Turtles
Testudines
INDEX
WHAT ARE TURTLES?
TYPES OF TURTLES
TURTLE FEATURES
TURTLE REPRODUCTION
WHERE DID TURTLES COME FROM?
TURTLES, MAN AND CONSERVATION
TURTLES OF THE BAHAMAS
THE TORTOISE THAT ONCE ROAMED THE BAHAMAS
TURTLES OF ARDASTRA GARDENS
WHAT ARE TURTLES?
Turtles are reptiles and like all reptiles they are cold blooded, have scaly skin, lay eggs and breathe with lungs. What sets the turtles apart from all other reptiles is their characteristic shells. The term “turtle” is used to describe this group of reptiles that includes both the turtles and tortoises. They are found in a variety of habitats including the sea, rain forests and even the desert. They are most abundant in the tropics but they are quite abundant in temperate regions and have also been recorded in Arctic waters.
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TYPES OF TURTLES
There are a total of 260 species of turtles that are placed in the order Testudines. This order is divided into two groups depending upon how the head can move.
- Peurodira (side-necked) - the neck vertebrae flex laterally, allowing the neck to bend and pull the head in side-ways. There are a total of two families in this group.
- Cryptodira (hidden necked) – the neck vertebrae flex vertically, allowing the neck to be drawn straight back within the shell. There are nine different families in this group.
Most species are freshwater turtles, also known as terrapins, which literally means semi-terrestrial. Some turtles live on land (terrestrial) and are known as tortoises. A small number live in the sea, these are the marine turtles. Typically the freshwater species have a more streamlined body with a flatter shell and webbed feet. Tortoises have a high dome-like shell and thick stocky legs made for walking.
TURTLE FEATURES
Interesting shell
Turtles are unmistakable thanks to their shell. All turtle shells have a top and bottom, the top is known as the carapace and the bottom is known as the plastron. The shell is not an “exoskeleton” and the turtle cannot slip in and out of its shell as seen in many cartoons. The shell is actually part of the backbone and ribcage, which have been modified to encapsulate nearly all of the turtle’s body. Even the shoulder and hip joints are inside of this backbone and ribcage structure, unlike any other vertebrate on earth. This shell is then covered by enlarged scales, made of keratin, just like the fingernails of humans. This shell has been proven to not only add protection to the turtle but also be an extra source of calcium when needed. For example, some hibernating species use the alkaline properties of the calcium in the shell to buffer the acids that build up during the hibernating process; similarly, reproductively active females rely on the extra calcium in their shells to help make shells for their eggs.
How to breathe like a turtle?
Turtles breathe with lungs that are located inside of a rigid ribcage and therefore they rely on a slightly different mechanism for inhaling and exhaling air. The leg muscles are involved in the inflation of the lungs and the muscles on the top and bottom of the lungs work together to exhale the air. However, many turtles supplement gas exchange from the lungs with gas exchange in the throat and even the cloaca region (anal cavity), which helps these animals to remain under the water for hours at a time.
Different ways of eating
Turtles are herbivorous (plant eating), carnivorous (meat eating) and omnivorous (plant and meat eating). The majority are omnivorous but many have highly specialized diets. For example the Leatherback feeds only on jellyfish and the Hawksbill turtle feeds on sponges. All of these specialized diets have produced an array of different beaks. Firstly, turtles do not have teeth. Instead, they have a hard casing similar to the beak of a bird. This beak is self-sharpening and is good for eating a variety of things.
Some turtles use this sharp beak to chomp and tear leaves. Some turtles have a hooked tip to allow them to grab and hold slippery foods such as fish or jellyfish.
Some turtles chase their food whereas some turtles are ambush predators.
Some turtles have mouths that work more like a vacuum cleaner and they suck their prey into their mouths.
