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Crocodylus acutus

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Crocodylus acutus

The American crocodile (Crocodylus acutus) is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas. Populations occur from the Atlantic and Pacific coasts of southern Mexico to South America as far as Peru and Venezuela. It also lives within many of the Caribbean islands such as Cuba, Jamaica, Hispaniola, Grand Cayman, Greater Antilles and the West Indies. Within the United States, the American crocodile's distribution is limited to the southern half of Florida - though at least two have been found as far north as the Tampa Bay area -[1] and has an estimated population of 2,000; a significant comeback from the few hundred crocodiles found back in the 1970s. The habitat of the American crocodile consists largely of coastal areas.[2] It is also found in river systems but has a tendency to prefer some level of salinity, not just tolerance, resulting in the species congregating in brackish lakes, coastal swamps, lagoons, even cays and small islands. Other crocodiles also have tolerance to salt water due to salt glands underneath the tongue, but the American crocodile is the only species other than the saltwater crocodile to commonly live and thrive in saltwater. They can be found on beaches and island formations without any freshwater source, such as some of the many cays and islets across the Bahamas and the Caribbean. They are also found in hypersaline lakes, such as the Lago Enriquillo; one of the largest population known to exist.[3]

The American crocodile is one of the larger crocodile species. This species has a more V-shaped snout compared to other large crocodiles that usually have a slightly wider snout. As a larger species of crocodile, some males can reach lengths of 6.1 m (20 ft), weighing more than 907 kg (2,000 lb).[3] On average, mature males are more in the range of 4.1 m (13 ft) to 4.8 m (16 ft) in length weighing about 400 kg (880 lb).[4] Like other species, females are smaller; rarely exceeding 3.8 m (12 ft) in length.[5] Adults have a uniform grayish-green coloration with white or yellow undersides, while young have dark cross-banding on the tail and back. Despite their large size, American crocodiles do not regularly attack large animals as most large crocodilians do. Fish, reptiles, birds and small mammals make up majority of their diet. On occasion large mammals such as deer and domestic animals are taken. Their dietary habits in coastal regions are not well studied. Like any other large crocodilian, the American crocodile is potentially dangerous to humans, but it is not a very aggressive species and attacks are rare.[6]

Taxonomy and etymology

Cuvier originally described the species as Crocodylus acutus in 1807.[7] Over time, it commonly became known as the "sharp-snout alligator". In 1822, Constantine Samuel Rafinesque postulated the species was in fact a crocodile.[8]

The species was redescribed as Crocodylus floridanus by William T. Hornaday in 1875,[9][10] when Hornaday and C.E. Jackson were sent from Washington, DC to Florida to collect alligator hides. Upon hearing of a "big old gator" in Arch Creek at the head of Biscayne Bay, Hornaday and his companions searched for it and reported:
"In a few hours we got sight of him, out on the bank in a saw-grass wallow. He was a monster for size–a perfect whale of a saurian, gray in color—and by all the powers, he was a genuine crocodile!"[11]

Crocodylus floridanus is now considered an invalid junior synonym of C. acutus.[12][13]

Characteristics

Like all crocodilians, the American crocodile is a quadruped, with four short, splayed legs, a long, powerful tail and a scaly hide with rows of ossified scutes running down its back and tail.[14] Its snout is elongated and includes a strong pair of jaws. Its eyes have nictitating membranes for protection along with lachrymal glands, which produce tears.

The nostrils, eyes, and ears are situated on the top of its head, so the rest of the body can be concealed underwater for surprise attacks.[14] Camouflage also helps it prey on food. The snout is relatively longer and narrower than that of the American alligator, although broader on average than that of the Orinoco crocodile. American crocodiles are also paler and more grayish than the relatively dark-hued alligator. This crocodile species normally crawls on its belly, but it can also "high walk".[15] Larger specimens can charge up to 10 mph (16 km/h).[16] They can swim at as much as 20 mph (32 km/h) by moving their bodies and tails in a sinuous fashion, but they cannot sustain this speed.[17]

The American crocodile is sometimes confused with the smaller, Central American Morelet's crocodile, a smaller species that is native to Mexico.

