Diamond turtle
| Diamond turtle | ||||||||||||
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Diamond turtle ( Malaclemys terrapin ), female |
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| Malaclemys | ||||||||||||
| JE Gray , 1844 | ||||||||||||
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| Malaclemys terrapin | ||||||||||||
| ( Schoepf , 1793) |
The Diamondback Terrapin ( Malaclemys terrapin ) is a medium-sized aquatic turtle belonging to the family emydidae that in North America the coastal area of Cape Cod , Massachusetts , in the north to Corpus Christi , Texas settled. Unlike other aquatic turtles, which are found either exclusively in fresh water or in sea water, this species is adapted to a life in salt marshes, estuaries and mangrove swamps and tolerates fluctuating salinity of the surrounding water. The diamond turtle prefers brackish water , but is also found in fresh water or marine waters.
As recently as the 18th century, this species of turtle was so numerous that it was an inexpensive staple food in some coastal areas of the United States . Today, some of the seven subspecies are considered critically endangered. In addition to fishing, habitat losses and increased hunting by predators , some of which have been introduced, have contributed to the population decline .
Appearance
Height and Secondary Sex Characteristics
Diamond turtles are medium-sized turtles; Shell length and body weight vary depending on gender and the respective subspecies.
The average length of the breastplate of male turtles when they reach sexual maturity is ten centimeters. You then weigh about three hundred grams. In the subspecies of the Texas diamond turtle living on the Texan coast, the average breastplate length of the males when reaching sexual maturity is 12.6 centimeters, while the largest male individuals have breastplate lengths of 15.3 centimeters.
The females of the diamond turtle become significantly larger and heavier. Armor lengths of 16 centimeters are the average for them. They then weigh about one kilogram. In very large females of the northern diamond turtle, such as those found off the coast of Rhode Island , the shell length is up to 22.5 centimeters.
Adult females have larger heads and shorter and narrower tails than males. When the tail is outstretched, the cloaca in males is clearly outside the area of the body protected by the shell. In females, the excretory opening is located further forward in the base of the tail, i.e. closer to the tank edge. These secondary sex differences are not yet pronounced in newly hatched and young diamond turtles. In these cases, it is not possible to determine the gender using external characteristics.
The tank
One of the specific characteristics of the diamond turtle is that the horn shields do not overlap. There is a dark, mostly ring-shaped pattern on the back shields. It is formed by the deposition of pigments during the growth phases. In this way, the age of young turtles can be determined.
The back keel running across the shell is smooth and hardly noticeable in many individuals. In young turtles and in some subspecies, this keel is more pronounced and occasionally even a little bumpy. The basic color of the carapace is very variable and ranges from a light ocher to gray-green or olive green to red-brown and almost black. The breastplate is significantly lighter than the backplate. Its color ranges from a light white yellow to a strong orange.
Other features
The rear legs of the diamond turtle are significantly larger and stronger than the front legs. Between the long and sharp claws are webbed . The strong snout is usually light, almost white in color. In some subspecies, the extremities as well as the neck and head are dotted black, in other subspecies, however, without any discoloration.
Distribution and subspecies
Diamond turtles are found from the Atlantic coast near Cape Cod , Massachusetts over the Chesapeake Bay and the Florida Keys to Corpus Christi , Texas , in the Gulf of Mexico . The distribution area extends from the moderate climatic zone to the subtropics . The 320 kilometer long Chesapeake Bay with its bay-rich coastline is considered to be the main distribution center of this turtle species. The marshes and river estuaries that are influenced by the tides are settled along this coastal strip. Today the distribution areas are disjoint. Individual subspecies can only be found in a few places.
Investigations indicate that the diamond turtles are highly localized. In studies that have been ongoing since the 1980s, in which the turtles are individually marked, they are mostly found in the same coastal bay. Only a very small proportion of the population is picked up again at a greater distance from the first site. Such local loyalty means that there is little chance that diamond turtles will naturally reintroduce themselves to coastal regions where their population was previously extinct.
There are currently seven different subspecies in diamond turtles. Genetic studies suggest that the three subspecies found on the Florida coasts are all very closely related. Further investigations can lead to a smaller number of subspecies being differentiated in the future.
- The northern diamond turtle ( Malaclemys terrapin terrapin ) is the nominate form of this turtle species. Its range extends from Cape Cod in Massachusetts to Cape Hatteras in North Carolina . The longitudinal keel of the tank is smooth. The basic tone of the back armor ranges from black to a light brown or olive. The patterns on the individual horn shields can be clearly seen. The breastplate is yellow, orange or greenish-gray in color.
