|Scientific Name:||Tomistoma schlegelii|
|Species Authority:||(Müller, 1838)|
Crocodilus schlegelii Müller, 1838
|Taxonomic Notes:||The evolutionary relationship of Tomistoma with other crocodilians was debated for many years, and the species was usually aligned with the true crocodiles (Crocodylidae) based on morphological evidence (Norell 1989, Tarsitano et al. 1989, Brochu 1997). Molecular studies since the 1980s suggest a closer relationship to Gavialis (Densmore 1983, Densmore and Dessauer 1984, Gatesy and Amato 1992, Harshman et al. 2003, McAliley et al. 2006). A recent molecular study found that Tomistoma shares gene sequences with Gavialis which are absent from Crocodylus, Mecistops (see Shirley 2010) and Osteolaemus, suggesting Tomistoma should be placed within the family Gavialidae (Willis et al. 2007).|
|Red List Category & Criteria:||Vulnerable A2cd ver 3.1|
|Assessor(s):||Bezuijen, M.R., Shwedick, B., Simpson, B.K., Staniewicz, A. & Stuebing, R.|
|Reviewer(s):||Ross, J.P., Manolis, C. & Stevenson, C.|
This species qualifies as Vulnerable as global populations have been reduced, almost certainly by over 30% in the past 75 years / three generations (assuming a generation time of 25 years), principally due to continuing loss and fragmentation of swamp forest over the past three to four decades. Tomistoma schlegelii persists over a wide range (confirmed localities in Borneo, Sumatra and Peninsular Malaysia), but many documented populations are small, fragmented, and under threat from habitat loss. The largest remaining–and most secure–subpopulations may be in East and Central Kalimantan, which support thousands of square kilometres of degraded but largely undeveloped wetlands. Given this, it appears unlikely that <2,500 mature individuals remain globally (the IUCN definition for Endangered), as a relatively small number of sites with small subpopulations (e.g. 50 sites each with 50 individuals or 100 sites each with 25 individuals) is required to meet this criterion. The previous IUCN Red List status (vers. 2.3) for this species was Endangered (Crocodile Specialist Group 2000): the current downgrade in global status to Vulnerable does not imply an increase in the global population/range or a reduction in threats, but a more accurate assessment than was previously possible. Nonetheless, it remains possible that T. schlegelii qualifies as globally Endangered, due to ongoing habitat loss and degradation. At the national and/or site level, this is almost certainly the case for some range states, particularly Malaysia. T. schlegelii was accorded the IUCN Red List status of ‘Endangered’ in 1998 at an expert workshop during the 14th Working Meeting of the IUCN SSC Crocodile Specialist Group. Since that time, new survey data for sites in Kalimantan, Sumatra and Peninsular Malaysia have become available, enabling a more accurate assessment of global threat status. The global status of T. schlegelii is reassessed to be Vulnerable. This is largely based on inferences about habitat loss, rather than documented changes in abundance, because little quantitative data is available for the species. Most surveys have recorded low densities of individuals. Documented examples of population decline include a site in Sumatra, where an increase in logging and burning coincided with a decline in T. schlegelii densities over a seven-year period (Bezuijen et al. 2002), and a park in Kalimantan, where T. schlegelii densities were higher in intact swamp forest than nearby degraded areas (Simpson 2004, Auliya et al. 2006). The species is cryptic and difficult to detect, and rapid assessments may under-record or fail to detect the species, leading to inaccurate conclusions of status. In some parts of Kalimantan, T. schlegelii appears to maintain reasonable levels of abundance even after many cycles of logging and burning in peat/freshwater swamps; in other areas, surveys and local information clearly indicate the species has declined. The principal threat to T. schlegelii is severe and continuing loss of swamp forest, mainly due to logging, fire, drainage, and plantation development. Other threats include entanglement in fishing gear, low-level opportunistic removal of T. schlegelii from the wild, usually by residents and crocodile farmers, who keep juveniles or eggs as items of curiosity, and potentially climate change, which may result in large-scale modification of nesting habitats. Many river systems remain unsurveyed for T. schlegelii and it remains one of the least known crocodilians.
