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Conservation Status and a Progress Report of the Re-introduction Program of the Siamese Crocodile in Thailand

Yosapong Temsiripong Crocodile Management Association of Thailand
336 M6 Surasak Sriracha Chonburi, 20110, Thailand

ABSTRACT: Since the latest comprehensive survey of Crocodylus siamensis in Thailand was in 1993, the wild population status has just been reevaluated. Surveys revealed few remnant populations of less than 10 individuals together in four remote habitats - Kaeng Krachan National Park (KKNP), Pang Sida National Park (PSNP), Khao Ang Ru Nai Wildlife Sanctuary (KARNWS), and Phu Khieo Wildlife Sanctuary (PKWS). Geographically isolated population of crocodiles in all four areas draws an urgent need for augmentation of viable population. Habitat of KKNP and PSNP were demonstrated to meet requirements for Crocodile Habitat Suitability Index. The other two areas are being surveyed. The schedule for pilot release and monitoring program is set for upcoming dry season. Two groups of local conservationists in KKNP and KARNWS areas have been fully supporting the re-introduction program. That suggests help for community outreach and education program in the areas. However, local sustainable development seems far away since most study areas are restricted and remote. The DNA analysis awaits DNA samples from wild-caught animals in study areas and from Cambodia for a comparative test. The main obstacle for Thailand program has been inadequate government support and insufficient funding.

INTRODUCTION The Siamese crocodile has been widely distributed in the low altitude freshwater wetlands of central and eastern Thailand. They appeared to be reduced to non-breeding remnants in marginal habitats. The principal threats are habitat destruction, illegal hunting, and killing as vermin. They have been considered an endangered species based on the small number of specimens remaining in the wild. In IUCN Red List (1971), C. siamensis is categorized as CR: Critically Endangered, Criteria A.1.a. and c. severely decline in numbers and areas more than 80% decline in three generations (Ross, 1998). During a survey in November 1993, Ratanakorn et al. (1994) confirmed the presence of at least one wild adult C. siamensis in Pang Sida National Park and another in Ang Lue Nai Wildlife Sanctuary. Many sightings of C. siamensis in the wild were recorded at Pang Sida National Park. The most recent one was on April 25, 1993, which is an aerial photograph by M.L. Tossawan Tehwakul (Boonyakhajohn, 1999). In Yod-Dome area, a carcass of C. siamensis was discovered after fish bombing by fishermen. Platt et al. (in press) reported a recent photograph of a crocodile in Kaeng Krachan National Park. Historically, sightings of C. siamensis in the wild were common. In Me Yome, Me Ping, and Pasak rivers, it was fairly common, but it did not exist on the upper reaches of the Me Kong (Smith, 1919). Although wild populations are scarce, C. siamensis is abundant in captivity. Tens of thousands of captive populations of C. siamensis provide a significant resource for restoration (Temsiripong, 2001).

The ideal habitat proposed for restocking of endangered species must be within historical distribution of animals (IUCN, 1992). A limited number of papers describe the historical distribution of the species making it more difficult to locate potential release sites. It is apparent that this stage of survey is to locate any remaining crocodile populations in Thailand. A number of C. siamensis and C. porosus have been bred in captivity to provide a basis for recovery. However, the purity of captive-bred animals is questionable especially in hybrids. No genetic analysis exists for any of the captive populations; the degree of heterozygosity within populations and the degree of relatedness between isolated populations are completely unknown.

As the Siamese crocodile disappeared from people's immediate surrounding, so did this experience and tolerance (Dijk, 1999). It is suggested that the crocodile is not a threat to humans as long as he is given ample room to escape. In fact, a leading herpetologist told swimmers and fishermen that they would be safe from a crocodile attack unless they molest the reptile. During the first decade of the re-introduction effort, the chance that a crocodile will injure a human is exceedingly small, due to the low density of crocodiles in the areas and no one is allowed in the release areas (Temsiripong and Ratanakorn, 2001).


Habitat Survey

Four protected areas within historical distribution of C. siamensis are visited and assessed the habitat suitability index (HSI) for crocodiles. The potential criteria are the food availability, basking ground, nesting area, protection, nursery pond, and survival index. The spoil or sub-optimum habitats are not considered.