Size

Newborn hatchlings are about 22 cm (8.7 in) in length and about 60 g (2 oz) in mass.[18][19] The average adult is 4.3 m (14 ft) long and weighs 382 kg (842 lb) in males, and 3 m (9.8 ft) and 173 kg (381 lb) in females.[20][21]

In the Tárcoles River in Costa Rica, dozens of four-meter and a few five-meter individuals frequent bridge crossings (where they are fed daily, which may have helped them reach such consistently large sizes) and are a popular tourist attraction. In their Florida range, adult length has been recorded as high as 5.2 m (17 ft), but adult males on average measure 4.3 m (14 ft) long. This species is said to grow largest in the South American river basins, but even old males rarely reach 6 m (20 ft).[22][23] A skull of this species was found to measure 72.6 cm (28.6 in) and is estimated to have belonged to a crocodile of 6.6 m (22 ft) in length.[24] Large, mature males regularly weigh about 400–500 kg (880-1100 lb), with the individuals of six or more meters surpassing 1000 kg (2,200 lb).[25] Two biologists working with the History Channel series MonsterQuest spotted and filmed a crocodile they estimated to be 16–18 ft, deep within Everglades National Park in Florida.

Distribution and habitat

C. acutus is the most widespread of the four extant species of crocodiles from the Americas.[26] It inhabits waters such as mangrove swamps, river mouths, fresh waters, and salt lakes, and can even be found at sea (hence its wide distribution on the Caribbean Islands,[14] southern Florida, the Greater Antilles and southern Mexico to Colombia and Ecuador.[18][27] The American crocodile is especially plentiful in Costa Rica.[28] One of its largest documented populations is in Lago Enriquillo, a hypersaline lake in the Dominican Republic.[21] The species has also been recorded from Jamaica.[29]
American crocodiles have recently been sighted in Grand Cayman, leading experts to believe the species may be swimming from Cuba (which is home to a massive American crocodile population) and slowly repopulating Grand Cayman. In addition, an American crocodile/Cuban crocodile hybrid was recently discovered in the Cancun area. The crocodile likely originated in the Zapata Swamp of Cuba (the only place where these wild hybrids exist) and swam to the Yucatán Peninsula. Their saline tolerance also allowed the American crocodile to colonize limited portions of the United States (only extreme southern Florida.) Contrary to popular misinformation, the presence of the American alligator is not the reason the American crocodile was unable to populate brackish waters north of Florida, but rather the climate.


American crocodiles, unlike American alligators, are extremely susceptible to cold temperatures and live exclusively within tropical waters. During 2009, unusually cold weather in southern Florida resulted in the deaths of about 150 wild American crocodiles, including a well-known crocodile which inhabited Sanibel Island far north of their natural range.[30][31]

American crocodiles in the United States coexist with the American alligator, and are primarily found in Everglades National Park, Florida Bay, Biscayne Bay and the Florida Keys from Miami southward.[19][32] A sizable population occurs near Homestead, Florida, at the Turkey Point Nuclear Generating Station.[19][33][34] Some individuals wander northward to warm summer waters and have been sighted in Sarasota County and Palm Beach County.[18] In the summer of 2008, a crocodile was captured in the surf on Isle of Palms, South Carolina. In 2013, a 700 pound crocodile was captured in Tarpon Springs, Florida.[35]

Crocodiles require consistent tropical temperatures, hence their lack of distribution within the southern United States. They are saltwater-tolerant and have thus been capable of colonizing a multitude of islands within the Caribbean and on some coastal pacific islands as well. They coexist with the very small spectacled caiman within Central America. The only other crocodiles present within the American crocodile's range are the smaller and critically endangered Cuban crocodile, along with the small Morelet's crocodile in southern Mexico and Guatemala.

Biology and behavior

American crocodiles are more susceptible to cold than American alligators.[32] While an American alligator can survive in water of 7.2 °C (45.0 °F) for some time, an American crocodile in that environment would become helpless and drown.[14] American crocodiles, however, have a faster growth rate than alligators, and are much more tolerant of salt water.[14]

Cleaning symbiosis involving the American crocodile as client has been described. Unlike the Old World crocodiles which are sometimes cleared of parasites by birds, the American crocodile relies more on fish for parasite removal.[14]

Hunting and diet

American crocodiles' primary prey throughout life is fish; the relatively narrow snout is indicative of this piscivorous preference. Virtually any fish found in freshwater through coastal saltwater habitats is potential prey. In Florida, bass, tarpon and especially mullet appeared to be the primary prey.[36] The snout of the American crocodile is broader than some specialized fish-eating crocodilians (i.e. gharials, freshwater crocodile, etc.), allowing it to supplement its diet with a wider variety of prey. Prey species have ranged in size from the insects taken by young crocodiles to full-grown cattle taken by large adults, and can include various birds, mammals, turtles, crabs, snails, frogs, and occasionally carrion.[21][27] Adult American crocodiles have no natural predators and almost any terrestrial or riparian animal they encounter is potential prey. Reportedly, these crocodiles hunt primarily in the first few hours after nightfall, especially on moonless nights, although they will feed at any time.[36]

