Vermont Herpetology - Endangered Reptiles and Amphibians of the World - II.
Vermont HerpetologyVermont Herpetology
Endangered Reptiles and Amphibians of the World - II. The Black Caiman, Melanosuchus niger.
Introduction

Whilst Africa, Asia, and Australia are the stronghold of the crocodiles, the Americas is truly where the family Alligatoridae (containing the alligators and caimans) rule. Of the 8 different species of Alligator, only one, the Chinese alligator (Alligator sinensis), is found outside of North, Central, and South America. The Alligators that comprise the American contingent include the American alligator (A. mississippiensis), the widespread Spectacled caiman (Caiman crocodilus), the Broad-snouted caiman (C. latirostris), and the adaptable Yacaré caiman (C. yacare). Two dwarf species of caiman are found only in South America, Cuvier's Dwarf caiman (Paleosuchus palpebrosus) and Schneider's Dwarf caiman (P. trigonatus). The final species of Alligator found in the Americas, and the subject of this article, is the sole member of the genus Melanosuchus, the Black caiman (M. niger).

The Black caiman represents the largest species in the family Alligatoridae, slightly surpassing in size the American alligator. Male Black caiman commonly grow to 4 meters in length and on very rare occasions can reach up to 6 meters. Large Black caiman are noticeably more robust than other crocodilians of this length. For instance, a skull procured from a Venezuelan 3.9 metre Black caiman was found to be longer and heavier than a skull from a 4.8 metre Nile crocodile (Crocodylus niloticus; Ross, pers. comm.). Females remain smaller, usually attaining a size slightly under 3 meters in length. The Black caiman is known by various common names, including the Jacaré assu (as well as açu, uassu, and guaçu), Jacaré negro, Caimán negro, and Cocodrilo. As many of these names suggest, Black caiman are dark dorsally in coloration but possess a light cream underside. The lower jaw and flanks of the animal contain lighter banding patterns. Compared to other caiman, M. niger possesses large eyes and a narrow snout. Typical of other caiman, nevertheless, is the bony ridge that travels between the orbits of the eyes and continues down the snout.

Natural History

The range of Black caiman, historically, covered a vast area of the Amazon basin in South America, northwards into Ecuador, Colombia, French Guiana, Guyana, and extending southwards though the Amazon Basin in Brazil, down to Bolivia and Peru (figure 1). Although this species of caiman is sympatric with other alligators, crossbreeding between species does not seem to occur. It has been suggested that this may be a consequence of occupying different environmental niches (Herron 1994). The animals are never found far from a source of freshwater, and, as such, their typical habitat consists of rivers, lakes, quiet backwaters, and at certain times of the year, flooded forests and open plains.

Black caiman distribution
Figure 1. Distribution of Black caiman in South America (source: Ross 1998).
Despite their largely aquatic tendencies, Black caiman prey significantly on terrestrial mammals, an occurrence owed in part to their highly developed sense of vision and hearing. Rodents form a substantial part of their diet, and the largest species of rodent, the Capybara (Hydrochaeris hydrochaeris), is a particularly popular prey item amongst larger caiman. Other preys taken include otters, small deer, other caiman, and occasionally fish such as piranha and catfish. Attacks on domestic animals, such as dogs and cattle, and, on occasion, humans, have also been reported. Juvenile caiman feed more commonly on small fish, snails, amphibians, insects, and crustaceans of appropriate size.

Declining populations of Black caiman have apparently resulted in gross ecological changes over much of their range. Lack of predation on capybara has seen an explosion in the number of these herbivorous rodents, and a corresponding destruction of vegetation and crops. In addition, a reduced level of caiman excrement, a basic component at the bottom of the food chain, has reportedly lowered the abundance of various microorganisms, including invertebrate larvae and plankton. In turn, this has reduced population numbers of fish fry that utilize microorganisms as a food source.

Captive Care

As with all crocodilians, with the possible exception of the Dwarf caimans, maintenance in captivity is beyond the reach of private reptile keepers. Several zoos, however, do maintain limited numbers of Melanosuchus.

Reproduction

Melanosuchus breed during the dry season, upon at which time males and females congregate. Adult males exhibit antagonistic behavior towards each other at this time in the form of posturing and bellowing. Female Black caiman construct a mound in which to nest, measuring around 1.5 metres in diameter and up to 0.75 metres in height. Into the nest are deposited between 30 and 65 large eggs averaging 140 grams each in weight. Following oviposition, the eggs are generally guarded by female caiman until hatching, which usually occurs 35-45 days later, although sometimes longer depending on the ambient temperature. Frequently, females will nest in close proximity, presumably to deter predators and result in safety in numbers once the babies hatch. Fully developed caiman, with the aid of their mother, emerge from their eggs and soon thereafter, start to look for their first shelter and meal.

