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The American Crocodile
(Crocodiles acutus)
Crocodylus acutus, or more commonly referred to as the American crocodile, …is the second most widely distributed of the New World crocodiles, ranging from the southern tip of Florida, both the Atlantic and Pacific Coasts of Southern Mexico, as well as the Caribbean islands of Cuba, Jamaica, and Hispaniola (1 Species). These areas provide the perfect climate for these endangered species that have roamed the earth for over 200 million years. Florida is known for its large population of American alligators, which are often confused for the rare American crocodile. However, there are vast differences between the two species. Hunted for their hides and the changing of their habitat to beach front property is slowly pushing the American crocodile out of Florida, the only place it is found in the United States.
For 190 million years before the first humans evolved, huge populations of crocodilians, in more or less their present form, inhabited the waters and shorelines of rivers, lakes, swamps, and estuaries of tropical and subtropical lands. Today they represent the last true survivors of the huge reptiles that once dominated the seas and landmasses of Earth for over 200 million years (6 Levy). However, …It is inappropriate to treat crocodilians as living fossils whose inferiority forced them into a marginal ecological role as amphibious predators in a world now dominated by mammals. In fact, they are highly specialized for their particular mode of life and have undergone considerable changes during their long evolutionary history… (14 Ross). Among living vertebrates, crocodilians are most closely related to birds rather than to lizards (14). Even though these two groups are now adapted to different modes of life, they both have an elongate outer ear canal, a muscular gizzard, and complete separation of the ventricles of the heart. Crocodilians are the most advanced of all reptiles. They are elongated, armored, and lizard-like, with a muscular, laterally shaped tail used in swimming. The snout is also elongated, with the nostrils set to the end to allow breathing while most of the body remains submerged under water. The success of the Crocodile is evidenced by the relatively few changes that have occurred since crocodilians first appeared about 200 million years ago. The Crocodile belongs to the family Crocodylinae, which consists of those organisms sharing common crocodilian traits. This Family is further divided into three subfamilies: Alligatorinae (alligators), Gavialinae (gharial), and Crocodylinae (crocodiles).
Very often the American alligator (Alligatorinae mississippiensis) is confused for an American crocodile, even though these two species are of the same family they are different in many ways. The alligator has a much broader snout and the crocodile a much narrower snout- …narrower snouts usually indicating fish eating-species. Another characteristic seen in the American crocodile and not the alligator is the front two teeth that penetrate the upper jaw from below as they grow. These teeth are one of the major differences between crocodiles and alligators.
A not so recognizable difference between the American crocodile and alligator is the crocodile's ability to regulate saltwater balance in their body. Crocodiles maintain salt concentrations in their body fluid at the typical level of other vertebrates, which is about one-third that of seawater. The osmoregulatory problems posed by life in fresh or saline waters are related to the amounts of water and salts exchanged across various body surfaces. Loss of salts and water occurs in feces and urine, through respiration, excretion from salt glands in the tongue, and through the skin. The ability of the American crocodile to tolerate salt water is related to their low rate of water loss, low rate of sodium uptake, the ability to excrete excess sodium, and their ability to osmoregulate regularly behaviorally by not drinking saline water or by seeking fresh water after feeding in saline areas. [The American crocodiles will not drink seawater even when they are dehydrated and the American alligator will. However, the alligator does not have the ability to excrete excess sodium].
While the American Crocodile is able to regulate its salinity it is not able to maintain a constant body temperature. Crocodiles, like all reptiles, are cold blooded or pokilothermic. Crocodiles utilize a complex series of physiological and behavioral mechanisms to maintain an even body temperature. When their body temperature drops, they use solar radiation to heat their bodies as they emerge from the water to bask in shallow waters or on the shoreline. As their temperature rises they hold their mouths agape to allow some evaporative cooling. The membranes of the mouth cavity play a major role in regulating temperature. Sometimes crocodiles will partially bask in the sun with their tail or head in the water, this allows them to optimally adjust their temperatures. Body temperature can also be adjusted by shunting blood towards or away from their surface. As crocodiles cool the superficial blood vessels constrict, thereby limiting the amount of heat loss at the animal's surface and maintaining a steady core temperature. [Another temperature-regulating strategy is mud bathing, which provides another layer of insulation against extremes in environmental temperatures].
