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Status of Siamese crocodiles in Cambodia
Status, distribution and ecology of the Siamese crocodile
Crocodylus siamensis
in Cambodia
SAM Han1,2,*, HOR Leng1,2, NHEK Ratanapich1,2, SORN Piseth3, HENG Sovannara4, Boyd
SIMPSON5, Adam STARR6, Sarah BROOK7, Jackson L. FRECHETTE2 & Jennifer C. DALTRY2
1 Forestry Administration (FA), #40 Preah Norodom Blvd., Phsar Kandal 2, Khann Daun Penh, Phnom Penh,
Cambodia.
2 Fauna & Flora International (FFI) Cambodia Programme, PO Box 1380, No.19, St. 360, Boeung Keng Kang I,
Phnom Penh, Cambodia.
3 Koh Kong Cambodian Forestry Administration cantonment, Forestry Administration, Phum 3, Sangkat Smach
Meanchey, Krong Khemara Phoumin, Koh Kong, Cambodia.
4 Fisheries Administration, No. 186 Norodom Boulevard, Sangkat Tonle Basac Khan Chamcar Mon, Phnom Penh,
Cambodia.
5 Copenhagen Zoo, Southeast Asia Conservation Programme, 61 Jalan Ulu Klang, Ampang 68000, Selangor,
Malaysia.
6 IUCN (International Union for Conservation of Nature), 326/25 Sibounheuang 26 Rd., Ban Sibounheuang, P.O. Box
4340, Vientiane, Lao PDR.
7 Wildlife Conservation Society, PO Box 1620 House 21, Street 21, Phnom Penh, Cambodia.
* Corresponding author. Email han.sam@fauna-À ora.org
Paper submitted 13 February 2015, revised manuscript accepted 21 September 2015.
CITATION: Han S., Hor L., Nhek R., Sorn P., Heng S., Simpson, B., Starr, A., Brooke, S., FrecheĴ e, J.L. & Daltry, J.C. (2015) Status, dis-
tribution and ecology of the Siamese crocodile Crocodylus siamensis in Cambodia. Cambodian Journal of Natural History, 2015, 153–164.
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Sam H. et al.
conferences of the IUCN/SSC Crocodile Specialist Group
and other forums during this period, this paper contains
new and updated information that has not been pub-
lished before.
Methods
Determining where crocodiles are present
Every year from 2000 to 2014, between four and eight
trained ę eld personnel searched waterways throughout
Cambodia for evidence of crocodiles. Potential sites were
identię ed by interviewing ę shers and other local people,
studying topographic maps and satellite images, and by
soliciting information from government departments
and non-governmental organisations in every province.
Field teams usually worked in pairs to search the banks
on foot for faeces, footprints and tracks, stopping occa-
sionally to scan the water and banks with binoculars for
crocodiles. When possible and safe to do so, we conduct-
ed night surveys by boat or on foot to search for crocodile
‘eye-shine’ reĚ ected in Ě ashlight beams. Most waterways
were surveyed during the dry season between November
and April, when access was easier and signs less likely to
be washed away.
We measured the maximum diameter of intact faeces
(not broken or squashed) and collected them in indi-
vidual plastic bags for analyses (below). We measured
the length and width of clear, intact footprints using the
Introduction
The Siamese crocodile Crocodylus siamensis is a stocky
freshwater crocodile that rarely exceeds a total length
of 3.5 metres. Adult females are typically smaller, at less
than 2.7 metres (Simpson, 2006). It is Critically Endan-
gered and one of the least known of the world’s 27 croco-
dilians (Bezuijen et al., 2012; Grigg & Kirschner, 2015).
Siamese crocodiles used to be abundant and wide-
spread in rivers and swamps throughout Southeast
Asia, including Cambodia, Indonesia, Laos, Malaysia,
Myanmar, Thailand and Vietnam, but their numbers
fell during the 20th century due to collection for croco-
dile farms, hunting, and habitat loss. By the early 1990s,
Siamese crocodiles were feared to be “eě ectively extinct”
in the wild (Thorbjarnarson, 1992).