Reproduction

American crocodiles breed in late fall or early winter, engaging in drawn-out mating ceremonies in which males emit very low frequency bellows to attract females. Body size is more important than age in determining reproductive capabilities, and females reach sexual maturity at a length of about 2.8 m (9.2 ft). In February or March, gravid females will begin to create nests of sand, mud, and dead vegetation along the water's edge. Nest location is crucial, and with the correct amount of vegetation, the eggs will develop within a small temperature range. Because sex determination is temperature-dependent in crocodilians, slight aberrations in temperature may result in all-male or all-female clutches, which would possibly harm the health of the population. About one month later, when it is time to lay, the female will dig a wide hole diagonally into the side of the nest and lay 30 to 70 eggs in it, depending on her size. After laying, the female may cover the eggs with debris or leave them uncovered. The white, enlongated eggs are about 8 cm (3.1 in) long and 5 cm (2.0 in) wide and have a number of pores in the brittle shell. During the 75- to 80-day incubation period, the parents will guard the nest, often inhabiting a hole in the bank nearby. Females especially have been known to guard their nests with ferocity. But in spite of these precautions, crocodile eggs sometimes fall prey to raccoons, foxes, skunks or other scavenging mammals. Crocodilian eggs are somewhat brittle, but softer than bird eggs. Young of this species hatch after 75–80 days.


This species exists mostly in tropical areas with distinct rainy seasons, and the young hatch near the time of the first rains of the summer (July–August), after the preceding dry season and before the bodies of water where they live flood. In this stage of development of their young, mother crocodiles exhibit a unique mode of parental care. During the hatching process, when the young crocodiles are most vulnerable to predation, they will instinctively call out in soft, grunt-like croaks. These sounds trigger the female to attend to the nest, uncovering the eggs if they have been covered. Then she will aid the hatchlings in escaping their eggs and scoop them up with her mouth, carrying them to the closest water source.

The hatchlings, which are 24 to 27 cm (9.4 to 10.6 in) in length, have been reported to actively hunt prey within a few days of hatching. It is not uncommon for the mother to care for her young even weeks after they have hatched, remaining attentive to their calls and continuing to provide transportation. About five weeks after hatching, the young crocodiles disband in search of their own independent lives. Most of them, of course, will not survive, being preyed upon by various raptorial birds and larger fishes. Those that do survive the early stages of life will grow rapidly, feeding on insects, fish and frogs. Additionally, some young crocodiles reportedly will feed on each other.[36]

Conservation status

Due to hide hunting, pollution, loss of habitat, and removal of adults for commercial farming, the American crocodile is endangered in parts of its range.[19] In 1972, Venezuela banned commercial crocodile skin harvesting for a decade, as a result of 1950s and 1960s overhunting.[37]

One thousand to two thousand American crocodiles live in Mexico and Central and South America, but populations are data deficient.[21] The American crocodile is considered a vulnerable species, but has not been assessed since 1996.[26] It has an estimated wild population of 500 to 1,200 in southern Florida.[38] On March 20, 2007, the United States Fish and Wildlife Service declassified the American crocodile as an endangered species, downgrading its status to "threatened"; the reptile remains protected from illegal harassing, poaching or killing under the federal Endangered Species Act.[39][40]

Relationship with humans

American crocodiles are dangerous to humans; attacks in Mexico, Costa Rica, and Panama are not unprecedented. These attacks rarely make international news, so this species is not as well-documented as a man-eater, as are its relatives.[14] The species is often reportedly timid, and seemingly lacks the propensity to attack people as regularly as Old World crocodiles do.[8] However, it is more likely than the American alligator to be aggressive towards humans.[36] In May 2007, two instances occurred within one week of children being attacked and killed by this species—one in Mexico just south of Puerto Vallarta and one in Costa Rica.[41][42]

See also

References

External links

  • American Crocodile
  • American Crocodile at Crocodilian Species List
  • University of Florida's crocodile research in Southwest Florida
  • National Parks Conservation Association - American Crocodile

Media

  • Crocodylus acutus at CalPhotos
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