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Dermatemys mawii

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA REPTILIA TESTUDINES DERMATEMYDIDAE

Scientific Name: Dermatemys mawii
Species Authority: Gray, 1847
Common Name(s):
English Central American River Turtle
French Dermatemyde De Mawe, Tortue De Tabasco
Spanish Tortuga Blanca, Tortuga Rivereña Centroamericana
Taxonomic Notes: This is the single living species and genus in this family which dates back to the Eocene. A number of synonyms have been published for the species, all obsolete and not used for a long time. The corrected but invalid spelling mawei has been supported by some taxonomists.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2abd+4d ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor(s): Vogt, R.C., Gonzalez-Porter, G.P. & Van Dijk, P.P.
Reviewer(s): Rhodin, A. & Van Dijk, P.P. (Tortoise & Freshwater Turtle Red List Authority)
Justification:
A very conservative generation time of 10 years is assumed here; this is almost certainly an underestimate, when neither age at maturity nor average longevity are known. By analogy from other large riverine turtles (i.e., Batagur, Podocnemis), generation time is likely longer. Exploitation pressures have been and continue to be very high, with populations having collapsed over recent decades and recovery, where possible, being very slow. Assuming a 10-year generation time and 5% annual offtake (both very conservative estimates), populations would decline by 81.5% after 3 generations; however, reduced recruitment as adults are removed would reduce the population even further. See Detailed Documentation for details of distribution, population trends and impacts of exploitation.
History:
1996 Endangered
1994 Vulnerable (Groombridge 1994)
1990 Vulnerable (IUCN 1990)
1988 Vulnerable (IUCN Conservation Monitoring Centre 1988)
1986 Vulnerable (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: Inhabits the regions within the large rivers from the Papaloapan basin in central Veracruz and along the lowlands of the Usumacinta basin in the States of Tabasco and Chiapas, as well as in Campeche, Mexico, through Belize and the large rivers and lakes of the department of Peten on the Atlantic coast of Guatemala. There are no records for this species in either the State of Yucatan or in the northern part of Quintana Roo (Iverson and Mittermeier 1980, Iverson 1992, Campbell 1998, Vogt unpublished data). (See Figure 1 in the attached PDF for a map of the extent of occurrence).
For further information about this species, see 6493_Dermatemys_mawii.pdf.
A PDF viewer such as Adobe Reader is required.
Countries:
Native:
Belize; Guatemala; Mexico
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: In the 1970s populations in Tabasco near Villahermosa were decimated and the professional turtle hunters began to go farther and farther away to find turtles to harvest. Harvest quantities in the 1970s amounted to 1,000–2,000 turtles per lake annually; the species was abundant enough in the Tio Lacantum area, Chiapas, that traders built an airstrip to fly them out to Villahermosa (Alvarez del Toro et al. 1979). Tales were told by locals of 100s to a thousand Dermatemys taken in a single day in oxbow lakes along the Rio Lacantun and Lago Palestina near Juarez, Chiapas (Vogt unpublished data). By the 1980s no such large populations remained, and the largest confiscations were rarely over 100 turtles. By 1990 Vogt (pers. obs.) never saw more than 5 animals in one place being held from confiscation or for sale. In the Rio Tsendales, Selva Lacandona, Chiapas, in the 1980s, it was possible to catch 40–45 adults in 5 days of trapping with 20 fyke nets (Vogt unpubished data). By the mid 1990s this population had been decimated by Tabascanian turtle trappers, even though the area was completely within the Montes Azules Biosphere Reserve (Vogt pers. obs.).

Populations of Dermatemys are now so low in Mexico that recovery is perhaps not possible in most regions. The only viable populations of Dermatemys currently (in 2005) exist in inaccessible areas far from civilization. In the Rio Blanco of Veracruz there exists a recuperating population, with a proportion of subadults to adults that is extremely high. Normally at least 80 per cent of the population consists of adults when the population is not being over harvested (Vogt unpublished data). When there are few adults and few subadults and more hatchlings found than adults the population is in extremely fragile shape. When this population was trapped in the late 1990s it had a majority (80%) of subadults, signifying that the adults had recently been overharvested, but that there was sufficient reproductive stock being produced that the population was judged to be recuperating. How many decades this might take is unknown (Vogt unpublished data).

Dermatemys is legally protected by several laws and international agreements but these regulations have not stopped its capture or consumption, and populations of the species in Mexico have been almost eliminated (Vogt and Flores Villela 1992). In Guatemala the status of the population is not clear (Polisar and Horwich 1994). Moll (1986b) conducted countrywide surveys of river systems inhabited by Dermatemys, and market surveys, in 1983–1984. Polisar (1992) documented population structures in sections of the Belize River exposed to contrasting levels of exploitation, finding adults very scarce in the heavily exploited sections. There are reasonable probabilities that some populations in Belize are now afforded at least partial protection, such as sections of Rio Bravo and Irish Creek, Cox Lagoon, and part of the Sibun River (which is a village-originated Hickatee Conservation Area). While pressures in Belize can be assumed to be high, trends have been less disastrous and declines less rapid than in Mexico.

