Black Caiman

[Dark Jaguar]

Jacaré Açu (Melanosuchus niger)

I've been working alot on creating this thread for months already that will be All About Black Caimans including sizes, studies, accounts, videos, pictures, behavior, conflicts with humans, intra/inter specific interactions and more. It'll be all about this very underrated Reptile Species and its more than about time to show more of them to the world as they're also one of the very Top predators of Brazil and South America.

I will share all about the Jacaré Açu here and Feel free to share anything related to this specific Species and the other Caimans species in the already existing Caiman thread.

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BLACK CAIMAN ( JACARÉ AÇU )

From the study: DYNAMICS AND POPULATIONAL STRUCTURE OF JACARÉ-AÇU (Melanosuchus niger) IN AMAZÔNIA.

https://pdfs.semanticscholar.org/3faf/7b...8e71e4.pdf

Natural history of Melanosuchus niger.

Etymologically, the name Melanosuchus nigerderiva from the Greek "melanos" (black), "souchus" (crocodile) and "niger" (black), given predominant accordion of this species (Vasquez, 1991). In Brazil, it is popularly known as Jacaré-Açu, a word that comes from the tupi guarani and means large caiman or larger caiman.

Melanosuchus niger is one of the 23 species of the order Crocodylia. Black Caiman is considered the largest predator of the Amazon basin. Males reach an Average of 4 meters of total length (Vasquez, 1991), although there are records of specimens measuring up to 6 meters long (Medem, 1983; Plotkinet al., 1983). Females reach sexual maturity at 2 meters in total length and their average size when adult is 2.8 m. The generation time, that is, the time in which individuals reach sexual maturity is from 10 to 15 years. The nests are made of leaves, branches and twigs in hillocks, where they are placed between 35-50 eggs. The nestlings measure approximately 30 cm in length when they are born and receive their mother's care for a while (Thorbjarnarson, 1996).

Figure 1. Stages of Melanosuchus niger's life cycle (egg, calf, adult).  

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

Cubs/Calves measure approximately 30 cm in length when they are born and receive their mother's care for a while (Thorbjarnarson, 1996).

The black caiman has a wide, smooth snout and a bony prominence that extends from above the eyes down.  Its dorsal coloration is predominantly black when adult, it has 3 to 5 round and black spots on the sides of the jaws and the belly is totally white or yellowish.  The iris is yellowish green. cubs and juveniles are black with yellowish stripes on the body (Rueda-Almonacidet al., 2007).

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GEOGRAPHIC DISTRIBUTION

It is distributed throughout the whole Amazon and they can be found in the rivers of the Amazon basin and those that drain to the Atlantic coast.
It is also found in the backwaters of rivers and mainly in lakes and wetlands.

There is register of the species in Bolivia, Brazil, Colombia, Ecuador, Guyana, French Guiana and Peru (Plotkinet al., 1983). In Brazil, it is distributed in the states of Acre, Amapá, Amazonas, Mato Grosso, Pará, Rondônia, Roraima and Tocantins (Medem, 1983; Plotkinet al., 1983; Ross, 1998). Vasquez (1991) describes the occurrence of black caimans in the rivers Juruá, Purus, Madeira, Tapajós, Xingu, Araguaia, Tocantins, Negro, Trombetas and Amazonas including the islands near the mouth of the Amazon River.  It is most frequently found in waters with little current so it can be observed in river remnants and especially in lakes, flooded woods and shallow marshy areas (Medem, 1963).

Map Figure 2. Distribution of the species Melanosuchus niger. Source: (Thorbjarnarson, 2010).