Verbal reports from the 1990s suggested that Siamese
crocodiles were still widespread in Cambodia (Nao &
Tana, 1994), but it was not until 2000 that wild croco-
diles were conę rmed during biodiversity surveys by the
Government of Cambodia’s Forestry Administration and
Fauna & Flora International (Daltry & Chheang, 2000).
Since then, individuals and small colonies have also
been found in Laos, Thailand, Vietnam and Indonesia
(Simpson & Bezuijen, 2010).
This paper presents the main ę ndings of ę eld surveys
for Siamese crocodiles throughout the Royal Kingdom of
Cambodia by the authors from 2000 to 2014. Although
we have presented and discussed our research at various
Abstract
The Siamese crocodile is one of Southeast Asia’s most endangered species, and Cambodia is believed to hold the largest
remaining wild population. Between 2000 and 2014, interviews and ę eld surveys were conducted on foot and by boat
to document the species’ distribution, ecology, status and threats. Crocodiles were conę rmed in 35 locations in 11 prov-
inces, each holding between one and 40 individuals. Over 75% of sites and 90% of individuals were found in Southwest
Cambodia, with the largest groups located near seĴ lements of indigenous communities who traditionally revere croco-
diles. We conservatively estimate the national wild population to number approximately 200–400 individuals (100–200
mature adults). Analysis of over 650 faeces revealed a wide variety of prey, with snakes and ę sh being the most fre-
quently recorded. Crocodiles were found in freshwater lakes, swamps and slow-moving rivers, from near sea level to
an elevation of 600 metres. Threats include accidental capture and drowning in ę shing gear, poaching, habitat loss and
degradation, and inbreeding and other risks associated with very small populations. No evidence was found of croco-
diles aĴ acking people in Cambodia. The crocodiles are not reproducing well, with fewer than ę ve nests reported annu-
ally. Trial releases since 2012 indicate that captive-bred crocodiles could help repopulate and reinforce wild stocks, but
they must be genetically tested to avoid releasing hybrids. Good progress has been made in enlisting the cooperation of
local communities to protect key wetlands, but continued eě orts from the government and NGOs are also required to
enable this Critically Endangered species to recover.
Keywords
Camera trapping, community-based conservation, crocodilian, faecal analysis, protection, Southeast Asia, wetlands.
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Status of Siamese crocodiles in Cambodia
method of Daltry et al. (2003). All conę rmed localities
were recorded using GPS and entered into a database.
We also recorded the depth of the water body, the sur-
rounding vegetation type, and evidence of ę shing or
other human activities.
When crocodiles were sighted, we identię ed the
species. Cambodia has two native crocodiles, the other
being the saltwater crocodile C. porosus. The species can
be diě erentiated in the ę eld by various morphological
diě erences, one of the most conspicuous being that C.
siamensis bears a row of four large post-occipital scales
on its neck, which are typically absent from C. porosus in
this part of their range (Simpson, 2006).
Population counts
For every waterway where crocodiles were detected, we
used the evidence from sightings and signs to count the
minimum number of individuals present. Because one
crocodile can leave multiple faeces and tracks, we dis-
tinguished individuals based on the sizes of their faeces
and tracks. For example, if some faeces measured 50 mm
in diameter and others were only 20 mm in diameter, we
inferred at least two individuals were present. Faeces
were assigned to size classes based on their maximum
diameter in millimetres (2.0–4.9, 5.0–8.9, 9.0–12.9, etc.)
and footprints assigned to size classes based on maximum
width in centimetres (forefoot width: 6.0–7.9, 8.0–9.9,
10.0–11.9, etc.; hind foot width: 2.0–4.9, 5.0–8.9, 9.0–12.9,
etc.). Faeces and footprints were measured and included
in the study only if they were intact and undamaged.