- The range of the Carolina diamond turtle ( Malaclemys terrapin centrata ) stretches from Cape Hatteras to the coast of North Florida. In this turtle species there are no humps on the longitudinal keel.
- The Texas diamond turtle ( Malaclemys terrapin littoralis ) occurs from the west coast of Louisiana to the west coast of Texas. The longitudinal keel has slight humps in the direction of the tail. The breastplate and the top of the head are light in color.
- The peacock diamond turtle ( Malaclemys terrapin macrospilota ) lives on the west coast of Florida. With her, the longitudinal keel has pointed humps. The horn shields are from yellow to orange in their respective centers.
- The Mississippi diamond turtle ( Malaclemys terrapin pileata ) is found from the Gulf Coast of Florida to the west coast of Louisiana. In this subspecies, too, the longitudinal keel only shows humps at the end. The breastplate is yellow. The top of the head, neck and legs is dark brown to black.
- The distribution area of the mangrove diamond turtle ( Malaclemys terrapin rhizophorarum ) are the Florida Keys. The longitudinal keel is very bumpy. The carapace has an elongated shape. The basic tone of the armor is brown or black. There are no markings on the neck and front extremities.
- The Miami diamond turtle ( Malaclemys terrapin tequesta ) is found on Florida's east coast. The longitudinal keel has cusps in the rear area. The horn shields are bright in their center.
habitat
The preferred habitat of diamond turtles are salt marshes as well as wide estuaries influenced by tides and in Florida also mangrove areas. Salt marshes form where sandbanks , peninsulas or island chains are in front of the coast. The water level is low, the sea water brought in with the tide washes over these marshes twice a day. After heavy rainfall, the salinity of the salt marsh can drop so much that at 15 ppt it is only half as high as that of sea water. On hot and sunny days, however, it is possible that so much water evaporates during low tide that the salinity increases to 60 ppt, which is twice as high as that of seawater. The vegetation on the salt marshes consists predominantly of salt-tolerant plants from the silt grass genus . In between there are other salt-tolerant plants from the genera Distichlis , Binsen , Iva , Samphire , Sea lavender , asters and goldenrod .
Salt marshes are often found near estuaries. Due to the tides, the water level, the temperature and the salinity of the water also fluctuate in extensive river mouths. The mangrove areas that the diamond turtle populates in Florida are subject to similar fluctuations.
Diamond turtles have adapted to this fluctuating salinity and thus developed a nutrient-rich habitat in which no other turtle species and only a few other reptiles compete with them for food. The natural scientist Ronald Orenstein therefore describes the diamond turtle as a habitat specialist. Since the diamond turtle, unlike sea turtles, depends on fresh water as drinking water, their habitat must, however, have sufficient and relatively regular rainfall.
Research in a salt marsh in Connecticut showed that the density of diamond turtles there did not correlate with the availability of food. Other factors such as the height of the tide and the density of vegetation appear to have a more important influence on whether a particular area is an ideal habitat for the diamond turtle. Another study from the 1980s suggests that the availability of suitable nesting opportunities determines whether a specific region is suitable for colonization by diamond turtles.
food
Diamond turtles eat crabs of the genera fiddler crabs , callinectus and carcinus , various types of snails , fish , mussels as well as worms, insects and carrion . They only ingest food when they are in the water. Diamond turtles are therefore mainly in search of food when the tide washes the marshes. Overall, the digestive rate is very slow and temperature-dependent.
Diamond turtles crack the shells and shells of their food with their powerful but toothless jaws. Large prey is torn apart with the claws of the front legs. Fish are only eaten occasionally as their swimming speed is usually too great for diamond turtles to hunt. However, the proportion of fish in the total diet increases when, for example, large numbers of fish species such as Menidia menidia return to the estuaries to spawn, for example , and are weakened by the act of spawning so that they can be caught by the turtles. Crabs are prey that use their claws to defend themselves against attempts by the turtles to try and cause serious injuries to the turtles. Diamond turtles therefore often only bite off one of the hind legs of larger crabs.
It depends on the distribution area which prey makes up the largest part of the food spectrum. On the coast of Virginia, diamond turtles prefer the hard-shelled snail species Nassarius obsoletus, which lives on salt plants . Diamond turtles native to the North Carolina coast mainly ate the snail Littorina irrorata . The snail species Melampus lineatus and fiddler crabs accounted for a much smaller proportion of the total diet. In Chesapeake Bay, turtles eat sand gape clams and several species of clams from the genus Tagelus , Macoma and Gemma . 83 percent of the feces of turtles living on the northwest coast of Florida consisted of remains of the shell species Mulina lateralis .