*This image is copyright of its original author

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CONSERVATION AND STATUS OF BLACK CAIMAN

https://pdfs.semanticscholar.org/3faf/7b...8e71e4.pdf

https://www.iucncsg.org/365_docs/attachm...b37cab.pdf

This species was very abundant in the Amazon. Bates (1863; in (Plotkinet al., 1983)) was impressed by its high densities in the Solimões River.  But during the last century its populations were reduced and some extinct in its natural range. Today it is unusual to see the black caiman in the main channel of the Solimões River (Plotkinet al., 1983).  The main cause of its decline was the commercial interest to obtain leather suffering overexploitation given the superior quality of its leather (Plotkinet al., 1983; Brazaitiset al., 1996; Thorbjarnarson, 1998; Da Silveira and Thorbjarnarson, 1999; De Thoisyet al., 2006). The Black Caiman was the preferred Amazonian species due Melanosuchus niger to its larger size and the superior quality of its skin.

The commercial hunting of M. niger began in the 1930s but reached its peak in the 1950s when approximately 1,200,000 specimens were hunted per year (Ojasti, 1996). Between 1950 and 1965 more than 7.5 million Black Caiman's hides were exported from the state of Amazonas - Brazil alone (Da Silveira and Thorbjarnarson, 1999).

The great demand for skins in Europe and in the United States together and subsequently used  to manufacture  luxury  items  including  belts, wallets and shoes.  With the loss of habitat affected natural populations to the limit of extinction between 1960 and 1969 reaching a high level of fragmentation (CSG, 1995; Britton, 2012). Only after Law No. 5,197 of 1967 the wildlife in Brazil was officially protected but the illegal hunting of Black Caimans continued until 1980 (Plotkinet al., 1983).

In many parts of the species’ range a period of  recovery  likely  began  with  the  demise  of  commercial skin hunting. In the 1970's a major shift in caiman hunting occurred in the western Brazilian Amazon (Amazonas State) with hunters selling caiman meat instead of skins. By the early 1980's a trade in salted meat from Amazonas State to Pará State in Brazil and to Colombia was reported by Best (1984). In the mid-1990's an estimated trade in excess of 100 tons of caiman meat per year was coming from the region of the Mamirauá Reserve (Da Silveira and Thorbjarnarson 1999). The trade has flourished and expanded in various areas as described in the Brazil and Peru country accounts. The biggest conservation challenge  for  the  species  now  is  not  one  of fostering population recovery but rather developing science-based management programs that foster the sustainable use of caiman skins and meat and provide economic benefits for communities that share Amazon riparian habitats with both Black and Spectacled Caimans.

Recent surveys have been conducted throughout most of the range of the M. niger (see country accounts), including some areas where spotlight counts and nest monitoring are being done as part of plans for sustainable harvest programs. (Ortiz van Halle 1995; Alvarez 1995)

The species has recovered substantially in Brazil due to strategies for the conservation and use of caimans that included research on biology, genetics, population density and size structure, habitat selection, movement patterns, ecology, feeding and reproduction, which generated appropriate recommendations for management (Da Silveira and Thorbjarnarson, 1999).

But the natural populations of this species continue to be affected by anthropic actions such as dam construction, deforestation and hunting. The increase in the construction of hydroelectric plants (HPPs) may have an effect on the conservation status of the caiman due to the environmental and ecological impacts they generate in the regions where they are installed (Marioniet al., 2013). The fragmentation of rivers and therefore the loss of connectivity is one of the greatest impacts; the power plants may also cause the flooding of forest areas for the creation of reservoirs as well as deforestation due to road construction (Finer and Jenkins, 2012).

In addition, the use of Black Caiman's, Spectacled Caiman's and River Dolphin's meat as bait to capture Piracatinga (Calophysus macropterus) is a new form of fishing developed in the Amazon. Although this activity possibly began in the 1990s, it was first reported in 2000 when it drew attention to ecological problems due to the impact on populations of caimans and river dolphins (Estupiñánet al., 2003; Brumet al., 2015). It is estimated that in 2013 alone, some 2,300 caimans were killed in the Solimões and Japurá rivers. Recently the Brazilian government created a regulation banning Piracatinga hake for five years, which came into force in January 2015 (Botero-Ariaset al., 2014).

