Sea Turtle Biology

//Sea Turtle Biology

Sea Turtle Biology

INTRODUCTION TO TURTLES

Sea turtles are reptiles and come under the group of Chelonians, this also includes land tortoises and fresh water terrapins. Currently there are approximately 12 families, 90 genera and 250 species in the Chelonians group

  • Sea Turtle Biology
    • They are Marine Reptiles – their body temperature is determined by their environment
    • They Air Breathing – at rest they can hold their breath for up to 2hrs, and 20mins while active and foraging
    • Ever growing – Their shell and body grows for their entire life. All Sea Turtle hatchlings hatch at a size not much bigger than a match box.  For their first 5yrs of life they have a growth spurt of up to 5cm a yr, after approximately 10yrs of age they slow to around 1cm a yr
    • Long lived
  • Species
    • 7 Species (Size descending): Leatherback, Green, Loggerhead, Flatback, Olive Ridley, Kemp’s Ridley and Hawksbill.
    • There are mainly Hawksbills and Green Turtles here in Raja Ampat but there are also Leatherback nesting sites
  • Life cycle
    • Mating – times of year June to September
    • Nesting – Season is approximately from July to October
    • Hatching
    • The ‘Lost Years’ – From Hatchlings to Juveniles
    • Juveniles/sub-adults
    • Adults
  • Habitats through life cycle
    • Hatchling – open water
    • Juv/Sub-adult – shallow, food rich reefs/grass beds
    • Adult – Feeding grounds/mating grounds/nesting sites – Migrations
  • Behaviour
    • Swimming
    • Feeding / Foraging
    • Resting – UW or on the Surface
    • Breathing

 

Sea turtles are one of the few species that live in the seas but nest on land, crossing that land and marine division is a place not many animals hold, making them the ambassadors of the Sea’s.  Breathing air limits turtles in that they always need to come to the surface to breath.  However, they can hold their breath for up to three hours when resting.  Often, they will hold their breath between 20-40mins depending on their activity level during each dive.  This ability gives them plenty of time to hunt while under the water.  Most Sea turtles are carnivores and have a wide diet including, jellyfish, tunicates (ascidians, and sea squirts), sponges (Hawksbill sea turtles are one of the few animals to eat sponges), soft corals, crustaian (crabs and shrimps and prawns), Molluscs (squid, and octopus), and a number of fish species.  The green turtles however are vegetarians and feed on sea grasses and algae as adults, as hatchling and juveniles, as well as the sea grass and algae they will also eat some crustians and molluscs.

Turtles are built for the marine environment, where they are graceful, fast and agile.  On land, they are slow and clumsy heaving their weight about.  Look at their land relatives you can see the changes turtles have undergone to adapt to life in water, their feet have elongated and become fins, with their front fins providing the power and speed and their hind fins work as rudders.  Their shells have flattened and become more streamlined enabling them to glide through the water.

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Turtles role in the environment

Raja Ampat is quite possibly the richest coral reef system in the world; it is an Archipelago of more than 1500 Islands, Islets cays and shoals, all around four main Islands Misool, Salawati Batanta and Waigeo, in total there are 612 Islands covering an area of 40,000km²/15,000sq mi, with a land area covering 8,034km²

Hawksbills and Greens are the most commonly sighted Turtles in the area.  There have been sightings of Leatherbacks and Olive Ridleys.  The area provides nesting grounds for all four species, the Leatherbacks are known to nest on Papua on two main beaches called Jamursba medi and Warman in the Sausapor district, these two beaches alone make up about 75% of the total number of nests laid in the west Pacific, this is the largest remaining Leatherback nesting population in the Pacific.   Islands as well as Hawksbills.  There have been very few Green Turtles Nests with the closest to us being on Waigeo.

Sea Turtles play a very important role in their relation with their environment.  They can act like miniature reefs providing a mobile home for many parasites and other animals such as remoras.