Crocodile Survey

The technique involves a small team of observer who survey a section of waterway in one direction during the day, noting salient features and hazards, and then return over the same section in the reverse direction at night. The survey transect (the section of mainstream river or creek and any associated side creeks to be surveyed) has to be defined by a START POINT and a STOP POINT. Any side creeks off the mainstream, which are amenable to spotlight survey, must also have definitive stop points. Both banks of the mainstream and any side creeks are surveyed. Time of year and water level that is going to affect the number of crocodiles seen will be recorded. It is important to do surveys at the same time of year. For the best results, the cool dry season is the most suitable time to conduct surveys because the current is always too strong to conduct such survey. At this time of year crocodiles tend to be in the water at night because it is warm relative to the cool, night air. It is crucial to use the same type of light each time an area is surveyed. The choice of light used will be determined by the nature of the waterway to be surveyed. For small narrow creeks with thick vegetation fringing the water edge and a high frequency of bends, it is best to use a powerful hand torch as opposed to a 100W spotlight. Under these conditions the area effectively scanned with the light is usually restricted to distances of 50 m or less. The use of a powerful spotlight creates a glare from light reflected off the vegetation. This may result in "eyeshines" going undetected as they tend to be obscured by the reflected light. Furthermore, crocodile eyes, like cat's eyes, close up in bright light. In wider, more open waterways, where the observer can scan 200-300 m ahead of the boat, a 100W spotlight is ideal. Locations in this study are reported in Universal Transmercator Units (UTM) Zone 47Q as eastings and northings.

DNA Analysis

Blood sample Collection:

Blood (5 ml) was collected without injury to individuals from either an anterior dorsal sinus using a syringe rinsed with heparin. All samples were collected in icebox and sent to laboratory for DNA extraction. DNA Extraction: For blood, the equivalent of 100 ul of crude blood was first suspended in ACK lysis buffer to a total volume of 1.5 ml. This was followed by a proteinase K digestion (62.5 U in 0.5 ml of 20 mM Tris-HCl pH 8.0) at 65oC for at least 3 hrs or overnight follow by two extractions with equal volumes of phenol: chloroform (PC) in a ratio of 1:1 and one extraction with chloroform. The DNA was then precipitated with 95% ethanol, rinsed with 75% ethanol and redissolved in 200 ul, TE buffer.

Quantity and quality' of DNA:

The quantity of DNA recovered from an extraction was determined from the absorbance of the sample at 260 nm. The estimate was refined by comparing the intensity of the fluorescence produced by the sample and by a standard sample of known DNA concentration running on a agarose electrophoretic gel containing 1 ug ethidium bromide/ml, and visualized under shortwave UV light. These gels also allowed us to estimate the size range of the DNA fragments in the samples.

DNA analysis:

PCR amplifications had final concentrations of 50 mM KCl, 10 mM Tris-HCl pH 8, 1% Triton X-100, 1.5-2.5 mM MgCI2, 150 M of each dNTP, 0.5 M of specific primer, 1 unit Taq DNA polymerase and 50 ng of DNA. During optimization, annealing temperature was varied and/or bovine serum albumin (BSA; 250 g/ml) was added. Thermocycling parameters must be 94oC for 2 mm, follow by 30 cycles of 94oC for 1 mm, annealing temperature for 30 sec, and 72oC for 30 sec.

We tested the ability of the primers to produce specific PCR products from DNA of Siamese crocodiles. PCR conditions were identical to those used C. siamensis. Products were assayed 1.5-2% agarose gels. Tests were considered positive when one or two bands of similar size and intensity to those from C. siamensis are produced. Decreasing stringency of PCR increased taxonomic breadth of taxa amplified, but it also tended to increase presence of extra nonspecific bands and smearing.


Kaeng Krachan National Park (KKNP) is located in the Tenasserim Mountains along the Thai-Myanmar border in Petchburi and Prachuab Khiri Khan Provinces of southwestern Thailand (Fig. 1). Encompassing 2,915 km2, Kaeng Krachan is Thailand's largest national park. The topography is characterized by steep mountain ridges with swift-flowing rivers in restricted valleys. Khao Phanoen Thung (1,207 m) is the highest point in the park. The steep topography and lack of roads make access to the crocodile habitat difficult. Semi-evergreen forest is the dominant vegetation with hill evergreen forest above 1,000 m. Surrounding lands are largely deforested, and KKNP protects the Petchburi River watershed, which supplies Kaeng Krachan Reservoir. The Petchburi River is swift flowing with numerous rapids with small number of Siamese crocodiles recently discovered.