Way of life
Adaptation mechanisms to a life in salt and brackish water
Diamond turtles are able to use specific mechanisms to keep the salt concentration in their blood and other body fluids at a level that corresponds to about a third of the salinity of seawater. While in other New World pond turtles a short stay in sea water with a salinity of 30 to 35 ppt would lead to osmotic dehydration , these mechanisms allow the diamond turtle to survive in such waters for several weeks.
Diamond turtles have a salt gland behind the eye through which excess salt can be excreted. A similar gland is also found in sea turtles . The ancestry suggests that sea turtles and diamond turtles developed this gland independently of one another. The diamond turtle also excretes significantly less salt via this gland than is typical for other reptiles living in seawater. The outer skin of the diamond turtle has both low salt and water permeability.
Unlike the sea turtles, the diamond turtle depends on drinking fresh water. It is able to absorb fresh water very quickly and store it subcutaneously in the body. Diamond turtles living in freshwater therefore have a body weight that is up to twice as high as diamond turtles of comparable size that have been in seawater for longer. Their feeding behavior also differs depending on the salinity of the surrounding water. The lower the salinity, the more the turtles eat and thus avoid consuming high amounts of salt.
Diamond turtles living in brackish or sea water drink off the thin layer of fresh water that is then on the surface of the water after rainfall. This freshwater film is usually thinner than two millimeters. To get to the water, the turtles swimming on the surface of the water bend their necks so that their mouths are level with the film. Diamond turtles have also been observed to pick up raindrops with their mouths open during rain or to drink drops of fresh water on the body of fellow species.
Adjustments to temperature fluctuations
The diamond turtle is unable to maintain its body temperature through metabolic activities. Your body temperature and thus your activity spectrum are essentially determined by the ambient temperature.
At water temperatures below 15 degrees diamond turtles stop eating and at water temperatures below 13 degrees they go into hibernation . The hibernation of the diamond turtles living on the Cape Cod coast lasts from October through April and is the longest observed by diamond turtles. According to the current state of knowledge, however, the diamond turtles that live on the southern coast of Florida do not hibernate.
The detailed functioning of hibernation in diamond turtles has not yet been adequately investigated. For example, it is not known whether the hibernation is triggered by the drop in temperature or the reduced availability of food and how the turtles avoid dehydration during their long hibernation due to an increase in the salt content in their blood and other body fluids. The likelihood of the diamond turtles surviving hibernation does not appear to be affected by whether they hibernate in fresh or brackish water.
Diamond turtles usually hibernate in bays that are exposed to the tides. An investigation of the wintering sites on the coast of Cape May , New Jersey , found turtles in the bottom mud in places that were between 1.5 and 2.5 meters below the water level during low tide. While most of the turtles hibernated individually, animals that hibernated collectively were also found beneath the undermined bank slopes. Some of the 311 turtles found had buried themselves in the muddy embankment between 15 and 50 centimeters deep. During the hibernation, the entire metabolism of the turtles is greatly slowed, so that they can go without food for several months. They are also able to tap some of the oxygen in the water via the cloaca.
In addition to winter dormancy, diamond turtles are also able to go into arid or heat rigor. For this, too, the turtles burrow into the sediment and thus survive longer periods of heat with little precipitation. This form of summer dormancy can be observed especially in the diamond turtles living on the southern tip of Florida.
Outside of winter dormancy, diamond turtles reach their optimal body temperature by sunbathing. Occasionally they go ashore to do this. More typical, however, are sunbathing, in which they float on the surface of the water with their front and rear legs spread wide apart. The sunbathing also helps to reduce any algae or fungus growth on the shell.
Reproduction
Mating behavior
Little is known about the mating behavior of the diamond turtles. All findings are based on a few studies and the observation of a small number of mating animals. The main mating season is late spring, although diamond turtles can be seen later in the year during the mating act.
The turtles gather in certain bays during the main mating season. It is not yet known what factors trigger these gatherings. Females ready to mate float on the surface of the water. Approaching males first sniff the females' cloacal region and then mount the female. The pairing only takes a minute or two. Females can store semen for several years. If they mate with several males, the eggs of one clutch can have different fathers. It is known from turtle farms that female diamond turtles laid fertilized eggs four years later without having had contact with a male.
