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  Sea Turtles
Click on each turtle's name or photo for more information
Pacific Black Sea Turtle
Pacific Black
Chelonia agassizi
En Español
Kemp's Ridley
Lepidochelys kempii
En Español
Kemp's ridley sea turtle

Flatback sea turtle

Flatback
Natator depressa
En Español

(Photo by: Jarrad Sherborne)

Leatherback
Dermochelys coriacea
En Español
Leatherback sea turtle
Atlantic green sea turtle

Atlantic Green
Chelonia mydas
En Español

click here for satellite track

Loggerhead
Caretta caretta
En Español
Loggerhead sea turtle
Hawksbill sea turtle
Hawksbill
Eretmochelys imbricata
En Español

Olive Ridley
Lepidochelys olivacea
En Español

(Photo by: Kedar Gore)

Olive ridley sea turtle
 
     
 

Exactly what is a turtle? En Español
Turtles belong to an ancient group of vertebrate (backboned) animals called reptiles. Fossil turtles date back to the Triassic Era some 100 million years ago. The most obvious characteristic of this group of reptiles is the presence of protective shell. The shell is composed of three parts -- an upper shell, or carapace, attached to the lower plastron by a bony bridge.

Turtle ribs are outside of the girdles of the limbs and do not hinder movement of the legs. The ten dorsal vertebrae are expanded and fused with the carapace. There aren't any sternal ribs or sternum.

The Basics
Instead of teeth, turtles are equipped with a horny bill.

All turtles belong to the order Chelonia (or Testudinata). This large group is subdivided into two major groups. One group, the Cryptodira, are able to draw their head and neck into their shell for protection. The Pleurodira, or side-necked and snake-necked turtles are not able to do this, but instead turn the head and neck to the side.

Turtles, like all reptiles, are cold blooded (ectothermic). Their body temperature is the same as their surroundings. All present day turtles lay eggs. The land living tortoises produce hard-shelled eggs like a chicken, while others like sea turtles lay eggs with a leathery or parchment-like shell.

Names
Several non-scientific names are used for turtles. The term "tortoise" in North America is used for high-domed, land living turtles with elephant-like legs and feet. In England and Australia, the term tortoise is applied to water living turtles. Biologists use scientific names, unique to each plant or animal species worldwide, to avoid this type of confusion. Another pesky term is "terrapin." In the United States, the term terrapin is reserved for the diamondback terrapins of the genus Malaclemys. These turtles live in coastal marshland and are comfortable on land or in shallow water.

The common name 'turtle' is applied to the more aquatic types, including: musk turtles, mud turtles, snapping turtles, sliders and the subject of this book, the sea turtles. Sea turtle limbs have evolved into flippers and their body shape is streamlined (aquadynamic) or torpedo shaped.

Growth Rate
A turtle's growth rate is determined by the temperature of its body and amount and frequency of food availability. Some sea turtles are herbivores while others are carnivores. The giant leatherback feeds primarily on jellyfish and the hawksbill prefers sponges.

Mating & Reproduction
Sea turtles typically mate at sea a few weeks prior to nesting and only the females come ashore to nest. With the rare exception of occasional basking by male olive ridley's (Lepidochelys olivacea) or the Australian flatback sea turtle (Natator depressus), male sea turtles virtually never come ashore. Sea turtle females excavate a body pit and then begin digging the next cavity, using alternating scoops of their hind flippers. Depending on the species and size of the female, they then deposit 50-180 leathery-shelled eggs. These eggs will typically incubate from 48 to 62 days, depending on nesting beach temperatures. The eggs are close packed and in contact with one another. Metabolic heating within the nest helps to speed up the hatching process in the final stages of incubation.

Imprinting
For many years sea turtle biologists have stated that female sea turtles return to their natal beach to lay their own clutches of eggs. This ability to return to their own hatch site is called imprinting. In recent years, genetic research has proven this hypothesis to be true. Individual turtle populations are genetically distinct. But how are sea turtles able to navigate great distances from their normal feeding grounds to their nesting grounds?

Navigation
Sea turtle hatchlings usually emerge from their underground sandy nests under the cover of darkness. Then, when a majority of hatchlings are on the surface, they make a synchronized frenzied rush to the awaiting surf through a gamut of predators including ghost crabs, raccoons, coyotes and feral dogs. Scientists have demonstrated that hatchling turtles crawl toward the horizon and that they are able to detect subtle differences in light intensity. Artificial light sources like automobiles or street lights close to hatchling beaches tend to disorient the babies and many die as they crawl away from the ocean and onto roads and highways. According to biologists Salmon and Lohmann (1989), once in the water, the hatchling turtles orient toward the direction of the waves. Dr. Kenneth J. Lohmann has recently made a strong case for the turtles having a built-in magnetic compass which enables them to orient themselves using earth's magnetic field to guide their long distance marine journeys. Placing newly hatched loggerhead sea turtles in a circular experimental tank, Dr. Lohmann mechanically reversed the magnetic field, causing the turtles to swim in the opposite direction. Dr. David Owens of Texas A&M University likewise has made a strong case for turtles responding to a particular water chemistry through their sense of smell (olfaction). Yet, other biologists believe that sea turtles utilize celestial, or "star maps." Perhaps a combination of these theories explains how these turtles are able to navigate their way back home some 15 to 40 years after they hatched.

Once the baby turtles enter the water, they swim aggressively toward the origin of the waves, surfacing approximately every two minutes to breathe.

Young Sea Turtles
Regardless of the species of sea turtles, no one knows where the young spend the first year of their lives, or "the lost year." Many biologists speculate that they float in and among rafts of sargassum weed, feeding on the rich variety of small creatures that seek refuge in it. Only a small percentage of baby turtles will survive to become adult animals and make their homeward journey to perpetuate their kind.

Interesting Sea Turtle Links

  • The Anatomy of Sea Turtles by Jeanette Wyneken, PhD. view the book.
  • A selection of informative video clips are available at the NOAA website. View video page
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