Because this method did not distinguish between indi-
viduals of similar size, we increased these counts when
crocodiles of equal size were seen at the same time (e.g. if
faeces in a large size class were found, we conservatively
recorded one large adult, but increased the count to three
if three large crocodiles were actually seen).
We tested the use of camera traps to determine
whether camera trapping could help improve our popu-
lation counts during the dry seasons of 2007 and 2008 in
Veal Veng Marsh (Pursat Province; Reconyx TrailMaster
1550, n = 5, and Non-Typical DeerCam DC-300, n = 5); in
2008 along the Areng River (Koh Kong Province; Reconyx
TrailMaster 1550, n = 6); and in 2010 along the Kompong
Chey River (Koh Kong Province; Reconyx RC55, n = 5)
(Starr et al. 2010). Camera traps were directed at river-
banks used by crocodiles for basking, judging by the
presence of faeces and Ě aĴ ened substrate. Photographs
were used to identify individuals from the spots on their
Ě anks and other distinguishing features: a method com-
monly used for identifying and counting big cats and
other animals (Karanth, 1995; Mendoza et al., 2011) and
recently applied to gharials Gavialis gangeticus (Nair et al.,
2012).
Diet analysis
All faeces found were taken to Phnom Penh and sun-
dried, crumbled by hand and carefully inspected for any
remains of prey. Prey were identię ed to major taxonomic
class (e.g. bird, mammal, reptile, ę sh, crustacean), and
to more specię c taxa where possible. Crocodiles digest
bone and Ě esh, but structures made of keratin (e.g. hair,
feathers, ę
sh scales) and chitin (e.g. arthropod exoskel-
etons) are excreted intact (Daltry et al., 2003).
Nest studies
Sites conę rmed to have crocodiles were revisited between
March and June to search for nests. If present, eggs were
counted, measured, weighed and replaced, taking care
not to turn them (Simpson, 2006). Where possible, nests
were routinely inspected by the authors and/or local
community wardens (villagers trained and recruited to
patrol and monitor four of the most important breeding
sites) to monitor their fate.
To overcome the high natural mortality experienced
by wild eggs and juveniles, headstarting was conducted
for three clutches from nests near the Areng River. Most
of the fertilized eggs from each clutch (10 eggs in 2009, 17
in 2012, and 15 in 2013) were collected, and the 42 hatch-
lings were raised for between one to two years in Prek
Svay (Areng) Village before being released back to the
wild.
Results
Distribution
Figure 1 shows locations reported by local people (white
dots), all of which were investigated in addition to other
areas with suitable habitat. Wild crocodiles were con-
ę rmed to be present in 35 localities in 11 provinces (Table
1; dark dots, Figure 1). Over 75% of the occupied water-
ways, and over 90% individuals were found in South-
west Cambodia, especially in and around the Cardamom
Mountains. In almost all cases, the crocodiles were in
relatively remote areas, far from cities and highways.
All of the conę rmed records shown in Figure 1 are
believed to be Siamese crocodiles, not saltwater croco-
diles. Every individual seen by the authors— including
individuals captured by the project team for radiotelem-
etry studies (e.g. Simpson et al., 2006), caught by ę shers
and poachers, and seen in camera trap images— was C.
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Sam H. et al.
siamensis. Although we cannot completely exclude the
possibility of some tracks or faeces being those of saltwa-
ter crocodiles C. porosus, no proof has been obtained of
this species living wild in Cambodia in recent years (PlaĴ
et al., 2006a; Webb et al., 2010).
Habitat
Crocodiles were found in a wide range of freshwater
bodies, including lakes, swamps and slow-moving rivers,
especially the deep-water sections (‘anlong’ in Khmer).
Most sites had gently sloping banks and a mixture of
open and heavily shaded areas, usually surrounded
by forest. The highest documented site was 600 metres
above sea level in the Central Cardamom Mountains.
A shared feature of all permanently occupied water-
bodies was that even at their lowest water levels during
Fig. 1 Reported and conę rmed distribution of Siamese crocodiles in Cambodia.
the dry season, they contained at least 1.1 metres depth
of water.
