|
There are seven different species of sea turtle living today, and they can be found in every ocean. While certain turtles only live in limited regions, others can be found across the globe. So what are the 7 sea turtles? How do they differ from terrestrial (land-based) turtles? And just what is a scute? Read on for everything you wanted to know about sea turtles!
Living Species
There are seven species, or distinct types, of turtles currently swimming in the oceans today. They are the flatback, the green, the hawksbill, the Kemp’s ridley, the leatherback, the loggerhead, and the Olive ridley. A possible eighth species, the black sea turtle, was a source of “turtle controversy” but scientists now know that the black sea turtle is actually a type of green sea turtle, and not a different species. All turtles are reptiles and breath air, but sea turtles do differ from their land-based cousins. Sea turtles like the greens, leatherbacks, and loggerheads are found in warm ocean water world wide, but some species are only found in certain, small regions of the world. The flatback resides solely along the northern coast of Australia, while the Hawksbill is found primarily in tropical reef habitats of the Caribbean and Australia. The Kemp’s ridley sea turtle lives in the western North Atlantic Ocean, while its close relative the Olive ridley lives in the Pacific. Green sea turtles (Honu) are a common sight in the Hawaiian islands, but they are not the only turtle native to our waters; the hawksbill and leatherback are also seen here.
Turtle Biology
Of course all turtles have shells (which can be hard or soft), but what is a turtle shell made of? The base of the shell is actually made of bone which provides the shape and strength of the shell. The shell is actually fused to the turtle’s backbone and ribs, forming one solid piece. On top of the bony layer are scutes, which are large hard scales made of keratin, the same material that makes up hair, fingernails, and animal hooves. The turtle’s shell is also divided into two pieces, the carapace on top and the plastron on the bottom.
So what makes a sea turtle a sea turtle? Sea turtles differ from their cousins on land in that they have beaks instead of teeth, and flippers instead of legs. Sea turtles use their front flippers for swimming power, and females use their hind flippers for digging nests in the sand on beaches where they lay their eggs. Sea turtle shells are more streamlined than terrestrial turtles, meaning they provide less resistance in the water when the turtle swims, but sea turtles cannot retract their head or flippers into their shell like their cousins. Sea turtles’ eyes have adapted to see very well underwater, but their vision out of the water is quite poor (the opposite of how human eyes work well out of the water, but not so well underwater without a mask; this is due to the different densities of water and air and how they affect the passage of light). Ocean-dwelling turtles also have a special gland next to their eyes that secretes salt in the form of “salty tears.” Living in salt water means the turtle consumes a lot of salt when it eats or drinks, so this gland is very important as it gets rid of extra salt and maintains the turtle’s internal water balance.
The diet of sea turtles depends on the species. Some are vegetarians (greens and flatbacks) and eat algae and seaweed while others prefer to eat jellyfish (loggerheads, hawksbills, and leatherbacks) or crustaceans like shrimps, clams, and mollusks (loggerheads). The hawksbill turtle uses its specially curved beak to eat sea sponges, its food of choice, even though some of the sponges it eats are highly toxic to other animals. The ridley sea turtles are omnivorous, meaning they eat both plants (algae and sea grasses) and animals (shrimp, crabs, fish).
Sea turtles can grow to be quite large, depending on the species. The smallest sea turtles are the ridleys, which grow to about two feet in length and weigh about 100lbs. The biggest sea turtle is the leatherback which can be up to 7-feet long, and weigh up to 1300 pounds.
Turtles in Danger
Turtles have the reputation of being slow. And while sea turtles may be able to swim quite quickly (certainly faster than you or I), they grow very slowly. A female turtle is not ready to lay eggs for many years, sometimes not until she is 35-40 years old. And even when she is ready, of the hundreds of eggs she is lays each breeding season, only a few will result in baby turtles that survive and make it to sea. Because of this, the total number of turtles in the ocean grows at a small rate, meaning turtle populations cannot easily recover from disturbances to their numbers. Since more turtles are dying than are being born, all 7 species are labeled as “threatened” or “endangered,” which means our help is needed to protect them. But what are the major disturbances and dangers turtles face?
Turtles, like many other animals in the ocean, are killed by the thousands each year by floating trash and debris. Some turtles will mistakenly eat garbage and choke, while others will become tangled and not be able to swim properly, making breathing and escaping predators very difficult. The same is true of fishing gear, which can accidentally trap turtles, even when the turtles are not the intended target. Fishing boats and offshore oil drilling in the Indian Ocean has been blamed for the deaths of almost 100,000 Olive ridley turtles. Turtles, even though they spend most of their lives at sea, are also at risk on land. Every sea turtle’s life begins on the beach; adult female turtles come ashore to lay their eggs in a nest she digs in the sand. Females will lay up to approximately 120 eggs per nest, and might have multiple nests each year, but they do not lay eggs every breeding season. The eggs will remain buried for close to 2 months depending on the temperature of the nest, which greatly affects how quickly the turtles develop. During this time the nest is in danger from terrestrial predators, environmental changes, and human interference. The few turtles that do hatch have an even bigger challenge ahead; they have to make the trip from the nest to the ocean and then spend years floating among sea grass beds, eating and slowly growing until they are big enough to brave the open ocean. Only about 1 in every 1000 hatchlings survive to adulthood.
Turtles are also very specific about where they nest. Females return to the very same beach at which they were born - even if that means swimming for thousands of miles across the ocean. One species, the Kemp’s ridley sea turtle, only nests on one beach in the entire world (on the coast of Mexico). Human interference at these beaches or any turtle nesting site can be catastrophic.
There is hope, however. While turtles in the Atlantic Ocean have been decreasing in number, Pacific populations have been growing. New nesting grounds have been found which indicate the turtles can adapt. Over 130,000 olive ridley’s were counted nesting at a single beach in India. And restrictions on trawling, trash disposal, and drilling are slowly making the life of a sea turtle easier. But much more needs to be done to preserve the turtles in our oceans. What can you do to help?
Trackback(0)
 |
TrackBack URI for this entry
Subscribe to this comment's feed
Show/Hide comments
Show/Hide comment form