In Guatemala the status of the populations are not known (Polisar and Horwich 1994). A herpetofauna survey of Laguna del Tigre, Peten, Guatemala, in April 1999 focused on Morelet's Crocodile but also recorded the occurrence of Dermatemys, though in densities too low to quantify reliably (Castañeda Moya et al. 2000). Further surveys in Guatemala and follow-up evaluations in Belize are a priority.

It was listed in the 1982 IUCN Amphibia-Reptilia Red Data Book as Vulnerable (Groombridge 1982) and has been considered as a high priority by the IUCN Tortoise & Freshwater Turtle SG in its 1989 action plan; it was uplisted to Endangered in the 1996 IUCN Red List.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Dermatemys primarily inhabit the larger deeper rivers and oxbow lakes throughout the year. During the rainy season they will enter the flooded forests and travel up smaller river courses to nest. Often as flood waters recede they will become trapped in oxbow lakes until the next rainy season, since they are so poorly designed for terrestrial locomotion. Even though this turtle is a fast swimmer and is capable of swimming up rapids they often concentrate in the deep pools at the bottom of the river during the day (Vogt unpublished data). Well oxygenated water is preferred, as they have highly vascularized papillae in the larynx which enable them to stay underwater indefinitely, drawing water in through the mouth and exhaling through the nostrils. However anaerobic black water oxbow lakes used to hold large concentrations of Dermatemys that are trapped there after the water level of the river recedes in the dry season. Although Dermatemys will use fast-moving sections of rivers, they often seek respite from the current in the calmer parts of deep pools and are found in association with submerged tree trunks imbedded in the river bottom. Larger turtles usually rest on the bottom and sometimes partially imbed themselves if the substrate is soft enough. Small individuals often seek shelter closer to shore, resting partially imbedded in accumulations of detritus and also hidden amongst the branches of submerged trees. During April and May, the dry season, adult Dermatemys congregate in the deeper waterholes, 6 m or more in depth. During this same time of the year juveniles and subadults can be found along the shorelines of smaller tributaries taking refuge within the branches of fallen trees or mounds of accumulated detritus (Alvarez del Toro et al. 1979, Polisar 1996, Vogt pers. obs.). Populations in Belize are known to enter estuaries (Moll 1989). Dermatemys is an herbivorous turtle throughout its life (Alvarez del Toro et al. 1979, Moll 1989, Vogt unpublished data). It eats a wide variety of aquatic vegetation, fallen leaves and leaf detritus, and fallen fruits from riparian vegetation. Belizean populations are also known to enter estuaries to feed upon mangrove vegetation and sea grasses (Moll 1989).

Females reach maturity between 34.2–42.0 cm, while males become mature between 32.8-38.5 cm (Polisar 1996, Vogt unpublished data). Females grow larger than males; largest size reported is 60 cm and 22 kg (Alvarez del Toro et al. 1979), although none of 567 turtles examined by Polisar (1996) in North-Central Belize during 1989–1990 exceeded 49 cm. No information is available on age at maturity or on longevity.

Nesting begins during the height of the rainy season from September through December when water levels are at their annual peaks; up to three, exceptionally four, clutches of eggs are laid (Vogt and Flores-Vilela 1992, Polisar 1996). Reports in the literature describing the nesting season as March and April (Lee 1969, Moll 1986a) were based on turtles found in the markets that were most likely holding their eggs for an extended period due to their captive condition. Some females may lay their ultimate clutch for the season in late February or early March, but these are anomalies. Vitellogenesis begins in June and July with oviposition from September to March in the Rio Lacantun in Chiapas (Vogt unpublished data).

Nests are excavated within 3 m of the shoreline, usually within 1 m (Alvarez del Toro et al. 1979), often in saturated soil. Nests are often constructed under an overhanging river bank. Since the nests are scattered along a dynamic shoreline during the rainy season they often go undetected by predators. Often nests are exposed by flood waters creating the misconception that this species of turtle lays its eggs underwater (Vogt unpublished data). The earliest nests of the season are often inundated for weeks at a time with no effect on survivorship. Polisar (1992) documented 80–100% hatching success in eggs subjected to more than 30 days of submersion in water. The physiological mechanisms of this emybryonic diapause need to be investigated further.