Reasons for Change A downgrade in IUCN Red List status from Endangered to Vulnerable is warranted because surveys indicate the species persists over a wide global range. It has clearly declined in many areas and ongoing habitat loss suggests these declines are continuing.
Tomistoma schlegelii historically occurred over parts of Indonesia (Müller 1838, Weber 1890, de Rooij 1915), Malaysia (Boulenger 1896, Annandale and Robinson 1904, Smith 1930) and possibly Thailand (Taylor 1970). Unconfirmed reports are from Sabah (Borneo) and Viet Nam but are vague and inconclusive (Stuebing et al. 2006). The current distribution of T. schlegelii extends over lowland regions of eastern Sumatra, Kalimantan and western Java (Indonesia), and Sarawak and Peninsular Malaysia (Malaysia), within five degrees north and south of the equator (Stuebing et al. 2006). The species was recently confirmed to occur in Brunei Darussalam. The largest extant populations are in Kalimantan and Sumatra. Most documented populations are diminished and fragmented. Previous reviews of global distribution are by Sebastian (1994) and Stuebing et al. (2006). Summaries of national distribution are as follows.
Brunei Darussalam: Few crocodile surveys conducted to date (e.g. Das and Charles 2000, Cox 2006) and possibly none targeting inland swamp forests, where T. schlegelii are most likely to occur. A crocodile photographed by an expatriate resident in 2005 at Tutong River was confirmed by RBS (from examination of the photograph) to be a T. schlegelii (Stuebing et al. 2006). There is no reason to suggest this was a released individual and it is the first confirmed national record.
Java – status unclear. Koningsberger (1913: 376) noted (in translation) ‘whether, apart from C. porosus, T. schlegelii also occurs in Java, is a question that cannot be answered with certainty..’. Meer Mohr (1921) noted (in translation) ‘according to Strauch, T. schlegelii occurs in Java…the only specimen from Java is in the museum in Stuttgart [Germany]...the origin of this specimen is uncertain...further work is required to clarify the status of T. schlegelii in Java..’. More recently, unconfirmed local reports of T. schlegelii have been obtained from one site, Ujung Kulon National Park (Auliya 2002). The most detailed account of crocodiles for this park is by Hoogerwerf (1970), who does not mention the species. Given the small size of the park and modified nature of surrounding lands, any populations are presumably small.
Kalimantan – confirmed records are from Tanjung Puting National Park (Central Kalimantan Province; e.g. Galdikas and Yeager 1984, Galdikas 1985, Simpson 2004, Auliya et al. 2006), the Mahakam and Belayan river systems and Mesangat Lake (East Kalimantan Province; Endert 1927, Meijard and Sozer 1996, Ross et al. 1998, Staniewicz 2011) and upper Kapuas river area, Danau Sentarum and Gunung Palung National Parks (West Kalimantan Province; Bezuijen et al. 2004 and references therein; Simpson and Mediyansyah 2009); no conﬁrmed wild records from South Kalimantan Province. The species is likely to persist in many other locations in Kalimantan, and the limited number of confirmed localities probably reflects low sampling effort.
Sumatra – all known records are from eastern Sumatra, east of the Barisan Mountain Ranges (Bezuijen et al. 1998). Scattered populations persist from North Sumatra to South Sumatra Provinces, with an isolated population in Way Kambas National Park (Lampung Province). The range of T. schlegelii in Sumatra has declined by at least 30% since the 1950s due to hunting and habitat loss (Bezuijen et al. 1998).