Study areas - KKNP, PSNP, KARNWS, and PKNP

Pang Sida National Park (PSNP) is located by The Khorat Hills in Srakaew Province, eastern Thailand (Fig. 1). With 845 km2, the park is dominated by deciduous and evergreen rain forest as well as lowland scrub and open grasslands at the foothills, which reflects past logging activities. Surrounding lands are deforested with agricultural use. The Houy Nam Yen Creek was selected as the survey site due to many evidences of C. siamensis. For example, a crocodile was sighted and photographed from a helicopter there in 1992. And poachers claimed that they used to harvest hatchling crocodiles from the creek as well. The creek located in the western part of the park flows out of the western boundary of the park into surrounding lowland country.

Khao Ang Rue Nai Wildlife Sanctuary (KARNWS) comprises of 108 km2 and encompasses hills covered in evergreen and dry deciduous forests, with open grasslands in the lowlands. In most of the sanctuary, there are several watersheds that eventually flow into river systems well outside the sanctuary. Most creeks dry and break up to form series of small pools in dry season. Klong Ta Kraw Creek was surveyed once in 1993 by Ratanakorn et. al. (1994). The creek is shallow and narrow and superficially seems to be sub-optimum habitats for C. siamensis.

A 2.8-m wild Siamese crocodile in KARNWS

Phu Khieo Wildlife Sanctuary (PKWS) encompasses an area of 1,560 km2 in Chaiyaphum Province, northeastern Thailand, approximately 550 km from Bangkok. The sanctuary comprises a steep-sided plateau ranging from 540 m at its base to 1,310 m at the highest peak. The plateau is drained by five watersheds: Lam Saphung, Lam Nam Chi, Lam Dok, Huai Sang, and Huai Nam Phrom Creek. The latter is the river reported to have a remnant crocodile population. Hill and dry evergreen and dry deciduous forests with open grasslands in lowlands are major types of forest.


Habitat and Crocodile Survey

Kaeng Krachan National Park (KKNP)

A series of survey carried out in the Petchburi River, Kaeng Krachan National Park from dry season 2001 to wet season 2002. The 30 km stretch of river from the watershed to a reservoir is a rapid flow system with couple deep pools. The sighting of C. siamensis in this river has been reported. Two animals were caught there some thirty years ago and put into a farm. However, no reliably positive identification has ever made until recently. A photograph of a 2-m crocodile was recovered from a camera trap. We are able to confirm three locations where signs of crocodiles were discovered.

Live trap used in Kaeng Krachan National Park

First of all, the first camera-trap photograph of a Siamese crocodile from Thailand was taken in March 2001 by a field team from Royal Forest Department and WCS, in the course of a tiger survey. We visited and surveyed the area in early 2002 and found an old footprint at UTM coordinate 0531939 1425677. Next, the fresh sign of a crocodile is a drag mark and a footprint of approximately 2m crocodile at UTM coordinate 0533145 1416876. The size of the footprint is similar to the one previously reported by Platt et al. (in press). The location is approximately 13 km upstream from the site of the photo record. The footprint measures 175 x 125 mm. It was a right rear foot. It situated at the edge of the sandbar where sand is tiny grain. The left rear footprint was not shown distinctly because the substrate is the coarse grained sand. Tail drag lies next to the footprint with 40-mm width. This indicates that the animal is approximately 2m. The crocodile was observed a week before by a helicopter pilot and a wildlife photographer. Several efforts to try to capture a crocodile that was camera-trapped were carried out, but due to the fact that there was no fresh track found at the location. We got a water monitor in one of the live traps (Fig. 2). The species is extremely common in the area and its sign could confuse an inexperienced observer. We also used a combination of snare, rope trap and baited snare.

From the surveys, we were able to verify the photo observation and to visit a fresh track spotted a week before. We could not capture one and that may be because a recent rain that obscure all tail drag and foot print. Observation and sampling of potential prey item prove that this area can support a population of C. siamensis. Protection is above average according to a large number of carnivore species. And the last but not least, a remnant population lives here. KKNP is, therefore, considered as a re-introduction site.