Endangered Status

The distribution of the Black caiman was once vast, however, the same cannot be said about populations of these animals today due to over-zealous hunting practices (Smith 1980). M. niger have been completely exterminated in many areas where they were once common, and significant populations remain only in very remote areas. It has been estimated that Black caiman have been reduced in numbers by 99 % throughout the last hundred years.

Substantial hunting of Melanosuchus began during the middle of the twentieth century, following severe depletion of Crocodylus acutus and Crocodylus intermedius stocks. These two species were more prized in the leather industry due to their larger, higher grade skins. Skins were largely exported to North American and European tanners, and used in the manufacture of miscellaneous luxury items such as wallets and shoes. Intense hunting continued for over a decade. Between the years 1950 and 1965, an estimated 7.5 million caiman skins were exported from the state of Amazonas alone, the majority of which were most likely Black caiman (Smith 1980). Hunting continued up to the early 1980's, by which time only approximately 10 % of exported skins were from Melanosuchus. As the markets for Black caiman hide diminished due to national and international legislature, in addition to changes in public opinions, hunters began profiting from the sales of salted caiman meat (Da Silveira and Thorbjarnarson, 1999). To this day, the meat is either used as bait for fishing or mixed with fish and sold for human consumption. Despite the illegality of the hunt, an estimated 115 metric tons of caiman meat is harvested annually in Western Amazonia alone, comprising over 5,000 Black Caiman and almost 3,000 Spectacled Caiman (Da Silveira and Thorbjarnarson, 1999). To a lesser degree, various other body parts of caiman are utilized for medicinal purposes.

M. niger is listed in Appendix I of the Convention on International Trade in Endangered Species of Flora and Fauna (CITES; Appendix II in Ecuador) and classified by the World Conservation Union (IUCN) as an endangered species. Most recently available data suggests that populations of Black caiman have recovered in several areas of the Amazon. This recovery has progressed to the extent that the animals are increasingly threatening local people, and potential commercial use of the animals hide is being developed. Nevertheless, illegal hunting for their skin continues, which is shrouded by the fact that Black caiman leather is difficult to distinguish from that of the Spectacled caiman. Irrespective of continued hunting, Black caiman face competition from the wide-ranging and more fecund Spectacled caiman. Additionally, habitat destruction continues to add pressure on existing populations.

In summary, Melanosuchus are severely depleted in numbers in the seven nations where they once roamed, with the possible exception of Ecuador. Whilst protected, Black caiman continue to be hunted illegally for their meat, medicinal properties, and hide, although certain local populations are starting to show slight signs of recovery. The vast range over which the animals live and the inaccessibility to their typical habitat makes accurate population studies difficult. Furthermore, this renders the implementation of laws designed to protect the animals a near impossible task. Certain nations, such as Ecuador, have instigated captive farming of Black caiman in the hope of establishing a successful re-introduction program. These types of programs, as well as more effective measures to control the illegal hunting of wild caiman, are required to protect the future survival of this majestic species.

Further Reading

For those with Internet access, a great deal of information regarding all species of crocodilians in addition to further citations can be found at http://crocodilian.com/ and http://www.flmnh.ufl.edu/natsci/herpetology/crocs.htm hosted by the Crocodile Specialist Group. Additionally, the Crocodile Specialist Group has set-up a fund to help conserve the Chinese alligator, details of which can be found at http://www.flmnh.ufl.edu/alligatorfund/, or by writing to Dr. J. P. Ross, Executive Officer CSG, Florida Museum of Natural History, Gainesville, FL 32611, USA, Fax +1 352 392 9367. Further conservation information can be sought in 'Crocodiles : An Action Plan for Their Conservation' by James P. Ross (IUCN, 1998). A comprehensive guide that covers all 23 species of crocodilian is 'Alligators and Crocodiles' by Charles A. Ross and Stephen Garnett (Facts on File, Inc., 1989).

Bibliography

Brazaitis, P., Watanabe, M.E., Amato, G. (1998) The caiman trade. Scientific American, 278, 70-76.

Da-Silveira, R. and Thorbjarnarson, J. B. (1999) Conservation implications of commercial hunting of black and spectacled caiman in the Mamiraua Sustainable Development Reserve, Brazil. Biological Conservation, 88, 103-109.

Herron, J.C. (1994) Body size, spatial distribution, and microhabitat use in the caimans, Melanosuchus niger and Caiman crocodilus, in a Peruvian lake. Journal of Herpetology, 28, 508-513.

Ross, J.P. (ed.). Crocodiles. Status Survey and Conservation Action Plan [Online]. IUCN/SSC Crocodile Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK, 2nd Edition, 1998, viii + 167 pp. Available: http://www.flmnh.ufl.edu/natsci/herpetology/act-plan/plan1998a.htm.

Smith, N.J.H. (1981) Caimans, capybaras, otters, manatees, and man in Amazonia. Biological Conservation, 19, 177-187.


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