea turtle is found solely on the northern coast of Australia.

Green Turtles © Christian Loader

Green Turtles © Christian Loader

Diet

Turtles feed on a wide range of animals and plants. They are mostly omnivorous in their adult life, except the green turtle which is herbivorous, changing from a carnivorous diet when young. Some species specialise on certain prey; sea sponges are the principal food of hawksbill sea turtles, constituting 70–95% of their diets in the Caribbean. Leatherback turtles feed almost exclusively on jellyfish and help control jellyfish populations.

Habitat

Turtles are generally found in the waters over continental shelves. After taking to the water for the first time, males will not return to shore again. During the first three to five years life turtles spend most time in the pelagic zone floating in seaweed beds (The “lost years”). Green turtles in particular are often found in Sargassum beds, a brown seaweed in which they find shelter and food. Once the turtle has reached adulthood it moves closer to the shore. Females will come ashore to lay their eggs on sandy beaches during the nesting season.

For more than 100 million years turtles have covered vast distances across the world’s oceans, performing a vital and integral role in marine and coastal ecosystems. Over the last 200 years human activities have tipped the scales against the survival of these ancient mariners. Urgent global action is needed to ensure their future. (WWF)

Importance to ecosystems
Turtles play key roles that are critical to them as well as to humans:
  • © Thomas P. Peschak from his book Lost World; The Marine Realm of Aldabra & The Seychelles

    © Thomas P. Peschak from his book Lost World; The Marine Realm of Aldabra & The Seychelles

    In the oceans, turtles, especially green turtles, are one of very few creatures (manatees are another) that eat the sea grass that grows on the sea floor. Sea grass needs to be constantly cut short to help it grow across the sea floor. Turtles act as grazing animals that cut the grass short and help maintain the health of the sea grass beds. Sea grass beds provide breeding and developmental grounds for numerous species of fish, shellfish and crustaceans. Without sea grass beds, many marine species humans harvest would be lost, as would the lower levels of the food chain.

  • Beaches and dunes form a fragile ecosystem that depends on vegetation to protect against erosion. Eggs, hatched or unhatched, and hatchlings that fail to make it into the ocean are nutrient sources for dune vegetation. Turtles use beaches and the lower dunes to nest and lay their eggs. As the dune vegetation grows stronger and healthier, the health of the entire beach/dune ecosystem becomes better. Stronger vegetation and root systems help to hold the sand in the dunes and help protect the beach from erosion

It is estimated that 1 in 1,000 turtle hatchling reach adulthood!

© Helping Kenya

© Helping Kenya

Conservation status and threats
Of the seven species of turtles, all are listed on the IUCN Red List of Endangered Species as either “endangered” or “critically endangered”. Globally, the Kemp’s ridley, hawksbill, and leatherback turtles are listed as “Critically Endangered”, the loggerhead and green as “Endangered”, the olive ridley as “Vulnerable” and the flatback as “Data Deficient”, meaning that its conservation status is unclear due to lack of data. Although sea turtles usually lay around one hundred eggs at a time, on average only one of the eggs from the nest will survive to adulthood. While many of the things that endanger these hatchlings are natural, such as predators including sharks, crabs, raccoons, foxes, and seagulls, many new threats to turtle are due to humans.

Say no to plastic bags!

1356103564Threats to turtles include:

  • Threats to nesting: artificial lighting, beach disturbance, hazards on the beach
  • Oil spills and marine pollution
  • Litter, especially plastic
  • Poaching
  • Entanglement
  • By-catch & destructive fishing practises
  • & many more

Respiration

Turtles are almost always submerged, and, therefore, have developed an anaerobic system of energy metabolism. Although all sea turtles breathe air, under dire circumstances they may divert to anaerobic metabolism for long periods of time. When surfacing to breathe, a sea turtle can quickly refill its lungs with a single explosive exhalation and rapid inhalation. Their large lungs have adapted to permit rapid exchange of oxygen and to avoid trapping gases during deep dives.

Turtle fact: 
Female turtles often return to the beach they were born on to lay their eggs!!

Reproduction & Nesting

© WiseOceans/AbbieHine

© WiseOceans/AbbieHine

Turtles will reach maturity from about 25- 30 years onwards.
After mating at sea, adult female turtles return to land to nest at night. They make from one to eight nests per season. The mature nesting female hauls herself onto the beach, nearly always at night, and finds suitable sand on which to create a nest. Using her hind flippers, she digs a circular hole 40 to 50 centimetres (16 to 20 in) deep. After the hole is dug, the female then starts filling the nest with a clutch of soft-shelled eggs one by one until she has deposited around 50 to 200 eggs, depending on the species. Some species have been reported to lay 250 eggs, such as the hawksbill. After laying, she re-fills the nest with sand, re-sculpting and smoothing the surface until it is relatively undetectable visually. She then returns to the ocean, leaving the eggs untended.

© WiseOceans

© WiseOceans

Incubation takes about 60 days. The eggs in one nest hatch together over a very short period of time. When ready, hatchlings tear their shells apart with their snout and dig through the sand. Again, this usually takes place at night. Once they reach the surface, they instinctively head towards the sea.

Instead of nesting individually like the other species, Ridley turtles come ashore en masse, this is known as an “arribada” (arrival). With the Kemp’s ridley sea turtles this occurs during the day.

The Seychelles is one of the only places in the world where hawksbill turtles will come up the beach to nest and the hatchling will return to the sea during daylight.  This makes them very vulnerable to dehydration and predators.

Turtle fact: Turtle gender depends on sand temperature while the egg is incubating. Lighter sands maintain higher temperatures, which decreases incubation time and results in more female hatchlings.  In other words, the warmer the sand more females – the colder the sand more males!!

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Turtle life cycle