The State of Amazonas is the largest producer of salted and dried caiman meat. Between 1980 and 1999, it is estimated that 65 tons of meat were extracted per year from the Mamirauá Sustainable Development Reserve. In 2005, approximately 50 tons (5000 individuals) were extracted from the Piagaçu-Purus Sustainable Development Reserve (Marioniet al., 2013).

In Brazil as in other Amazonian nations the Black caiman was intensively hunted for its skin in the 20th century. Skin hunting was particularly intense in the early 1950s, and between 1950 and 1965 a total of 7.5 million caiman skins were exported from Amazonas State alone (Carvalho 1967). Commercial hunting of all wildlife, including caiman, was banned in 1967 (Federal Law 5.197), but reports suggest that some illegal skin hunting continued into the l970s and l980s (Medem 1983). By the late 1960s the caiman skin trade had shifted almost entirely to the less commercially valuable C. crocodilus,  indicating  that  hunters  were  finding  it  diffi cult to locate M. niger. In the late 1970s and early 1980s, the scarcity of Black caiman was evident in the fact that only approximately 10% of the confiscated caiman skins in Brazil were of M. niger (Rebelo and Magnusson 1983).

While Black caiman were near commercial extinction, breeding populations of wary animals remained in isolated fl oodplain  habitats  throughout  their  historic  distribution. While some reports in the 1980s suggested that Black caiman was a highly threatened species (Plotkin et al. 1983; Brazaitis et al. 1992), this was due in large part to the inaccessible nature of the areas where the breeding populations remained, and  the  wary  nature  of  the  surviving  animals. In areas of prime habitat in the western Brazilian Amazon, the species recovered relatively quickly following the end of widespread commercial skin hunting, and by the early 1980s there was an emerging industry of hunting caiman for their meat (Best 1984). As populations of caiman grew so did meat hunting until by the 1990s in some areas (such as the Mamirauá SDR region)  there  was  a  large  network  of  hunters  and  traders dealing  in  caiman  meat  (Da  Silveira  and  Thorbjarnarson 1999).

Today, M. niger is common throughout much of the Brazilian Amazon, and there are no reports of populations being locally endangered in the last 15-20 years. In 2007, the population was transferred to CITES Appendix II (Brazil 2007), a move that will facilitate managed commercial use (Dacey 2007). Nevertheless, the abundance of Black caiman is not uniform throughout  the  Amazon  Basin.  The highest  densities  and largest populations occur in the nutrient-rich varzea habitat located along white water river systems with Andean origins, including the Solimoes, Juruá, Japura and Purus. Aside from the sediment-rich white water rivers, Amazonian rivers are classifi ed as blackwater, such as the Rio Negro, or clearwater river systems, such as the Tapajos. These river systems tend to have lower levels of productivity and lack the productive varzea forest floodplains whose lakes are favored by Black caiman. While these types of river systems and their associated wetlands are also inhabited by Black caiman, the latter are typically found at much lower densities (Da Silveira 2002).

In most of the habitats used by M. niger, their abundance is poorly represented by spotlight counts because the species prefers heavily vegetated wetlands and locations relatively inaccessible for motorboats. Ecological studies in the Mamirauá SDR  have  shown  that  only  once  breeding  populations  in isolated fl oodplain lakes reach levels approaching carrying capacity do Black caiman start appearing in more accessible fl oodplain  wetlands  and  rivers  channels  where  spotlight counts are usually conducted.

However, in areas of varzea habitat in the western Brazilian Amazon, Black caiman can be seen in extremely high densities in  the  seasonal  dry  period  when  many  of  the  temporary floodplain wetlands dry up and caiman move into areas of more permanent water. For instance in some sectors of the Mamirauá SDR, dry season densities in excess of one black caiman  per  meter  of  shoreline  have  been  reported  (>1000 caiman/km). However, it is unlikely that densities of Black caiman from areas like Mamirauá can be used for extrapolation to estimate the population for the entire Brazilian Amazon, as was done to derive population estimates of 8 million M. niger in Brazilian Amazon varzea habitats (300,000 km2) and 16 million in the entire Brazilian Amazon (Brazil 2007).