The clutch
Females can lay more than one clutch per year. Up to five clutches per year have been counted in captive diamond turtles. In the wild, two to three clutches seem to be the normal number.
For oviposition, the females use sandy areas that are largely free of vegetation and that are above the high tide marks. The clutch density can be very high on stretches of coast where only a few places are suitable for laying nests. At a breeding site on Rhode Island, 446 clutches per hectare have been counted. The females generally return to the same racks every year.
If suitable racks are located far from the marshes, there is a risk that the females will become dehydrated or overheated on the way to the racks. The females are largely protected from being stalked by predators because their armor color allows them to blend in with their surroundings. Once the female has found a suitable spot, she needs about 30 minutes to dig the nest pit. First, the selected area is smoothed with the snout and front legs. The diamond turtle then digs a hole up to 24 centimeters deep with its hind legs. The actual clutch chamber in which the eggs are located is on average 4.7 centimeters deep and 7.3 centimeters wide. How deep the clutch chamber is below the surface of the earth influences the hatching rate. In nests that are too shallow, the upper eggs do not develop, and in too deep nests no young hatch from the lower eggs. The optimal depth for a clutch seems to be 18 centimeters. After laying, the female covers the eggs with the excavated sand in such a way that the place cannot be distinguished from the rest of the environment.
The eggs are whitish to slightly pink and oval. Their shells are soft and therefore not very fragile. The shells only harden within the first 24 hours, but are always a bit more robust than bird eggs of the same size. The clutch size varies depending on the geographical distribution. Diamond turtles tend to lay smaller clutches in the south of the range. In Florida the average clutch size is 6.7 eggs, while in Chesapeake Bay it is 12.3 eggs. Barbara Brennessel assumes that in the climatically more favorable regions it pays off for the turtles to lay several small clutches. In the north, on the other hand, the time window in which a turtle clutch can mature is much smaller and it is therefore more promising for the turtle's reproductive success to create a few clutches with a larger number of eggs.
The average incubation time for a clutch is between sixty and ninety days. The time it takes for a young turtle to hatch from an egg depends on the ambient temperature and humidity.
Gender ratio
The sex of hatching diamond turtles is determined by the ambient temperature of the clutch. This temperature-dependent sex determination is characteristic of most turtle species. Under laboratory conditions only males hatched from clutches that were kept at a temperature below 28 degrees. If the temperature was consistently above 30 degrees, mostly female diamond turtles hatched. In the wild, the clutches are subject to greater temperature fluctuations. The temperature fluctuations an individual egg is exposed to depends on its relative position within the clutch. The eggs on the top of the clutch are exposed to greater temperature fluctuations than those on the bottom.
The sex of newly hatched turtles cannot be determined by external characteristics. This either requires complex endoscopies or the young turtles have to be killed and dissected. For this reason, very little is known so far about the correlation between the ambient temperature of the clutch and the sex ratio. The natural relationship between the number of males and females is also very difficult to determine. As individual studies have shown, different numbers of males and females are caught with the same fishing method in the same region depending on the season. The death rate varies depending on the sex, depending on the area. Adult males are more likely to drown in crab traps than females because of their smaller size. On the other hand, significantly more females are run over in traffic. In areas with a high anthropogenic influence, therefore, nothing can be said about the natural sex ratio of adult animals. Attempts to farm diamond turtles commercially in the early 20th century, however, know that the highest reproductive rate was achieved with a ratio of one male to five females.
The young turtles
Young diamond turtles, like many other turtle species, have an egg tooth at the end of their snout . It consists of a keratin thickening that disappears within a few weeks. With this egg tooth they cut open the egg shell.
The hatching time of a clutch is in autumn and can extend over several days. Some young animals even prefer to leave the nest pit only after hibernation. This does not increase your chances of survival: After the first hatch, the probability increases that predators will find the clutch and eat the turtles that are ready to hatch. Young turtles that leave the nest usually immediately seek cover under low-lying plants. They are then about the size of a one-euro coin and weigh five grams. Very little is known about the first years of life of the diamond turtle. However, young diamond turtles tend to stay in parts of the salt marshes closer to the coast and use shallower water zones than the adult animals.
Young diamond turtles with a body weight of less than 50 grams are less able to adapt to the high salinity of the surrounding water compared to adult turtles. Studies suggest that before reaching this weight, they will develop best when the salinity is around 8 ppt. In the wild they usually do not reach this body weight before the end of their first year of life and sometimes not until the age of three. Little is known about the growing up of the young turtles, however, and there are a number of indications that suggest that the turtles mostly hide on land under salt plants during the early stages of their growth.