Malaysia: Small populations persist in Peninsular Malaysia and presumably Sarawak (Malaysian Borneo; historical localities include Batang Lupar, Simunjan, and Ensengai). Peninsular Malaysia – confirmed localities are in the Perak and Pahang Rivers, Selangor swamp and Tesak Bera Ramsar Site, all in the western portion of the peninsula (Stuebing et al. 2004, 2006; Bezuijen et al. 2012). Hatchling T. schlegelii observed at a wildlife trader’s facility in 1997 were reported to be wild-caught, suggesting breeding persists in the peninsula (Bezuijen et al. 2012). Remnant populations are almost certainly under severe threat given extensive and continuing loss of lowland swamps and high human densities of this region (authors pers. obs.). Sarawak – status unclear; reported (but largely unconfirmed) from Kuching, Bintulu and Miri Divisions. Sabah – unconfirmed local reports; no other information available (Stuebing et al. 2006).
Thailand: Status unclear. Reported to have occurred (e.g. Smith 1916, Taylor 1970) but records vague and inconclusive. No reports since at least the 1970s; previous authors have postulated the species may be extirpated (Humphrey and Bain 1990, Ratanakorn 1994) or that historical records may have referred to localities in northern Peninsular Malaysia (Stuebing et al. 2006).
Viet Nam: Status unclear. A wild crocodile captured in 1967 was reported to be this species (Mucelli 2005). Given the severe threats facing two confirmed crocodile species in Viet Nam, Crocodylus siamensis and C. porosus, it seems likely that even if T. schlegelii was historically present, it has been extirpated.
Native:Brunei Darussalam; Indonesia (Jawa, Kalimantan, Sumatera); Malaysia (Peninsular Malaysia, Sabah - Possibly Extinct, Sarawak)
|Range Map:||Click here to open the map viewer and explore range.|
No global or national population estimates are available for T. schlegelii. Spotlight densities are the only indices of abundance available for this species and have been documented in relatively few sites. Extrapolation of these densities to larger areas may be unreliable, because densities along rivers or creeks (where most surveys have occurred) may be highly different from swamp forest habitats. This issue is confounded by varying detectability (greater along waterways than within swamp forest). The highest recorded density of T. schlegelii is 1.4-2.6 individuals/km, along a well-protected short (<4 km) river section at the headquarters of Tanjung Puting National Park, Central Kalimantan Province (Simpson 2004, Auliya et al. 2006). This density is apparently atypical for the park: in areas of the park further from the headquarters, habitats are more disturbed and T. schlegelii densities are much lower (Auliya et al. 2006). In Danau Sentarum National Park (West Kalimantan Province), spotlight densities at a site ranged from 0.21 individuals/km in 1994 (Frazier 1994) to 0.08 individuals/km in 2004 (Bezuijen et al. 2004), and 0.02-0.07 individuals/km at other sites (Bezuijen et al. 2004, Simpson and Mediyansyah 2009). At Mesangat Lake (East Kalimantan Province), T. schlegelii is locally abundant; in 2012, densities ranged from 0.2-1.6 individuals/km in flooded forest and open water habitats (Staniewicz 2011). In Sumatra, the highest recorded spotlight densities of T. schlegelii are 0.18 and 0.26 individuals/km, at two sites in South Sumatra and Jambi Provinces respectively (Bezuijen et al. 2002).
Tomistoma schlegelii is a cryptic species and swamp forest habitats are difficult to access: many surveys may have under-recorded or not detected its presence. Compared with spotlight densities for some other crocodilians, which may reach densities of tens or hundreds of individuals per kilometre, all recorded densities of T. schlegelii are low. Repeat spotlight counts at two sites in Sumatra indicate that densities declined over a seven-year period, which coincided with intensive logging and burning in these sites (Bezuijen et al. 2002).
Few other methods to estimate abundance have been applied to T. schlegelii. A mark-recapture study was conducted from 2010-2011 at Mesangat Lake (East Kalimantan Province, Indonesia) but few individuals have been recaptured (Staniewicz 2011). Nest census methods have not been applied to T. schlegelii because nests are located in swamp forest and are highly cryptic.