*This image is copyright of its original author

IN BOLIVIA.

Black  caimans  were  historically  widespread throughout northern and eastern Bolivia, in the Departments of La Paz, Pando, Santa Cruz, Beni and Cochabamaba, but were  heavily  impacted  by  skin hunting during the period 1942-1960 (Plotkin et al. 1983). Surveys in 1986-1987 found M. niger to still be distributed throughout most of its historical range, but in very low numbers (King and Videz Roca 1989). Of the very few individuals that were encountered, most were juveniles or sub-adults. Recent surveys in certain parts of the Beni and Santa Cruz lowlands indicate that populations in some areas are still locally abundant. The species was found to be relatively abundant within the Beni Biological Station protected area (Pacheco 1993a). Encounter rates in six lagoons ranged from 0.47 to 19.5 individuals/km. The numbers of M. niger in rivers were lower (to 1.4/km), but Pacheco (1993a) considered the Beni Biological Station to harbor an important population of this species.


IN COLOMBIA.

Melanosuchus niger was once abundant throughout the Colombian Amazon region in the upper Amazon River and its major affluents, the Putumayo and Caquetá, as well as in the Atacuari, the Loreto Yacu and the Apaporis Rivers, among  others.  According  to  Medem  (1981) commercial hunting for M. niger skins began in the upper Amazon River around 1945 and spread to the rest of the country, causing a rapid decline in its populations. By the late 1950s Black caiman was rare, but it wasn’t until 1968 that the Ministerio de Agricultura limited hunting and egg collection (Resolution 411); a complete ban was put in place in 1969 (Resolution 573) (Medem 1981; Brieva 2002). However, due to poor law enforcement, an estimated 61,116 skins and 259 live animals were exported through Leticia, Bogota, Barranquilla and Cali in 1970 and 1972 (Medem 1981). Medem (1981) concluded that M. niger had virtually disappeared from the Colombian territory.


IN ECUADOR

Asanza  (1992)  reported  that M.  niger heavily exploited in Ecuador between 1930 and 1970, with approximately 500,000 skins being traded, mostly through Leticia  and  Manaus.  In  the  1970s, Medem  (King  1973) believed that Ecuador was the only place where M. niger not on the verge of extinction. In the late 1980s, an illegal trade in small (40-120 cm) live M. niger was reported. Although M. niger was reported. Although their final destination is unknown, numbers of these animals were reported to be exported illegally over the Colombian and Peruvian borders (Asanza, pers. comm.).

Populations  are  known  to  exist  in  several  parts  of  the Ecuadorian Amazon,  particularly  in  isolated  oxbow  lakes. Hines and Rice (1992, 1994) conducted surveys in Ecuador during  the  early  1990s  along  18  survey  routes  (131.2  km total) of optimal habitat. Black caiman were observed at 16 of  17  locations  and  densities  ranged  from  0/km  to  13.25/km,  with  a  mean  value  of  4.65/km.  The  highest  densities were  found  at  Challuacocha  (11-13/km),  Imuya  (<13.25/km), and Limoncocha (10.25/km). In a total of 28 surveys, 309 M. niger  and  188 M. niger  and  188 C. crocodilus  were  observed.  The size  class  distribution  reflected an abundance of juvenile animals. In Limoncocha, Asanza (1992) reported a decline in the population of M. niger between 1983 and 1990. Recent surveys in the same locality report densities of up to 8.27/km, suggesting that the population has been stable during the last few years (Villamarin 2006a).


IN FRENCH GUIANA.

In French Guiana, M. niger is restricted to the coastal region in the northeast of the country. Habitats are the seasonally flooded grasslands of the Kaw River, Angélique and Pointe Béhague, and the mangroves of the lower parts of the Kaw and Approuague Rivers. Before extirpation by poaching during the 20th century, M. niger in French Guiana had a wider distribution, estimated to be two-fold larger than now.