Pang Sida National Park (PSNP)

The first set of surveys provided an update information of a remnant population of C. siamensis in PSNP. The surveys on the main section (16.7 km) of Houy Nam Yen Creek was repeated several times. The whole section of the creek was walked, paddled, and some time just drift away on bamboo raft. Several basking sites were spotted, three of which could have been made by moderate-sized crocodiles or monitor lizards. With the size of 2 m2, these basking grounds are located between Wang Yao and Wang Mon (Start and stop point of line transects). Unfortunately, 72-hour observation failed to locate a positive sign of crocodiles. Two helicopter surveys for nesting activities in dry season were not able to locate a nest.

The surveys for hatchling crocodiles in wet season were carried out during July - August 2002 in the same area and beyond Wang Mon where never been surveyed before by any research team. We located a hatchling drift across the creek at UTM coordinate 0191145 1553582, but due to dense vegetation we were not able to capture it. We also located a footprint measured at 125 x 105 mm. The footprint could belong to a 1.2-m crocodile. We estimated that there is at least a breeding pair, a juvenile, and a pod of hatchling crocodiles. Habitat and food availability is sufficient to support a small population of crocodiles. Through out the entire creek, there are several deep pools, plus the water is running all year round. The depth of the bottom reaches 3.5 m while the range of the width is 2.5-30 m. The slope of the bank is minimum with abundant aquatic vegetation such as Cyperus sp.and Sagittaria sp.

Khao Ang Rue Nai Wildlife Sanctuary (KARNWS)

Several visits were paid to the basking sites (the location is confidential) which belong to one individual (Fig. 3) in Klong Ta Kraw Creek, KARNWS. We almost always find the animal by one of the basking areas. From 120-hour observation during both day and night, the animal usually surfaces quietly and does not panic when he realizes the presence of humans. He, then, submerges upon arrival and leaves only bubble trails on the surface. Twenty minutes thereafter, he comes back up to breathe for 2 minutes and submerges again for another 20 minutes. Water level appeared low and seemed to be lower till the rain falls. In wet season vegetation on the basking ground is dense, which suggests that the animal had not used the site for a while or he basks only in the dry season. Line transects reveal two more basking sites normally used by the crocodile. A number of scatters collected from these sites proved that the animal has sought a much more secluded site to bask and hide away from us. Later analysis of the scatter uncovers the taxons, which normally being preyed upon by a wild crocodile. The majority of preys are freshwater fish such as Probarbus spp., Channa spp., and Clarias spp. Small mammals' fur is accounted for only 5% w/w of the scatter. A skull of Pig-tailed macaque was discovered by a sanctuary ranger near the creek seemed surprised but not impossible that it was taken by C. siamensis. Upper stream is broken in dry season with only two small pools. Downstream the creek runs toward sanctuary border and end at the Si-Yad Dam near park border.

Observation data show that the crocodile lives mostly under water. He is highly secretive. He basks only in the morning after a cold night. Amidst breeding season, the minimum activity suggested that there is only one crocodile in the area. The sex is therefore unknown because in captivity the size of some females does exceed 2.5 m, while this individual is estimated to attain 2.8 m. Habitat suitability for a small crocodile population looks promising, provided that illegal hunting is under control. A few pools in dry season can accommodate just less than 10 crocodiles. Later relocation of crocodiles to other stretches in the sanctuary is an alternative if there is a severe drought. Although intraspecific competition can be high, interspecific competition is minimal due to small number of salvators and other large reptiles.

Phu Khieo Wildlife Sanctuary (PKWS)

Kreetiyutanon and Khumsuk (2002) photographed a footprint with a measurement 220 x 170 mm for a fore foot track and 210 x 190 mm for a rear foot track. Three basking sites were located near Huai Nam Phrom Creek as well. From the measurement, the animal may have a total length of up to 3.5 m. Two more footprints were reported in a different section of the creek. Therefore, at least 3 crocodiles live separately in PKWS. The plan to conduct more surveys in PKWS is set for this dry season. Currently, the current is strong and unpredictable.

DNA Updated Results

We were able to distinguish C. siamensis from C. porosus. We applied the American alligator microsatellite markers to differentiate both species. It is now in the process of cloning a specific microsatellite marker for the Thailand Siamese crocodile. The DNA samples are from captive animals. We expect to capture a wild crocodile in each study area to represent geographical variation in genetic material, in order to check genetic diversity and the range of heterozygosity of potential release stocks. A few groups of captive-bred crocodiles were selected from CMAT members' crocodile farms. Most were tested for purity of gene.

