About Sea Turtles
Species of Sea Turtles
A Little Information on Turtles
Turtles are reptiles and a part of the Order Testudines which includes all turtles and tortoises. The most distinctive trait of this group is the protective shell. Also, like all reptiles, turtles have lungs and scaled skin. The shell is made up of two main parts. The ribs and backbone of turtles are fused to the top shell. The top shell is referred to as the carapace. The lower shell is called the plastron. These two bony parts are connected on the sides by cartilage. A layer of keratin (the same substance as your finger nails) covers both shells. The only species of sea turtle without this type of shell is the leatherback. Their shell is cartilaginous (like your ears and nose). The shape and characteristics of the shell are variable between different members of the Order Testudines.
Sea turtles have a number of adaptations for life in the ocean. The shell of sea turtles is flattened to increase their ability to swim quickly. Their legs are elongated into paddle-like flippers. These two changes make it impossible for a sea turtle to “hide” or retract body parts inside their shell. Instead of hiding, speed and agility are used to out maneuver fast predators like sharks or whales.
Reproduction Cycle of a Sea Turtle
During the breeding season, male and female sea turtles come together and mate offshore. The males mount the females in the water and internally fertilize the eggs. Later, the female swims closer to shore and begins looking for a good place to nest. She walks ashore into the soft sand and excavates a body pit. Once this is complete, she begins to scoop sand with her rear flippers in an alternating fashion. The female digs a rounded, flask-shaped hole with a narrowing neck. The amount of eggs deposited in the nest depends on the species and size of the female. On average, 50-180 leathery shelled eggs are laid. The eggs incubate for 48 to 62 days depending on the beach temperature. The eggs are tightly 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.
The hatching process occurs over a couple days. Once the hatchlings have absorbed their yolk sac, they crawl upward toward the warmer temperature of the surface of the sand. The 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. As they scurry across the sand, predators including ghost crabs, vultures, seagulls, raccoons, coyotes and feral dogs predate many of the hatchlings. The hatchlings “imprint” on the beach as they walk out into the water. This refers to their ability to remember that specific beach and return to it as an adult sea turtle.
Once the baby turtles enter the water, they swim aggressively toward the origin of the waves, surfacing approximately every two minutes to breathe. Less than 1% of the hatchlings will survive their first year. Many animals in the water like crabs, fish, sharks and whales eat 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. Then, once the sea turtles reach maturity the cycle will begin anew. Depending on the species of sea turtle, it can take 15-40 years to reach maturity.
Sea Turtle Navigation
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 cues, or "star maps." Perhaps a combination of these theories explains how sea turtles navigate.
Interesting Sea Turtle Links
An informative sea turtle webpage - Seaturtle.org
U.S. Fish & Wildlife Sea Turtle Brochure. Download the PDF.
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.