Population size
Most sites conę rmed to have crocodiles contained evi-
dence of only one or two individuals, with no juveniles or
nests found to prove they were breeding. Table 1 shows
a list of sites with the minimum number of crocodiles
present. Sites with the largest number of individuals
were re-visited multiple times (every year since 2002 in
the case of Veal Veng Marsh and Areng River, and every
year since 2007 in Chay Reap).
Based mainly on signs, we counted 224 individuals
nationwide between 2000 and 2014, including 26 cap-
tive-bred crocodiles that were released in 2012 and 2014
(see Table 1). This is probably an underestimate of the
total number of crocodile present during the course of
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Status of Siamese crocodiles in Cambodia
Site
No. Name of location Province Year(s) surveyed
Minimum no.
of crocodiles
(all ages)
1 Pursat River (upper) Pursat 2003, 2004 3+
2 Pursat River (lower) Pursat 2003, 2004 4+
3 Peam River Pursat 2004 1+
4 Veal Veng Marsh Pursat 2000–2015 40
5 Koi and Krau Rivers Pursat 2002, 2003 14+
6 Russei Chrum (upper) Koh Kong 2004 1+
7 Russei Chrum (lower) Koh Kong 2006 1+
8 Kiew River (Upper) Koh Kong 2004, 2009 7+a
9 Kiew River (Lower) Koh Kong 2004, 2009 1+
10 Kep River Koh Kong 2002, 2009 10+
11 Tatai River (Upper) Koh Kong 2002 11+b
12 Tatai & Touch Rivers Koh Kong 2002 11+
13 Tatai River (Lower) Koh Kong 2002 5+
14 Areng River (Upper) Koh Kong 2002 1+
15 Areng River (Central) Koh Kong 2002–2015* 30
16 Trapeang Rung Koh Kong 2005 11+
17 Kompong Chey River/ Trapeang Peang Koh Kong 2003, 2007–2015* 36+c
18 Sre Ambel River Koh Kong 2008* 7+
19 Kul River, Botum Sakor Koh Kong 2005, 2009* 1+
20 O’Plai (tributary of Srepok River) Mondulkiri 2005 1+
21 Srepok River (Srepok Protected Forest) Mondulkiri 2003, 2004, 2009, 2010* 8+
22 O’Lieou (tributary of Srepok River) Mondulkiri 2003, 2004, 2009, 2010 1+
23 Sesan River Ratanakiri 2005, 2006 1+
24 O’Lalay River Ratanakiri 2005, 2006 3+
25 Sekong / O’Kampa River Stung Treng 2005, 2006 8+
26 O’Chay River Stung Treng 2005, 2006 2+
27 O’Kandal River Preah Vihear 2004 1+
28 Sen River Preah Vihear 2004, 2007 1+
29 Beung Pradak Preah Vihear 2004 1+
30 Porung River Kampong Thom 2004, 2008* 1+
31 Chi Kreng (Tonle Sap) Siem Reap 2004* 2+
32 Prek Toal (Tonle Sap) Battambang 2004, 2007* 6+
33 O’Talas River Stung Treng 2006 4+
34 Anlong Veng Oddar Menchey 2006 3+
35 O’Te River Kratie 2003 1+
Total 224+
Table 1 Conę rmed crocodile locations and population estimates in Cambodia (2000–2014).
* Sites with nests/hatchlings
a Includes two individuals relocated from Atay River hydro dam site in 2010 and Areng River in 2013.
b Includes nine juvenile Siamese crocodiles released in 2010 (headstarted from a wild nest from the Areng River).
c Includes 26 captive-bred Siamese crocodiles released in 2012 and 2014.
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Sam H. et al.
this study because, as explained in the Methods, tracks
or faeces of equal size were conservatively ascribed to a
single individual unless more were seen. It is also pos-
sible some occupied sites were overlooked, especially
those with only one or two individuals. On the other
hand, some of the records in Table 1 date back to the early
2000s and we are uncertain whether those crocodiles are
still present. Allowing for this, we suggest that Cambo-
dia’s crocodile population currently numbers in the low
hundreds, with likely between 200 and 400 individuals
aged one or more years.