There is presently insufficient data to estimate the global population of T. schlegelii. Criterion C of the IUCN Red List defines the difference between ‘Endangered’ and ‘Vulnerable’ as the global number of mature individuals to be fewer than 2,500 or 10,000 respectively (IUCN 2001). Whether or not there are fewer than 10,000 mature individuals is unknown. Conversely, there is higher confidence in concluding there are more than 2,500 mature individuals. To achieve a minimum global number of 2,500 mature individuals, a relatively small number of sites with small subpopulations is required e.g. 50 sites each with 50 individuals or 100 sites each with 25 individuals. Given the large extent of swamp forest habitat remaining across the global range of the species (over 13 million hectares of peat swamp in Sumatra, Borneo and Peninsular Malaysia; Yoshino et al. 2010), this seems reasonable.
This generalized conclusion of global status clearly does not reflect trends for all individual range states. East and Central Kalimantan Provinces, which support large tracts of degraded swamp forest, may support the largest remaining populations of T. schlegelii, although surveys are required to confirm this. In at least one site in East Kalimantan Province, Mesangat, preliminary data indicates T. schlegelii persist in relatively degraded swamp forest habitats (Staniewicz 2011). If this is the case elsewhere in East and Central Kalimantan Provinces, the remaining numbers of mature individuals in these provinces may be relatively high. In contrast, survey data from sites in West Kalimantan Province and Sumatra suggest that logging, burning and other human pressures have resulted in reduced T. schlegelii densities. In Peninsular Malaysia, severe and continuing clearance of remnant swamp forest, high human populations, and high levels of economic development, suggest that localized declines or even extirpation may be occurring (see Threats). In Brunei, any remnant breeding populations are probably small, given the small size of the nation and limited extent of swamp forest habitat.
|Habitat and Ecology:||
Tomistoma schlegelii is a freshwater, mound-nesting species. It is among the largest of the extant crocodilians, with males attaining lengths up to 5+ m (Bezuijen et al. 1998, 2004; authors pers. obs.). It is restricted primarily to lowland swamps, lakes and rivers. Most records are from peat swamp and freshwater swamp forest (Stuebing et al. 2006), which historically encompassed most of the lowlands of Borneo, eastern Sumatra, and Peninsular Malaysia.
The ecology of T. schlegelii, including nesting, size and age of sexual maturity, diet, and population demography, remains poorly known. Fewer than 20 wild nests have been documented. Most nests in Sumatra and Kalimantan have been located at the base of large trees in mature peat swamp forest, along remote tributaries (Endert 1927, Bezuijen et al. 2001, Staniewicz 2011). In Sarawak, a nest was located in degraded forest at the edge of cultivated land (Lading and Stuebing 1997). Nests have been reported from floating vegetation mats (Ross et al. 1998). Nesting occurs in the dry season and small clutches (13-41 eggs) are laid (Endert 1927, Bezuijen et al. 2001). Hatchlings emerge in the late dry season / early wet season after an estimated 70-80 days incubation (Bezuijen et al. 1997). Tomistoma schlegelii produces the largest eggs of all living crocodilians (Bezuijen et al. 1998). Sexual maturity in females appears to be attained at around 2.5-3 m total length and 20 years age (Bezuijen et al. 1998, Shwedick 2006, Brazaitis and Abene 2008; B. Ziegler [Miami Metro Zoo, USA] pers. comm. to J.P. Ross 1995; U. Youngprapakorn [Utairatch Crocodile Farm & Zoo, Thailand]) pers. comm. to authors 2008), a relatively large size and late age compared with other crocodilians.
Müller (1838) stated the diet of T. schlegelii comprised fish, monitor lizards (Varanus), waterbirds and mammals. Predation of monkeys by T. schlegelii has been observed (Galdikas and Yeager 1984, Galdikas 1985, Yeager 1991). Stomach contents of juvenile wild T. schleglii included shrimp (Bezuijen et al. 1998) and other invertebrates (Staniewicz and Behler 2010).
Other scientific studies of T. schlegelii have included assessment of its taxonomic status (see Taxonomic Notes), anatomy and skin qualities (e.g. Boulenger 1896, King and Brazaitis 1971, Brazaitis 1973, Fuchs 2006), potential impacts of climate change (Bickford et al. 2010), conservation effectiveness of protected area networks (Rödder et al. 2010), and captive breeding and management (see Conservation Measures).
|Use and Trade:||
Small-scale opportunistic collection of wild individuals and eggs occurs in some regions, for sale to crocodile farms and/or consumption. Previously hunted in some regions for skins and/or meat.