Reaching sexual maturity
Diamond turtles reach sexual maturity the earlier the further they live in climatically favorable regions. For reaching the respective sexual maturity, the height reached is more decisive than the age. Since the annual growth phase of the diamond turtles living in the north is shorter than that of the south due to the temperature, they are usually older when they reproduce for the first time.
Females of the southern diamond turtle occasionally breed as early as four years of age, while the females living on the Cape Cod coast are nearly ten years old before they lay eggs for the first time. Males of the diamond turtles living in the south can reproduce from their third year of life, while in the north the males are between five and eight years old before they mate with a female for the first time.
Age
Turtles are known for their long life. It has been proven that individual individuals of certain turtle species lived between 160 and 200 years. However, these record holders are exclusively land-living turtles. In the case of the turtles that live in water, it is assumed that their maximum age is significantly lower.
For the diamond turtle, there is not yet sufficient data available to allow conclusions to be drawn about its maximum age. Marking individual individuals did not begin until the early 1980s. Since some animals were already sexually mature at this point in time and still show no physical limitations when they were found twenty years later, the life span of the diamond turtle is currently estimated at forty years.
Duration
Diamond turtles lead a very hidden life, so that population figures are difficult to determine. The classification that the diamond turtle is now an endangered species results from two pieces of evidence. For a number of regions where there is historical evidence of diamond turtle occurrences, there are no current observations of diamond turtles. An increasing local extinction of the species is therefore assumed. This applies, for example, to the Nauset Marsh, Cape Cod, where the last diamond turtle was observed in 1976, as well as to some bays on the Atlantic coast of Florida, where the last diamond turtle was found in 1986. On Kiawah Island, South Carolina, the same fishing method as before in some bays on the Atlantic coast of Florida was only fifty instead of two hundred.
What is worrying is the observation that insufficient numbers of younger females are regrowing in a number of regions and that the population is gradually aging. Scientific studies come to the conclusion that entire age groups are missing from the population. This indicates that hatching rates have dropped significantly or that the survival rate of newly hatched turtles has changed.
The IUCN last assessed the species of diamond turtle with regard to its endangerment in 1996 and classified it as “ near threatened ”. This classification expresses that the animal species is not directly endangered in its population, but that it must be observed.
Increased pressure from predators
A full-grown diamond turtle has few predators to track it down. The clutches, newly hatched and growing turtles and the small males are particularly threatened.
Raccoons are able to detect a freshly laid clutch in the first 24 hours based on its smell. The hackers also include the red fox , the American crow and the fish crow , the North American otter , black-headed gulls , the West Atlantic riding crab and various types of rats. Raccoons have also learned to dig for eggs on suspicion in places with high clutch densities.
Newly hatched turtles are hunted and eaten by a range of birds and mammals. The fact that only a few of the young turtles survive the hatching phase can be observed in a number of turtle species. It has also been observed in other turtles that predators adapt to the hatching times. One of the protective mechanisms that young diamond turtles have developed is that they seek protection in the vegetation of the salt marshes immediately after hatching.
There is scientific consensus that predatory pressure on the diamond turtle has increased. The coastal regions in which they live regularly border areas which, because of their scenic charm and high recreational value, are popular places for human beings. The settlement density here has increased significantly over the last century. A number of predators of the diamond turtle are cultural followers of humans. The population density of the brown rat , the raccoon and some species of martens introduced into North America has increased due to the proximity of humans in the breeding areas of the diamond turtle. The drastic influence this can have on hatching success is shown by two adjacent stretches of beach on the coast of Long Island . One of the two beach sections is open to the public and is also one of the popular meeting places for young people in the evenings. The presence of humans does not prevent the turtles from making their nests and laying eggs. However, it apparently keeps away predators who plunder the fresh clutch. On the other hand, in the adjacent stretch of beach, which is not open to the public, a very large number of clutches are robbed immediately after they are deposited. In both sections, however, newly hatched diamond turtles are highly eaten by brown rats.
Similar experiences were made in the Jamaica Bay Wildlife Refuge . This small reserve is located in Queens not far from John F. Kennedy Airport in New York and consists of a number of smaller islands. Despite the poor quality of the water, there are around 2000 clutch of diamond turtles every year. This place is one of the largest known nesting places for this turtle species. However, raccoons have settled in the reserve since the late 1980s. 90 percent of the clutches are now robbed by raccoons. Occasionally the raccoons even kill the egg-laying females and eat them up.