Surveys in the central part of the Nature Reserve of Kaw, which  is  remote  and  inaccessible,  showed  high  densities and age-structure compatible with a healthy population. In contrast, surveys  in borders  of  the  areas  revealed  absence of hatchlings and large animals, and dramatically decreased densities (B. de Thoisy, unpublished data). Analysis of both nuclear  and mitochondrial DNA suggested a high genetic diversity and a significant recovering potential (Farias et al. 2004; de Thoisy et al. 2005; Vasconcelos et al. 2008). Nuclear markers  suggested  that  gene  flows are  important  between Angélique and Kaw River. On the other hand, animals from the Approuague  would  be  related  to  breeders  from  Pointe Béhague, another large swamp inaccessible area located in the East of the river, close to the border with Brazil.


IN GUYANA.

Medem (1983) reported that M. niger was restricted to the upper  and  middle  Essequibo,  Rupununi,  Rewa  and Berbice Rivers, as well as to two Amazon basin rivers (the Takatu and the Ireng) in Guyana. Gorzula and Woolford (1990) noted a similar distribution but were unable to confirm the reports from the Berbice River. Medem’s (1983) survey found Black caiman to be close to extinction in Guyana following a period of intensive skin hunting. During the period of peak hunting, Guyanese residents would apply for permits, then have Brazilian skin dealers from Boa Vista cross the border and organize hunting parties of local Amerindians (Plotkin et al. 1983). Gorzula and Woolford (1990) reported that large-scale commercial hunting took place from 1955 to 1965, and that most of the skins went out via Brazil. Some hunting was reported into the 1970s.


IN PERU.

Historically M. niger  was  common  throughout  the upper Amazon drainages in Peru, but was depleted by hunting which began around 1950 (Plotkin et al. 1983). Surveys by Otte (1974) found no M. niger along the Sotileja, Heath and Pariamanú Rivers, but some were observed in the upper Río de las Piedras. Based on information from caiman hunters and  skin  buyers,  Otte  (1974)  concluded  that  exploitable populations  were  only  found  in  the  upper  regions  of  the Tambopata, Manú, Piedras and Amigo Rivers. As in other parts of the species’ range, Black caiman were rare in Peru in the 1970s and 1980s, and Plotkin et al. (1983) considered the species to be on the verge of extinction in Peru, but numbers of  animals  began  rebounding  soon  thereafter.  Population surveys were conducted in Cocha Cashu in Manú National Park  beginning  the  early  1970s.  Otte  (1974)  estimated  a population size of 37 in 1971-1972. Similar counts carried out in 1978 suggested a 50-60% increase in population size. A census in 1982 estimated population size to be 213 (Vasquez 1982). During nocturnal counts in Cocha Cashu (4.0 km) by Herron (1985), 99-111 black caiman were sighted (uncorrected population  estimate;  density=  24.74-27.75/km  shoreline), with a population heavily skewed towards juveniles.


IN VENEZUELA.

The presence of  M. niger in Venezuela has not been confirmed and appears to be unlikely. The southernmost portion of Amazonas State in Venezuela includes part of the upper drainage of the Rio Negro, and M. niger is known from downstream sections of this river. However, the habitats along the upper Rio Negro do not appear to be favorable for M. niger (Da Silveira and Thorbjarnarson, pers. obs.). There are two reports that suggest there may be, at least periodically, some M. niger in this region of Venezuela. Donoso-Barros (1966a, M. niger in this region of Venezuela. Donoso-Barros (1966a, M. niger1996b) reported M. niger in Venezuela, citing a specimen from the Rio Negro originating from the region south of Cocuy. Gorzula and Paolillo (1986) noted the imprecise locality data, and cited Medem (1983) for a lack of confirmed specimens from Venezuela. Based on their observations in Bolivar and Amazonas  States  they concluded  that  there  was  no  firm evidence indicating M. niger was found within Venezuela.