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TURTLE REPRODUCTION
Turtles take a long time to reach sexual maturity, usually between 10 and 50 years. Although some turtles may live in water and some on land, all turtles lay eggs on land and usually buried in soil, sand or rotting vegetation. Turtles do not tend to the eggs or the young in any way; the young are nidifugous (hatch well developed and totally independent). Many turtles lay hundreds of eggs per clutch, however, a couple of species only lay one or two eggs. Many turtles, particularly sea turtles, are known to lay more than one clutch in a single year.
The sex of the young is determined by the temperature of the eggs while they are incubating in the ground. This is called Temperature dependent sex determination (TSD). For the majority of animals on the planet, the sex is determined by genes. For example, the genes (or sex chromosomes) that determine sex in humans are: XX (females), XY(males). All turtles (except for two species in the mud turtle family) lack sex chromosomes all together and rely on the environment to determine the sexes. Interestingly, the sex is determined by two different patterns depending upon the species. In some species males are produced at low temperatures and females at high ones. Whereas some species females are produced at high and low temperatures and anything in between produces males.
After about 45-90 days, the young will hatch from the egg with the help from an egg tooth on the top of their beak. Once hatched, the young must be careful, as they are potential food for many birds, mammals and reptiles. In most cases only one turtle from each clutch will survive to become a mature adult.
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WHERE DID TURTLES COME FROM?
Turtles have been around since the beginning of the dinosaurs (at least 280 million years). These earlier turtles had teeth, which eventually became a self-sharpening beak by about 150 million years ago. These turtles also had smaller shells, which did not cover the whole body and as dangerous predators began to appear, the turtles began to develop larger shells to protect their heads. About 200 million years ago the first “side-necked” turtles appeared and later came the “hidden neck” turtles, which are the majority of turtles living today. The latter did not descend from the “side-necks” but rather the two groups came up with a solution to the same problem.
Turtles had their peak in diversity around 100 million ears ago when the largest turtle that ever swam the ocean also lived. This turtle has been named the “King turtle” and was about 20 feet long and 12 feet wide.
Turtles have changed very little since the time they first appeared and they have certainly proven themselves to be very adaptable.
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TURTLES, MAN AND CONSERVATION
Turtles have survived for millions of years, their shells being the only protection they needed. Today they need protection from people. Geological records show that hominids (human ancestors and their relatives) have been eating turtles for at least 2 million years and therefore have had a severe impact on these animals, causing the extinction of many different forms, especially the tortoises and sea turtles.
Turtles are hunted for several reasons. Their shells have been used to make jewelry and ornaments, their skin to make small leather goods, their meat and eggs for food, and their fat for oil. As they become more rare in some parts of the world, their products become more profitable and therefore they are targeted even more. Sea turtles often fall victim to fishing nets, pollution and coastal development.
Today, most turtles are protected under international laws which has helped to slow the decline of many species. However, many countries do not enforce the international laws at the local level and therefore some countries still hunt these critically endangered animals.
TURTLES OF THE BAHAMAS
There are two major types of turtles living in the Bahamas today, freshwater turtles and marine turtles.
- Freshwater turtles
The West Indies has four native species of freshwater turtles all in the genus: Trachemys, and two of which occur in the Bahamas. As fresh water turtles are popular as pets, other species have also made their way into the West Indies as careless owners release their exotic pets into the wild. Here we will look at the species native to the Bahamas.
Cat Island slider
(Trachemys terrapen)
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Endangered species
This freshwater turtle is found in the Bahamas and also in Jamaica (also known as the Jamaican slider). It has long been debated as to whether this turtle originates from the Bahamas or Jamaica, and the debate is sure to go on for quite some time. Even though the popular theory was that these turtles originated from Jamaica, current geological evidence may suggest that they were in the Bahamas long before the native Indians first came to these islands. There is also evidence from archeological sites on San Salvador that the native Indians ate these turtles and transplanted them around the West Indies.
This turtle is found on many islands in the Bahamas. Namely, Eleuthra, Exuma, Andros, Paradise Island, New Providence and 60% of the Bahamian population is found on Cat Island, hence the name. However, on certain islands where exotic turtle species are brought in as pets, populations are being diluted as the exotic species and native species interbreed.