The American crocodile is found in subtropical to tropical area, were it is optimal for body temperature regulation. It is considered an estuarine species that is capable of migrating through salt water. It is quite the sea going species ranging from Equador along the Pacific Coast to western Mexico, and from eastern Mexico to Guatemala, the coastal areas of Colombia and Venezuela, and north through the Caribbean to the southernmost tip of Florida (40 Guggisberg). This species is the common resident of coastal habitats, large rivers, and lakes within its range (65 Ross). Populations are known from freshwater areas located well inland, including a number of reservoirs (1 Species). In Florida, C. acutus can be found in mangrove swamps and saltwater marshes with sandy, undisturbed high spots (10B Sun-sentinel). South Florida is the northern end of [C. acutus's] range. Historically, crocodiles have lived in Florida from Cape Sable to Lake Worth in Palm Beach County, and fewer numbers, up to Sanibel on the west coast. The largest population in Florida has always lived in the extreme southern end of the peninsula. Because of destruction of habitat, the crocodiles' range is now limited to the undeveloped areas from Cape Sable to North Key Largo and Turkey Point (6H Weinlaub).
The American crocodile was placed on the endangered species list in 1975. [C. acutus} produces a commercially valuable hide and the principal reason for past declines in population size can be attributed to the extensive commercial overexploitation that occurred from the 1930s into the 1960's (1 Species). In most populations C. acutus is extensively hunted with only one or two populations being adequately protected in national parks in Costa Rica, Venezuela, and the United States (226 Ross). Once crocodilian skin was a source of high-quality, pliable, decorative leather that takes on a bright sheen when processed, trafficking in skins became big business with huge returns. Crocodilian skins are processed into a large variety of very expensive leather products. In the early 1900s US tanneries alone were processing between 250,000 and 500,000 skins per year. As supplies dwindled (crocodiles), prices rose and so did the profitability of hunting. Even after protective laws were enacted, the profit incentive encouraged large-scale poaching and smuggling of illegal skins by middlemen servicing the tanneries and leather markets. By the middle of the 1960s crocodile hunting had left many species critically threatened, including the American crocodile near to extinction. Today the world market for crocodilian skins is about 2 million hides per year. Some of these come from licensed, controlled hunting and some are harvested from the captive populations on farms and ranches. These skins are considered to be illegal, but at least a million of the hides taken annually are obtained from poachers. (102 Levy). Also, Habitat destruction is responsible for reduction, and in inhabited area motor vehicles are a major killer of crocodiles.
[The American crocodile almost disappeared from its only habitat in the United States, by the 1970s. But now, A well-protected population of crocodiles exists at the southernmost tip of Florida. The transformed natural landscape that limited their range now supports about 500 animals. Habitats have been protected by both state and federal agencies as well as by the nuclear power industry. The major nuclear power plant of South Florida at Turkey Point has found increasing numbers of the endangered crocodiles in residence and even successfully breeding in the 168 mile network of mangrove-lined cooling canals]
. At first environmentalists challenged the nuclear power plant at Turkey Point, because the heated water, that is a byproduct of the plant, seemed sure to kill seagrasses in Biscayne Bay. The Power company's solution: an extensive network of cooling canals where the water would be cooled before it was returned to Biscayne Bay. As the canals were dug, the extra sand was piled alongside, fashioning a perfect place for a crocodile to nest (1A McClure). [The Florida Power and Light Company has spent hundreds of thousands of dollars in crocodile research efforts and has abandoned plans for expansion of the power plant, leaving the crocodile habitat safe for the foreseeable future] (120 Levy). Once chased by development into a 20-square mile patch of southern Dade County and the northern Florida Keys, crocodiles now are reproducing enough that they are spreading out again. The generally secretive reptiles are showing up along much of South Florida's coast, from Sanibel Island to the Bonnet House in Ft. Lauderdale. [It is the explosion of suitable nesting sites that is driving the crocodile's recovery, which saw an estimated 20 nests in 1974 climb to at least 42 in 1995] (1A). Nesting is the most reliable way to tell if crocodiles are re-colonizing an area, so a clutch of eggs discovered on Sanibel Island [in 1995] was particularly encouraging for researchers, even though none of the eggs were hatched (1A). In [1993] there was a record year at Turkey Point, with 12 nests and 155 hatchlings found. And, in [1994] nine nests and 153 hatchlings were recorded a month into hatching time.