King (1991) reported a Black caiman killed just southeast of Puerto Ayacucho (presumably in or around the Rio Cataniapo) in 1967 by Jay Wilson, a caiman skin dealer. King (1991) suggested that this area and other sites in the upper Orinoco be revisited to confirm this record. The basis for some prior accounts of M. niger in Amazonas State may also originate in species lists compiled by anthropologists who erroneously considered the local name of “caiman negro” as referring to M. niger whereas it is typically used for Paleosuchus trigonatus.

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https://pdfs.semanticscholar.org/3faf/7b...8e71e4.pdf

There is no information about M. niger's adaptability to dams (Marioniet al., 2013), but in a few years we will know their effects and consequences. We can intuit that the modification of the natural characteristics of the system will have effects on connectivity or isolation, which are recognized as fundamental factors that determine the distribution of species (Pringle, 2003); but these effects will be directed towards the loss of genetic variability, given that the populations upstream of the rapids are already isolated but contribute with individuals that have different genetic characteristics. However, based on the results of this work, we can say that the greatest consequences of the construction of hydroelectric dams for Black caiman populations will be environmental and ecological. The hydrologic regime will change affecting the cycles of flooding and ebbing of rivers that are related to the reproduction, feeding and distribution of the species; and the nesting areas will decrease or disappear due to the flooding of forest areas for reservoir construction. Thus, it is recommended that genetic monitoring be done over the years so that in the future we can mitigate any effects of these barriers to the genetic health of M. niger populations.

Therefore, in this work we have defined seven important areas for conservation that cover almost the entire distribution of the species. The Western, Central, Eastern, Guyana, Bolivia, Napo and Araguaia groups are the areas where there should be operational units to implement management plans (Figure 17). There are a few locations left blank where it would be important to make sampling efforts to complete the definition of conservation areas. Likewise, it is important that all the areas chosen are large enough (mega reserves: larger than a megahectar), taking into account the displacement capacity of individuals, calculated at least 38 km (Da Silveira et al., 2011); well conserved, because the maintenance of populations by migration in degraded areas is not feasible; and with nesting areas, since areas with high densities of nests also have high densities of adults and sub-adults (Da Silveira et al., 1997). All these factors will allow the development of large populations that are a source of individuals to areas less suitable and subject to strong anthropic pressure.

Figure 17. Map of the seven areas defined for the conservation of the Black caiman (M. niger) along its distribution. The questions indicate lack of data.  The distribution of the species is delimited by the white area. Layer of distribution taken from (IUCN, 2000).

1 - Grupo Napo = Napo Group,  2 - Grupo Oeste = West Group,  3 -  Grupo Bolívia = Bolivian Group,  4 - Grupo Centro = Central Group,  5 - Grupo Guina = Guyana Group,  6 - Grupo Leste = East Group,  7 - Group Araguaia = Araguaia Group.

*This image is copyright of its original author

CONCLUSION

The populations of black caiman (M. niger) present patterns of distribution of genetic variability due to differentiation by isolation by distance and structuring by presence of geographical barriers, which are the most important population dynamics for the species.

The Madeira/Guaporé river rapids act as a barrier for the species restricting gene flow between populations that are above, between and below them, and is only given in a unidirectional way, upstream and downstream.

The Isolation by distance determines a West-East pattern, which means that it is necessary to define operational units, such as reserves, to conserve the genetic variability of the species.

The North-South differentiation highlights an old  connection between the lower Negro River and the lower Madeira River.  These two areas constitute a center of genetic variability species.  Therefore, the definition of operational units will allow the conservation of genetic diversity as well as the evolutionary and historical processes that led to the development of this pattern.

The populations of the Araguaia, Guaporé and Uraricoera rivers constitute differentiated management units because they are isolated biological groups that share a reproduction system within each of them and do not receive individuals from other populations.

The genetic diversity of the species is high when compared to other crocodilian species, although there are isolated populations with reduced diversity.

For species with a wide distribution it is important to cover a large part of it to have more complete information about its dynamics and genetic variability
The current threats such as habitat destruction by hydroelectric construction can affect the distribution patterns of the species. Other threats such as illegal hunting can affect it demographically by decreasing its genetic variability. Reply