Inagua slider
(Trachemys stejnegeri malonei)
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Endangered species
This turtle is a subspecies of the Central Antillean Slider and is endemic to Great Inagua. The Inagua slider has one of the most restricted ranges of any other turtle as it is only found on the Eastern most portion of Inagua. These turtles are in great danger of becoming extinct. Even though the people living on the island of Inagua do not eat turtles, the island does not have much fresh water on it. Typically this island receives very little rainfall and the majority of the island is occupied by a large saline lake called Lake Windsor. These turtles spend most of their time therefore hiding out on land awaiting rain. Today there is even less freshwater on the island due to development in technologies which enables the pumping of freshwater from natural reserves for the people living there. The mid 1900’s saw a major expansion of the saline lakes for the salt producing industry which may have contaminated past freshwater habitats. Today the majority of freshwater habitats where the Inagua slider lives is associated with development, such as roads, dikes and the airstrip. These areas are at risk from further development and are not safe areas for such a critically endangered species. The majority of Great Inagua is protected as a national park; however, the majority of the Inagua slider population is not found inside the park.
- Marine sea turtles
The West Indies has 6 known marine sea turtles of which 5 are found in Bahamian waters. The first three described below are the most commonly encountered marine turtles in the Bahamas.
Green turtle
(Chelonia mydas)
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Endangered species
Loggerhead turtle
(Caretta caretta)
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Threatened species
Hawksbill turtle
(Eretmochelys imbricata)
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Endangered species
Leatherback turtle
(Dermochelys coriacea)
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Endangered species
Olive ridley turtle
(Lepidochelys olivacea)
THE TORTOISE THAT ONCE ROAMED THE BAHAMAS
Somewhere between 10-20,000 years ago the Bahamas had a large tortoise living in its forests. Back then the Bahamas was quite a different place. The sea levels were very low and so many of the islands were joined together, covered in a very diverse and lush forest. In this forest roamed a three-foot tall tortoise, one of four different species to have once roamed the West Indies. These are the relatives of the smaller South American Red-footed tortoise (Geochelone sp.) which lives today.
The fossils of this tortoise have been discovered on the islands of Andros, New Providence and Abaco as well as the Turks and Caicos and parts of the Caribbean. There is evidence suggesting that these tortoises lived in these regions for a very long time and being one of the largest herbivores of these islands, they must have played an important role in seed dispersal. Many of the upper region fossils were charred, suggesting that they were cooked and eaten by the native peoples of that time.
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TURTLES OF ARDASTRA
Ardastra has red-eared sliders in the ponds and Yellow footed tortoises on exhibit.
Red-eared slider
(Trachemys scripta elegans)
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Threatened species
The red-eared slider is a freshwater turtle, which originates from the Mississippi River Valley. These turtles are generally omnivorous, the young being carnivores and the adults become more herbivorous as they mature. They are extremely popular in the pet trade and because of this, they have found themselves all over the world. As these turtles can reach about 11 inches long and live to about 20 years of age, pet owners often get fed up with them and release them into the wild where they can have negative effects on the native ecology systems. The freshwater turtles found in ponds on Paradise Island and New Providence tend to be hybrids of the native terrapins and Red-eared sliders. Ardastra has received countless Red-eared sliders, which have outstayed their welcome in many homes across the Bahamas. Unfortunately Ardastra cannot accept anymore of these turtles and would like to see a ban on the import of this species into the country to help conserve the native varieties.
Yellow-footed tortoise
(Geochelone denticulata)
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Threatened species
Yellow-footed tortoises are originally native to Northern South America, but now have established populations on many Caribbean islands. Usually found in dense humid forests, these tortoises feed on grasses, succulents and fallen fruits. They are often confused with their close relative, the Red-footed tortoise, as both can have either yellow or red scales on their legs. DNA must often be used to determine between the two species.
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