The crocodiles lay their eggs on land in exposed sites, usually within 30 feet of the water… Mound nests are composed of sand and earth combined with a great deal of plant material (grasses, water reeds, and leaves), the decay of which releases heat to help insulate the eggs. The hole is excavated with the hind feet, and the excavated soil is subfrequently used to cover the eggs. Mostly as a mound-nesting species the crocodile will first gather a collection of leaves, grasses, reeds and other plant litter at the selected nesting site and then create a mound using this plant material combined with earth or sand. Then the mother compacts all the material into a firm, solid mound. Finally, she excavates a cavity up to two feet deep, lays her eggs and covers them up.
In crocodilians, the temperature experienced by the embryo in its egg is a major determination of hatchling sex, this is referred to as temperature-dependent sex determination or TSD. TSD has been proven in five species of crocodiles and is probably true for all species, because crocodilians lack sex chromosomes. Exclusively females are produced at low incubation temperatures, males are produced at intermediate temperatures, and high temperatures produce mostly or only females. Where the female builds her nest and when she lays her eggs both have major effects on the sex ratio for her offspring. Thermal cues probably play a major role in nest-site selection and construction. It is not surprising that, in many crocodilian nests, all of the siblings are of the same sex. The crucial period of thermal sensitivity begins early in development and extends throughout the first half of incubation (120 Ross). Without knowing it FPL created ideal nesting sites for crocodiles (1E Miller). Along with the cooling canals of Turkey Point, Everglades National Park, and Key Largo are the key breeding areas for C. acutus.
As American crocodiles produce commercially valuable hide, sustainable utilization programs based on ranching and farming are feasible, However, the development of management programs based on sustainable utilization must be approached on a country-by-country basis and be directly linked to the health of wild populations. A majority of countries [8 of the 17] that the crocodile inhibits have management programs based on complete protection, but only a few have enforced legislation. El Salvador and Haiti have no management programs whatsoever. In five countries, farming of the American crocodile has begun (3 Species).
In the early 1960s, the wild crocodilian resource necessary for the skin trade had dwindled and the first conservation laws were enacted, resulting in a simultaneous rise in prices and in the demand for skins. It was at this time that farsighted conservationists and skin producers started to investigate the feasibility of farming and ranching crocodilians on a sustained, commercial basis. Conservation and educational farms aim at breeding endangered species, such as the American crocodile, in captivity for possible release back into protected areas in the wild. Commercial development and international trade in endangered species such as crocodiles must satisfy the criteria of the convention on International Trade in Endangered Species of Fauna and Flora (CITES). Commercial farms must be able to demonstrate, for a defined geographic area, that the impact of harvesting is not detrimental to the survival of the species.
Current efforts are being made to preserve the habitat of the American crocodile (Crocodylus acutus), whose relatives date back as far as 200 million years. The American crocodile, …is the second most widely distributed of the New World crocodiles, ranging from the southern tip of Florida, both the Atlantic and Pacific Coasts of Southern Mexico, as well as the Caribbean islands of Cuba, Jamaica, and Hispaniola (1 Species). The American crocodile is often confused for its cousin the American alligator the more aggressive and dominant reptile of Florida. However, there are vast differences between the two species. Hunted for their hides and the changing of their habitat to beach front property is slowly pushing the American crocodile out of Florida, the only place it is found in the United States. Perhaps with the continued efforts of FPL and CITES the American crocodile will become a more abundant species.
Bibliography
Internet
World Book
Word Count: 2378
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