Green sea turtles are like the gardeners of the sea, trimming the sea grass and keeping it healthy, allowing new shoots to grow increasing the productivity of the grass bed.  A vital role in the maintenance of the worlds Sea Grass beds.  If sea grass beds were left unattended they become over grown and water circulation stops throughout the bed, this allows the growth of slim mold which in turn kills the sea Grass and the whole system collapses.  Sea Grass beds are vitail home for many marine animals, especially juvenile fish.  They also fix large amounts of carbon and produce large quantities of oxygen vital to all life on earth.

Hawksbills play an extremely important role in the maintenance of the reefs ecosystem.  If left unattended the sponge populations on many reefs would bloom competing with the hard corals for space and taking over the reef.  Hawksbills role is vital to keep the natural balance of the coral reef, as sponges have a toxic coating it make them inedible to many animals.  Hawksbills are not affected by this toxin.  They’re not the tidiest of eaters leaving many broken fragments that other creatures can now receive nutrients from.

Nearly all species of Sea Turtle eat Jelly fish.  As we know jelly fish have stinging tentacles that capture prey often in the form of juvenile fish.  If Sea Turtles were not there to eat and control the jelly fish populations there would be such a bloom in the numbers of jelly fish that fish population stocks would be severely damaged.  A leatherback sea Turtle can eat up to 200kg of jelly fish as day.

Range

Sea turtles can be found in all the temperate seas and oceans around the world.  Divided into populations it has been over the recent years with DNA and genetic research that scientists are seeing that there are a number of genetically independent groups of sea turtles.  For example, the Loggerhead sea turtles found in the Mediterranean are genetically different and hold different blood values to the pacific or Atlantic populations.

Over the years with satellite tagging and Genetic studies we are learning more and more about Turtles and their travels some have been recorded to travel great distance between feeding and nesting grounds.

Its in water data and observations that are now vital to help build a better picture of what each population is doing in each area.  By recording their size and sex (if distinguishable) and behavior it will help build a better picture of what the different marine areas are to the Turtles and it will help support better protection methods for them in these areas.

Raja Ampat was declared a Turtle sanctuary in 2012, however little to no monitoring or protection is taking place for these beautiful creatures.

Our aim is to record as much information as we can every time we see a Turtle, where we see it, what’s it doing and hopefully identify if it is a turtle we have seen in this area before.

There are more and more methods being developed to identify individual turtles.  It was not that long ago discovered that the pattern of the scutes on the sides of the heads of green turtles is distinct to each individual like a finger print.

It has not yet been determined if this is the case with other species but the more pictures that can be taken and the more information gathered the better it will be to determine if this is the case.

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Sea turtle biology

Sea turtles are one of the oldest animals on our plant, having been in existence for nearly 100 million years, their ancestors Santanachelys can be found in many fossil records dating back 112 million years.  Today there are eight species of sea turtle inhabiting the world’s oceans, however more than 100 different species have been described from the fossil record.  Marine turtles in the main are much larger than their land dwelling relatives, they have lost the ability to completely retract their heads into their shells.  Their feet have become fins with the extension of their digits to form a paddle propelling them through the water.  Their shells have become compressed and streamlined for gliding through the water with more ease, and flattened hind limbs that act like rudders to control direction.  All sea turtles retain the need to breath air and are reptiles.  The largest species of marine turtles the leatherback it can weight over 500 kg, their forelimb span can measure over 3m and be over 2m in length.  They can have very long lifespan if they make it to becoming an adult as with all sea turtles

Life cycle

Their life cycle is a long one and full of many predators, dangers habitat loss and nesting ground destruction.  Mating takes place in the water where the males use their front and hind fins to hold onto the females.  Copulation can take between 3-7 hours and turtles will need to come up for air numerous times during the process.  Females may mate with multiple males, all of which will contribute to the overall clutch size.  30 days after mating the female will heave herself out of the sea and onto a beach to lay her eggs, which can take up to 2 hours. For

Hawks bills turtles the depth of a typical nest from the surface of the sand is about 30 to 40cm, 90 to 100 cm for green turtles. An egg is very similar in size and dimension to a ping pong ball.

Hatching typically occurs between July and August, inclusive, once laid it takes 45 to 60 days (depending on the temperature of the nest chamber) for the eggs to incubate and begin hatching.  During this period, there are threats of predation from foxes, badgers, weasels, dogs, and parasite infestation can destroy nests.