Influences of stock by humans
From staple food to delicacy
Diamond turtles were caught in large numbers from the 18th to the early 20th centuries. Initially, they served as an inexpensive staple food that was so often served to slaves in some southern US coastal states that they went on strike. A whole cart loaded with diamond turtles could be bought for a dollar. In North Carolina, the bycatch of diamond turtles in net fishing was sometimes so high that fishermen could not bring in their nets. In the course of the 19th century, the diamond turtle gradually became a delicacy, parallel to the declining catch quotas. In the second half of the 19th century, the first course of a gala dinner consisted of turtle soup. At the White House , turtle soup was one of the preferred dishes for lunch during the presidency of William Howard Taft . They also drank champagne . Diamond turtles have even been exported to Berlin and Paris from the east coast of the USA . In the early 20th century, a dozen large diamond turtles cost between $ 96 and $ 125. The US Bureau of Fisherie has attempted to breed and raise diamond turtles on farms. It was not until the 1920s and 1930s that diamond turtles increasingly went out of fashion as a delicacy. Barbara Brennessel blames three factors for this. During the Great Depression, fewer and fewer people could afford to buy this delicacy. Preparing a diamond turtle for a soup or ragout is laborious and brutal. Some recipes call for the diamond turtle to be roasted alive in its shell. Since fewer and fewer families employed servants to whom this work could be entrusted, in the opinion of Brennessel, housewives turned to dishes that were easier to prepare. Prohibition may also have played a role. Turtle dishes are usually seasoned with Madeira .
Since the large turtles were particularly in demand, it was mainly the sexually mature females that were important for the population that were caught. The gradual decline in catch quotas during this period is a sure sign that fishing has had a significant negative impact on the development of the diamond turtle population. Studies on other turtle species such as the Macrochelys temmincki also show that due to the low reproductive rate, even low catch quotas lead to significant population losses.
In Chesapeake Bay, licensed fishermen are still allowed to catch turtles for consumption. The annual catch quota is estimated at 10,000 animals. There is a particular demand for turtles as food from ethnic minorities such as the Chinese. The retail price per turtle was around $ 20 in New York markets in the early 2000s.
Loss of stocks due to bycatch in the shrimp fishery
However, where traps are used to fish for blue crabs ( Callinectus sapidus ) on the North American east coast , the bycatch rate of diamond turtles is high. The threat to the population that it poses is much greater than that of the still permitted commercial fishing for diamond turtles. A study now more than 20 years old estimated the daily bycatch by the 743 commercial shrimp fishermen to be 2,500 diamond turtles. As air breathers, the diamond turtles suffocate within a few hours when they fall into these traps. The protective measures introduced therefore include crab traps, which are designed in such a way that turtles cannot get to the bait placed in them.
Stock losses due to road traffic
Road traffic has a major negative impact on the diamond turtle population. Roads that open up the coastal areas for tourism often run through the nesting sites of the diamond turtle. On the way there, especially the sexually mature and egg-bearing females, which are important for the preservation of the population, are regularly run over. In a rather unusual measure to preserve the diamond turtle in New Jersey since 1997, these run-over animals have been dissected by the Wetland Institute in Stone Harbor, New Jersey, and the Richard Stockton College of New Jersey, and the undamaged eggs are removed and artificially hatched.
Artificial rearing as a protective measure
There are several initiatives in the United States aimed at banning the commercial trade in diamond turtles by law. In addition, newly laid nest pits are protected by surrounding them with wire baskets so that predators can no longer dig up the clutches.
Headstarting is another, sometimes controversial, measure to increase inventory numbers. As a rule, eggs are artificially hatched and the young turtles are brought through the first winter at elevated holding temperatures and regular feeding. The winter rest, which otherwise occurs in the wild, is dispensed with. At the end of their first winter, such diamond turtles have reached a size equivalent to that of two to three year old turtles in the wild. If the animals are then abandoned, the likelihood that they will fall victim to predators is much lower.
Artificial rearing is used on a number of turtle species. The method is controversial for a number of reasons. It has not yet been proven that turtles raised in this way adapt to life in the wild. There is also insufficient evidence that these turtles will reproduce once they have reached sexual maturity. In the case of the diamond turtle, most headstarting programs are therefore limited to clutches in which there is little or no likelihood that the eggs they contain will hatch.