Up to three clutches were laid per year in Chiapas, with clutch size ranging from 6-16 eggs. Incubation time in the laboratory varied from 115–223 days, this variation is attributed to embryonic dormancy. Diapause allows the eggs to remain at an early developmental stage when environmental conditions are not favorable for development, cool temperatures and flood conditions, diapause is broken by drying of the nests and warmer temperatures. Clutches laid over a 4 month time span hatch synchronously, stimulated by moistening of the soil during the first summer rains (Vogt unpublished data). In Belize Polisar (1992) reported 217–300 days between oviposition and hatchling emergence. Vogt and Flores-Villela (1992) reported that incubation temperatures in the laboratory above 28° C produced all females and temperatures of 25–26° C produced males.
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): D. mawii is perhaps the most endangered species, genus, and family of turtles in Mexico, and possibly elsewhere in its limited range. Currently the greatest threat to this species is the human over-consumption that has driven them to be threatened with extinction. Although some of the habitats where these turtles live have been degraded, over-exploitation started even before habitat degradation. Dermatemys are captured with nets, by free diving and by harpooning. Its sale has been illegal since 1975, but this has not done very much to reduce its capture. In Mexico, Dermatemys sold for up to US$ 10 per large animal (presumably over 10 kg) in 1979 (Alvarez del Toro et al. 1979); it is currently valued at over $40 per kg live weight in Villa Hermosa (Syed pers. comm. with PROFEPA wildlife inspectors in Tabasco 2005). In 1980 animals were still seen in the fish markets of Alvarado, Lerdo de Tejada and Minatitlan; today they are not sold openly in local markets. In Alvarado, their meat is frozen for sale and delivery is by request (Vogt pers. obs.). Turtle traders in Veracruz expressed concern about future supplies as long ago as 1970 (Mittermeier in Alvarez del Toro et al. 1979). Dermatemys are traditionally harvested for consumption in many areas of Belize (Moll 1986b, Polisar 1995). Dermatemys is similarily one of the most valued turtles in Peten, Guatemala, because its meat is considered a delicacy; animals continue to be hunted with nets, harpooned or collected by hand. At recent harvest rates, the species is expected to be driven inevitably to extinction (Campbell 1998). In addition, the depletion of Mexican populations and the high demand for the species in Mexico will inevitably invite smuggling from Guatemala and Belize.

Conservation Actions [top]

Conservation Actions: Dermatemys has been subject to legal protection in Mexico since 1927, as under the Mexican Constitution all natural resources belong to the Nation and can only be exploited with formal authorization/permits. Dermatemys was included in the Mexican Red data list (NOM-059-ECOL 1994) as endangered, making all forms of harvest and exploitation illegal. However, very little is done to enforce the law and few people respect it (Vogt pers. obs.).

In Belize, there is national legislation (Statutory Instrument No. 55, of April 1993) designed to control the level of harvest and establish some protected populations (Polisar 1994). The efficacy of this legislation needs to be evaluated and the nation-wide status of the species assessed.

Dermatemys is protected under Guatamalan law (Campbell 1998) but exact details are not available.

D. mawii is categorized as a highly protected species under the U.S. Endangered Species Act (Code of Federal Regulations, 1987).

Dermatemys is listed on Appendix II of CITES.

Laguna La Popotera, Veracruz, Mexico, was designated a RAMSAR site in 2005 with specific hopes of creating the first extensively managed wildlife reserve specifically for Dermatemys (Horne in litt. to TFTSG RLA, 27Jul 05). The species is present in Laguna del Tigre N.P. in Peten, Guatemala, and was recommended as a focal species for park management (Castañeda Moya et al. 2000).

Currently there are several ex situ populations of this species with which viable breeding colonies can be established in different zoos and farms. Some of these ex situ populations are: Nacajuca, Tabasco, with 880 turtles, La Florida, Veracruz, with 45 turtles, the Veracruz Aquarium with 2 animals, Chicago Zoo with 2 animals, Detroit Zoo with 2 animals, Philadelphia Zoo with 9 specimens, and the Guatemala City Zoo with one animal.

In 2004 a group for D. mawii conservation was established, proposing a program that includes raising the authorities' and people’s awareness on the species, its captive conservation that includes the genetic management of the captive populations, evaluating the wild populations and their habitat, improved enforcement of existing legal protection, promotion of harvest management measures for sustainable use, and the creation of a reintroduction program.

In summary, existing protective measures need to be implemented, populations inhabiting protected areas must be watched over carefully, and careful thought must be given to meeting some, if not all, of the intensive commercial demand for the species by sustainable production from farms.

Citation: Vogt, R.C., Gonzalez-Porter, G.P. & Van Dijk, P.P. 2006. Dermatemys mawii. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 25 October 2014.
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