Furthermore, human placed sun beds on the beach can, if placed over a nest, block out the all important heat needed to incubate the clutch beneath the surface of the sand.  Sun umbrella poles can break through into the nest chamber breaking eggs within.  Heavy pressure, including passing vehicles and horses, can also damage the eggs below.

During the incubation period the sex of the baby turtles is determined by the temperature. High temperatures lead to all females (32°C), cool temperatures result in all males (26°C). Equal split of sex is at around 29°C to 30°C.  When ready the first hatchlings break out of their eggs and they wait in the sand below the surface for night fall.  It can take up to 5 days before the entire nest has hatched.  It can take 2 to 3 days for the hatchling to reach the surface of the sand from the egg chamber, this time is critical as enables the egg matter on to the hatchlings to dry out and rub off in the sand, reducing its smell and therefore reducing the risk of a predators smelling them while they run along the sand towards the sea.  Each hatchling has a long and dangerous journey ahead it, with predators in the form of foxes, boar, cats, dogs, seagulls and ghost crabs before they even enter the sea.  Once in the sea the list of predators becomes much longer, anything that can catch or bite the vulnerable hatchling is a potential predator.  From here on is a grey zone in the life of the turtle as very little is known about them until they reach adulthood.  It takes 20-30 yrs for turtles to reach full maturity and return to the beach and nesting grounds from which they once first entered the sea all those years ago.  It is thought that the hatchlings head to open waters, where they hide underneath floating seaweed clump and flotsam and jetsam.  Sadly, not many turtles make it to adulthood. From a typical egg the chances of it reaching maturity is less than 0.5-0.3%, in other words 3 in 1000 eggs may make it to full maturity.

Adult sea turtles typically live in coastal areas to feed or to breed.  Often this can involve huge distances, up to thousands of miles, in order to migrate from feeding grounds to breeding areas.  Where the lifecycles begins a new with the next generation.

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Behavior

Sea turtles are one of the few species that live in the seas but nest on land, crossing that land and marine division is a place not many animals hold, known as eco-transformers.  Breathing air limits turtles in that they always need to come to the surface to breath.  They may also spend time at the surface resting or to bask in the sunlight during the cooler months.  Often this is around the coastline where they can run a high risk of being hit by a boat.  They can however hold their breath for up to three hours when resting.  Often, they will hold their breath between 20-40mins depending on their activity levels during their dive. This ability gives them plenty of time to hunt and feed while under the water.  Most Sea turtles are carnivores and have a wide diet including, jellyfish (a favourite of the caretta), tunicates (ascidians, and sea squirts), sponges (turtles are one of the few animals to eat sponges), soft corals, crustaian (crabs and shrimps and prawns), Molluscs (squid, and octopus), and a number of fish species.  The green turtles however are vegetarians and feed on sea grasses and algae as adults, resent research has shown that often adults will only eat either sea grass or algae As hatchlings and juveniles, as well as the sea grass and algae they will also eat some curstians and molluscs.

Turtles are built for the marine environment, where they are graceful, fast and agile.  On land, they are slow and clumsy heaving their weight about.  When you look at their land relatives you can see the changes turtles have undergone to adapt to life in water, their feet have elongated and become fins, with their front fins providing the power and speed and their hind fins working as rudders.  Their shells have flattened and become more streamlined enabling them to glide through the water, this flattening has led to the loss of the ability to retract themselves into their shells.  However, they still hold the instinctive behaviour to pull their heads back, you may often see that when a turtle is surprised or scared by something the instinctively pull their heads towards their shells, the neck retracts in the head meets with the carapace ad plastron.

Often there is a misconception that turtles are just cold blooded reptiles.  If you have the privilege to spend time among these creatures you will see that each of them has their own character, food preference and querken behaviours.  Some are bold and inquisitive, while others can be shy and receding.

To learn more about sea turtles and have to opportunity to meet them face to have a look at our Sea Turtle Ecology Speciality 

Biodiversity is running a Sea Turtle monitoring program

By | 2017-05-29T14:16:56+00:00 April 10th, 2017|Turtle conservation|0 Comments

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