Tomistoma schlegelii is listed under Appendix I of CITES. Captive individuals are held in zoos and private facilities (mainly crocodile farms) around the world, and probably number a few thousand individuals in total. The largest captive population is at Utairatch Crocodile Farm in Thailand (over 700 individuals). Successful breeding has occurred at Jong's Crocodile Farm (Sarawak), Utairatch and Pattaya Crocodile Farms (Thailand), and irregularly at zoos in Malaysia, Europe and North America (TTF 2006, R. Sommerlad in litt.). The provenance of most captive individuals is unclear; many wild-caught T. schlegelii held in captivity may have limited value for conservation purposes unless their original provenance can be determined.
Residents in Sumatra, West Kalimantan and Peninsular Malaysia report that T. schlegelii, as well as other crocodilians, was hunted in the 1950s-1970s for the commercial skin trade, and their meat and eggs were sometimes collected (Bezuijen et al. 1998, 2004; Simpson et al. 1998; Simpson and Mediyansyah 2009). In contrast, hunters in East Kalimantan state the species has no commercial value and was not hunted. Commercial skin trade no longer occurs. Tomistoma schlegelii is not a commercially valuable species due to the presence of osteoderms in the belly scales (farmers in Sumatra, Kalimantan, Malaysia pers. comm. to authors; Fuchs 2006). Low-level but ongoing removal of T. schlegelii from the wild continues. In Sumatra, wild juvenile T. schlegelii at a crocodile farm in 2002 had been purchased from local fishermen, and staff reported that the farm continues to purchase T. schlegelii on an opportunistic basis (MRB unpubl. data). In 1997, juvenile T. schlegelii observed at the facility of a wildlife trader on Penang Island, Peninsular Malaysia, were reported to be wild-caught (Bezuijen et al. 2012). Wild T. schlegelii are frequently observed in captivity along rivers in Kalimantan and Sumatra (e.g. Ross et al. 1998; Bezuijen et al. 2002, 2004; Simpson and Mediyansyah 2009), and are held by local residents as items of curiosity. These individuals are collected on an opportunistic basis and/or are found trapped in fishing nets or traps.
Severe and continuing loss of swamp forest habitat throughout the global range of T. schlegelii is the key threat to most wild populations. Loss and fragmentation of swamp forest has been occurring for over three decades throughout Southeast Asia due to large-scale commercial and illegal logging, plantation development (especially the establishment of paper pulp mills and palm oil plantations), forest fires, and deliberate swamp drainage through construction of channels and dykes. Large areas of swamp forest in East, Central and West Kalimantan were destroyed or severely degraded by the El Niño-induced drought of 1997 and 1998 (Stibig et al. 2007). The expansion of oil palm plantations is currently the main driver of loss of swamp forest in Sumatra and Borneo (Stibig et al. 2007). Based on satellite imagery from 2000, almost 45% (>one million hectares) of peat swamp in Peninsular Malaysia and Thailand has been converted to various land uses, and over a million hectares has been converted in Borneo and Sumatra (Yoshino et al. 2010). Across the global range of T. schlegelii, Borneo retains the largest area of peat swamp under natural cover (70-90%), but which is of varying quality and much is degraded (Yoshino et al. 2010). At least in Sumatra, a significant threat appears to be predation of T. schlegelii eggs by the introduced wild pig Sus scrofa; four of seven T. schlegelii nests recorded along one river were predated by this species (Bezuijen et al. 1997). A smaller but potentially significant threat is opportunistic removal of T. schlegelii and eggs from the wild, usually by residents and crocodile farmers (see Use and Trade). Commercial hunting of T. schlegelii occurred in some regions from the 1950s-1970s and probably contributed to the decline of the species, but no longer occurs. Individuals sometimes drown in fishing nets. In areas with depressed and threatened populations, the continuing low-level removal of mature individuals (e.g. from drowning or capture in fishing gear) may cause disproportionately large impacts; this may be the case along some rivers in southern Sumatra (Bezuijen et al. 2001). Fishing appears to be less of a threat in East Kalimantan (Indonesia) and possibly Sarawak (Malaysia), where fishermen apparently release T. schlegelii caught in fishing gear due to local beliefs that harming the species will bring bad luck or illness (RBS pers. obs.).