Systematics
The diamond turtle is one of the Halsberger turtles , which began to develop during the Jurassic period 180 million years ago and are still represented today with 13 families. The turtles belonging to these groups can retract their heads into the shell. The cervical vertebrae of these animals are specially shaped for this purpose, so that the backbone can curve in an S-shape. The family to which the diamond turtles are assigned is that of the New World pond turtles .
Fossil finds on the coast of South Carolina suggest that the diamond turtle evolved in the Pleistocene . Some details of the skull and tortoise shell show a close relationship to the living only in freshwater Map turtles on. In both species the pterygoid parts of the upper skull lack the lateral appendages to the basioccipital . At the end of the carapace it can be seen that there are furrow impressions of the postcentral shields on the pygal plate.
The diamond turtle either developed from the genus of the mute turtles or both genera are descended from a common ancestor, also bound to freshwater. The evolutionary development of the salt-tolerant diamond turtle from a species living in freshwater may initially have taken place through a behavioral adaptation in which the turtles only consumed saltwater while they were eating. Such behavior can also be found, for example, in the snapping turtles living in fresh water, which can thus survive for a short time in water with a high salt content. This was increasingly followed by a gradual physiological adaptation that led to the development of glands through which salt could be excreted. Through these adaptations, diamond turtles opened up a food-rich habitat that they only had to share with a few competitors.
swell
literature
- D. Alderton: Turtles and Tortoises of the World . New York 1988, ISBN 0-8160-1733-6
- Barbara Brennessel: Diamonds in the Marsh: A Natural History of the Diamondback Terrapin. University Press of New England, 2006, ISBN 1584655364
- CH Ernst, JE Lovich, RW Barbour: Turtles of the United States and Canada . New York 2000, ISBN 1560988231
- Ronald Orenstein: Turtles, Tortoises and Terrapins - Survivors in Armor , Firefly Books Inc, Buffalo 2001, ISBN 1-55209-605-X
- DG Senn: A natural history of the turtles . Bottmingen / Switzerland 1992
- H. Vetter: Turtles of the World - turtles of the world . Frankfurt / M. 2004, Volume 2: North America , ISBN 3-930612-57-7
Individual evidence
- ↑ All dimensions according to nettle, p. 20f
- ↑ Such studies were conducted for Wellfleet Harbor, Cape Cod, Massachusetts and for Kiawah Island, South Carolina. Nettle, p. 54
- ↑ An overview of the morphological differences between the individual subspecies can be found in Nettle, p. 11 and page 22ff
- ↑ In her monograph, the author Barbara Brennessel points out that the colonization of mangroves by diamond turtles is atypical, but in terms of its essential characteristics, the Florida Bay with the Florida Keys that border it resembles that of a spacious estuary. See also nettle, p. 76
- ↑ a b c Orenstein, p. 88
- ↑ DM Whitelwas and RN Zajac: Assessment of prey availability for diamondback terrapins in a Connecticut saltmarsh , Northeastern Naturalist, 2002, Volume 9 (4), pp 407-418
- ^ WM Palmer and CL Cordes: Habitat Suitability Index Models: Diamondback Terrapin (Nesting) - Atlantic Coast. , US Department of the Interior, Fish an dWildlife Service, Research Development, National Wetlands Research Center, Washington, 1988, DC Report 82
- ↑ Barbara Brennessel reports in her monograph on the diamond turtle that earlier commercial collectors of diamond turtles found them, among other things, because of the cracking noise when eating.
- ↑ D. Middaugh: Reproduction ecology and spawning periodicity of the Atlantic silverside Menidia menidia. 1981, Copeia, Vol. 4, pp. 766-776.