Interview surveys

Interview surveys with park rangers, sanctuary, and local conservationists

From interviews of 38 park rangers from KKNP and PSNP, 14 sanctuary rangers from KARNWS and PKWS, and 145 local conservationists near KKNP, PSNP, and KARNWS, the results show a significant increase in the number of supporter. Figure 4 could be summarized that people tend to support the project if they are well educated by a project coordinator. Although they are reluctant to welcome crocodiles into their vicinity, half of them think that crocodiles may bring no harm to humans. The need for community outreach and education to create a suitable social climate for accepting wild crocodiles is part of the project (Fig. 5). Social work with education program for schoolchildren and community was considered a major strategy. In KARNWS, local people form a group of conservationists. They campaign against construction of pavement road leading to the crocodile site, since they are afraid the poaching pressure would be out of control.


Threats from poachers and aloewood (Aquilaria spp.) collectors with fishing and hunting activities have always been a major problem of wildlife conservation in developing country. Further natural threats such as flooding and interspecific competition are also major problems. Although most areas have suitable habitat, threat to crocodile may hinder the success.

Together with the Royal Forest Department, we plan to minimize threats to the species such as poaching and fishing, and restore or adjust environment to make it suitable for released animals. We emphasize on monitoring the core not the edge habitat of release areas. We also plan to release the genetic pool that is as similar as possible to the existing wild population. The release of juveniles is in a cause of several years within designated areas. In each area, crocodiles will be released together to make certain that they will not disperse to the distance that make social gathering, mating, and monitoring almost impossible.

Every precaution has been taken to make this re-introduction program the best conservation tool for Thailand Siamese crocodile. Everything that goes into this program has been checked and rechecked to insure long-term survival. We, therefore, sincerely hope that every step of the program will be successful. It is evident that this is going to be a long term and quite slow process, but we agree that the careful and cautious approach is likely to address some of the deep institutional and cultural issues around crocodile re-introduction in a successful way.


1. Continue promoting sustainable use of captive-bred crocodile products, which is part of "wildlife trade campaign" by WWF-Thailand to stop illegal trade of wild fauna and flora.

2. Royal Forest Department and Thai government must enforce protection to minimize poaching and fishing pressure. Today, National Park Division is budgeting the tourist infrastructure to promote many pristine tourist spots in most parks. This could bring an end to poaching behavior.

3. Expand an already established market-driven conservation program to the greater extent

4. Risk assessment must be conducted to evaluate the risk involved within project and from local communities, in order to increase public awareness.

5. A re-introduction workshop needs to be set up with representatives from the Royal Forest Department, Fisheries Department, Mahidol University, NGO, breeders, producers, and leather industry to discuss the following issues: wild population status, in-situ management, effort of market-driven conservation for Thailand program, and local sustainable development.


We wish to thank Dr. Plodprasop Suratsawadi, DG Royal Forest Department, for the research permit to conduct a study in protected areas. Dr. Napawan Nopparatnaraporn's help with DNA analysis is greatly appreciated. Special thanks go to Sriracha Farm Group for technical support and training for sanctuary rangers. We further want to thank all park and sanctuary rangers who assisted in series of surveys. FFI 100% Fund no. 02/21/06FLAG, YAP, NGTV, and CMAT grant no. 4401 and 4501 were sources of funding for the research. Finally, we would like to thank Dr. Robert Mather, WWF-Thailand for pioneering "The Wildlife Certification Scheme" to help prevent illegal trade of wildlife and promoting sustainable use of captive-bred animals that leads to market-driven conservation.


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Crocodile Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK. Viii + 96 pp. Smith, M. A. 1919. Crocodilus siamensis. Journal of the Natural History of Siam. Vol. 3, No. 3.

Temsiripong, Y. and P. Ratanakorn. 2001. A review for reintroduction program of Siamese crocodile in Thailand. Proceedings of the Regional Working Meeting of the Crocodile Specialist Group, Guangzhou, China, IUCN - The World Conservation Union, Gland, Switzerland and Cambridge UK. Temsiripong, Y. 2001. Re-introduction of the Siamese crocodile. CSG Newsletter; V.20, No.1: p.10-13.

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