Since the 1990s, rapid status assessments for T. schlegelii have been conducted in East and Central Kalimantan (Frazier 1994, Muin and Ramono 1994, Ross et al. 1998, Staniewicz 2011), Central Kalimantan (Auliya et al. 2006, Bonke 2006, Simpson 2004), West Kalimantan (Auliya 2000, Bezuijen et al. 2004, Simpson and Mediyansyah 2009), Sumatra (Bezuijen et al. 1998, 2002), and Peninsular Malaysia (Simpson et al. 1998). Reviews of national or global distribution (Sebastian 1994; Stuebing et al. 2004, 2006) have been prepared. The first dedicated research project on the species was conducted from 1995-1997 and resulted in a status assessment for Sumatra as well as new data on the ecology of T. schlegelii (Bezuijen et al. 1998, 2001). In 2001-2002, largely through the voluntary efforts of MRB and G.J.W. Webb, repeat-surveys were conducted at two sites in Sumatra, and the ﬁrst Indonesian workshop on T. schlegelii was held (Bezuijen et al. 2001, 2002). Sumatran agencies and NGOs subsequently conducted additional surveys which resulted in the discovery of a new nesting site and protection of swamp forest (Bezuijen 2004). These various efforts have resulted in new information on the distribution, status, breeding biology and of ecology of T. schlegelii.
Other initiatives include the following. In 2009, a foundation, Yayasan Ulin, was established in East Kalimantan by RBS to promote wetland and crocodile conservation. This has resulted in co-management agreements with a plantation company to conserve crocodile habitats, support for two international internships studying T. schlegelii and Crocodylus siamensis, and the identification of wetland sites important for biodiversity conservation (Yayasan Ulin 2012). In West Kalimantan, the People, Resources, and Conservation Foundation (PRCF) is planning T. schlegelii conservation activities in Danau Sentarum National Park, to build on surveys in 2004 (Bezuijen et al. 2004). In the nearby Lake Siawan-Belida area, Fauna & Flora International are developing an ecosystem restoration project to manage the swamp forest, including T. schlegelii (Simpson and Mediyansyah 2009). In Sumatra, the non-government organization Wahana Bumi Hijau is implementing a project ‘Protection of the Senyulong crocodile habitat in the Merang-Kepayang peat swamp forest’ [south-east Sumatra]. In 2009 the project received technical assistance from IUCN Netherlands and Mabuwaya Foundation (Philippines) (Weerd and Balbas 2009). In nearby Berbak National Park, the Zoological Society of London is developing the ‘Berbak Carbon Initiative’ to develop carbon markets to protect swamp forest (Suratno and Maddox 2010), which may indirectly benefit local T. schlegelii populations.
In 2010 the CSG Status Survey and Conservation Action Plan was updated, including an update on status and conservation priorities for T. schlegelii (Bezuijen et al. 2010).
Despite these efforts, T. schlegelii conservation is constrained by a lack of long-term research and conservation programs. Virtually all initiatives are conducted with limited funds, often on a voluntary basis, and by virtue of their brief duration have not been sufﬁcient to develop expanded conservation programs. There is a need to assign and fund full-time persons who will coordinate T. schlegelii conservation efforts, including the preparation of funding proposals and lobbying for integration of T. schlegelii into the workplans of provincial governments and international projects.
|Citation:||Bezuijen, M.R., Shwedick, B., Simpson, B.K., Staniewicz, A. & Stuebing, R. 2014. Tomistoma schlegelii. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 25 April 2015.|
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