Reproduction
Since 2000, nests and/or juveniles were found in only 11
of the 35 sites in Table 1. A total of 22 nests were found, all
towards the end of the dry season (between March and
May). The mound nests were under trees on the banks
of rivers or ponds and usually in deep shade, apart from
three that were on Ě oating vegetation. The adult females
remained close to the nest throughout incubation. In
several localities, including Veal Veng Marsh and the
Areng River, females were observed re-using the same
nesting sites year after year. Clutch sizes ranged from 16
to 25 eggs. Of the 14 nests whose fate is known, ę ve (36%)
were poached, one (7%) was raided by wild animals, two
(14%) were destroyed by Ě ooding, and the remaining six
(43%) hatched successfully. In one well protected lake
in the Areng Valley, we monitored 23 Siamese crocodile
hatchlings from 2007 to 2008, and found only ę ve (22%)
survived their ę rst year.
Diet
Six hundred and ę fty faeces were sampled from the
three largest known breeding colonies (Veal Veng Marsh,
Areng River and Chay Reap) between 2000 and 2014,
representing all size classes from hatchlings to very large
adults. The contents of the faeces included ę sh (30.9% of
faeces), reptiles (29.6%), invertebrates (detected in 11.5%
of faeces, including ants, beetles, scorpions and crabs),
mammals (4.9%) and birds (3.0%). One ę fth of faeces,
most of them in the smallest size classes, contained no
identię able remains. Reptiles and ę sh were identię ed
chieĚ y by the presence of scales in the faeces. At least
88.1% of the reptiles were snakes (present in 26.1% of
all faeces examined), which were conę rmed from their
ventral scales. Most of the mammal hairs were consistent
with rats or other rodents. The largest documented prey
were adult wild boar Sus scrofa, which we identię ed from
coarse hairs in the faeces of very large adults. Amphib-
ians were not conę rmed, probably because their bodies
were fully digested. However, it is likely that some of the
small invertebrates we recorded had been secondarily
ingested along with amphibians and other insectivores.
Discussion
Current distribution and population size
Historical records indicate that Siamese crocodiles
used to be common and widespread in Southeast Asia
(Simpson & Bezuijen, 2010), but Cambodia’s remaining
wild crocodiles are now largely conę ned to small water
bodies in remote areas (Figure 1). Since 2000, more than
200 individuals have been conę rmed at 35 sites on 30
rivers or wetland systems in 11 provinces (Table 1), but
the national population is small, severely fragmented
and likely declining as some of the river systems have
been subjected to high levels of habitat degradation,
overę shing, and hunting. We failed to detect crocodiles
in more than 50% of sites where crocodiles were report-
edly seen in the 1990s (Figure 1), which may be indicative
of a rapid rate of decline. Many of the sites we found con-
tained only one or two isolated individuals and showed
no signs of breeding taking place.
Among the most important known crocodile sites in
the country are Veal Veng Marsh (Pursat Province) and
the Areng, Kampong Saom (Sre Ambel), Kep, Koi, Pursat,
Sekong, and Srepok rivers. Field surveys and interviews
were conducted all over the country, inside and outside
of protected areas, but most of the sites conę rmed to
have crocodiles were state forestlands in and around the
Cardamom Mountain range, up to 600 metres above sea
level. These cooler, higher elevations may be marginal
habitat for this species, and are probably associated with
slower rates of growth and reproduction than the larger,
warmer water bodies in the lowlands.
Obtaining accurate population counts was not easy.