- ^ Nettle, p. 38 and p. 39
- ^ Nettle, p. 37f
- ^ WA Dunson: Some aspects of electrolyte and water balance in the estuarine reptiles, the diamandback terrapin, American and "saltwater" crocodiles , Comparative Biochemical Physiologie, 1970, Volume 32, pp. 161-174
- ↑ Nettle, p. 28
- ↑ a b J. Davenport and Ward JF: The effect of salinity and temperature on appetite in the diamandback terrapin terrapin Malaclemys , Herpetological Journal, 1993, Volume 3, pp 95 to 98
- ^ Nettle, p. 29ff
- ↑ Nettle, p. 33f
- ↑ Nettle, p. 36
- ^ Nettle, p. 79ff
- ^ JS Hauswaldt and TC Glenn: Population genetics of the diamondback terrapin (Malaclemys terrapin) , Molecular Ecology, 2005, Volume 14, pp. 723-732
- ^ Nettle, p. 81
- ^ CC Goodwin: Aspects of nesting ecology of the diamondback Terrapin (Malaclemys Terrapin) Rhode Island , Diploma thesis in Zoology, 1994, University of Rhode Island
- ^ Nettle, p. 90ff
- ^ Nettle, pp. 93-96
- ↑ For a more detailed description, see, for example, Orenstein, pp. 194ff
- ↑ Nest temperature and sex of the hatched turtles show no linear relationship. At a nest temperature of 34 degrees, one of the 13 hatched animals was a male. On the other hand, a constant temperature of 30 degrees only resulted in females. S. a. Nettle, p. 97
- ^ S. for example RA Seigel: Growth rates, sex ratio, and population structure of diamand terrapin from the Atlantic Coast of Florida , Proceedings of the 28th Annual Meeting of the Herpetologists' League; 23rd Annual Meeting of the Society for the Study of Amphibians and Reptiles (Abstract), 1980, pp. 87 to 88.Seigel caught ten times more males than females with the same fishing method in winter. In late spring and summer, the gender ratio was five to one.
- ^ Nettle, p. 78
- ↑ Orenstein, p. 198.
- ^ Nettle, p. 125.
- ↑ Nettle, p. 31 f.
- ^ Nettle, p. 41
- ^ Nettle, p. 49, pp. 65 and 66
- ↑ This statement was made, for example, on Kiawah Island, South Carolina. See nettle, p. 65
- ↑ Barbara Brennessel reports, among other things, that people involved in the protection of the diamond turtle occasionally urinate on freshly laid nests in order to protect them from being excavated by raccoons, see also Brennessel, p. 104
- ↑ Nettle, p. 107. Nettle reports that raccoons rummage through places where turtles traditionally lay eggs up to 2 weeks before the start of laying in order to find nests
- ↑ Orenstein, p. 200. Orenstein writes: Turtles have only a small chance of hatching from the egg and an even smaller chance of surviving the first year of life .
- ^ Nettle, p. 57
- ↑ MH Draud, M. Bossert and S. Zimnavoda: Predation on hatchling and juvenile diamondback terrapins (Malaclemys terrapin) by the Norway rat (Rattus norvegicus) , Herpetology, 2004, Volume 38 (3), pp 467-470
- ↑ Raccoons can swim and it cannot be ruled out that they entered the reserve in this way. It is no less likely, however, that the raccoons, which are occasionally kept as pets in the USA, were released on the reservation
- ^ Nettle, p. 59f
- ^ Nettle, p. 137
- ↑ Orenstein, p. 88. Similar phenomena also exist for other foods: The prestige of salmon as a food rose after the stocks in the Central European rivers fell significantly
- ^ Nettle, pp. 138 and 140
- ^ Nettle, p. 143
- ↑ Brenessel, pp. 145 f .; From page 140 onwards, Brenessel also describes a range of preparation methods
- ↑ Orenstein, p. 248
- ↑ Nettle, p. 64
- ^ Nettle, p. 146
- ↑ JM Bishops: Incidental capture of diamondback terrapin by crab pots , Estuaries, 1983, Volume 6, pp. 315-321
- ↑ Occasionally hatched turtles are caught and kept in captivity for the first winter
- ^ Nettle, p. 126
- ↑ In the case of sea turtles, for example, it cannot be ruled out that hiking trails are marked in the first phase of life. This would not be the case for young animals raised in an artificial environment
- ↑ Female turtles usually return to the same clutch racks. It is not sufficiently known when the embossing takes place on these racks. If it occurs immediately after hatching, turtles that have hatched and hatched in an artificial environment may be malformed
- ↑ For a more detailed description of different headstarting programs, see Brennessel, pp. 125–132.
- ^ Fritz Jürgen Obst : Schmuckschildkröten , Ziemsen Verlag, Wittenberg Lutherstadt 1985, ISSN 0138-1423 , p. 31
- ↑ JL Dobie: The taxonomic relationship between Malaclemys Gray 1841 and Graptemys Agassiz 1857, Tulane Stud. Zool. Bot, 1981, Vol. 23, pp. 85-102
- ^ WA Dunson and FJ Mazzotti: Salinity as a limiting factor in the distribution of reptiles in Florida Bay: A theory fort he estuarine origin of marine snakes and turtles , Bull. Mar. Sci, 1989, Vol. 44, pp. 229-244