Crocodile surveys in other parts of the world often entail
quietly travelling by boat at night and using a Ě ash-
light to detect crocodiles from their eye-shine (Bayliss,
1987), but we found this method to be of limited prac-
tical use in Cambodia. Most waterways are too remote,
narrow, swampy or densely vegetated to use a boat, and
Siamese crocodiles are scarce and wary. We often failed
to see eye-shine even in areas where crocodile presence
was conę rmed from fresh faeces and tracks. Our pilot
study using camera traps in Veal Veng Marsh met with
liĴ le success because these crocodiles are wary of unfa-
miliar objects: they stopped using their usual basking
areas when posts were installed to hold the cameras.
We achieved more consistent results by using our novel
method of identifying and counting crocodiles based on
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Status of Siamese crocodiles in Cambodia
the sizes and distribution of tracks and faeces, supple-
mented with sightings, but further research is needed to
test the accuracy of the count data shown in Table 1.
We conservatively counted a total of 224 individuals
between 2000 and 2014, and estimate that Cambodia cur-
rently has around 200–400 Siamese crocodiles in the wild,
approximately half of which are adults. While modest,
these ę gures are higher than the best supported esti-
mates for any other range state (Daltry et al., in press). In
Laos, for example, where surveys using similar methods
were carried out between 2004 and 2008, Bezuijen et al.
(2013) documented only 36 individuals in 13 sites in six
river systems (1–11 individuals per site).
Reproduction
Wild clutches found in Cambodia, Laos and Vietnam
contain between 16 and 31 eggs (PlaĴ et al., 2006b; Cox &
Phothitay, 2008; Bezuijen et al., 2013; this survey), smaller
than the clutches of up to 50 that have been recorded
in captivity (Youngprapakorn et al., 1971). In a study of
captive Siamese crocodiles in Cambodia, PlaĴ et al. (2011)
found the mean incubation period to be 72±3 days and
eggs hatched from early May to mid-August (the rainy
season).
Adult females remain close to the nest through
incubation, and hatchlings may stay with their mother
for more than a year (J. Daltry, pers. obs.). In captivity,
both parents of this species have been observed to vig-
orously defend their nest and young when approached
by humans (John Brueggen, St Augustin Alligator Farm
and Zoo, pers. comm.). In Vietnam, a non-fatal aĴ ack
by a Siamese crocodile on a man ę shing illegally in Cat
Tien Lake in 2008 was inferred to be in defence of nearby
hatchlings (Incident #100-3403, CrocBITE database,
www.crocodile-aĴ ack.info). In our experience in Cam-
bodia, however, wild adults immediately retreated from
view when approached by humans, even when their
eggs were handled or their oě spring made alarm calls.
Nests were found by the authors and our colleagues
in 10 waterways in eight provinces in Cambodia, but the
number of active breeding sites is declining. Fewer than
ę ve nests are reliably reported each year and, while some
nests may go undetected, this is consistent with the low
numbers of juveniles reported in the wild. This low level
of reproduction is not suĜ cient to maintain the wild
population, especially given that many clutches are lost
to Ě oods, predators and poachers. Our observations of
a well-protected nesting site in the Areng Valley found
60% of nests were destroyed by Ě ooding and natural
predators, and only 22% of hatchlings survived their
ę rst year. Low rates of survival are not unusual among
nests and young crocodilians, with some studies report-
ing fewer than 2% of hatchlings surviving their ę rst year
(e.g. Green et al., 2010).
Diet
Siamese crocodiles are generalist predators that feed
on a very wide variety of animals including crabs and
other large invertebrates, ę sh, frogs, reptiles, birds and
mammals, including carrion (this study). The present
study is the largest to date on the diet of this species
in the wild, and our ę ndings are consistent with the
smaller sample in Laos studied by Bezuijen (2010). Faecal
analysis cannot be used reliably to quantify the relative
importance of diě erent prey animals because they vary
in digestibility. However, the very high frequency of
faeces containing snake scales and ę sh scales suggests
these animals form a particularly important part of the
diet of Siamese crocodiles. Future studies could consider
using stomach Ě ushing (Fiĵ gerald, 1989) to quantify the
numbers eaten, compare the diets of diě erent crocodile
age groups and to identify their prey to species level.
Interactions with humans
During interviews with over 2,000 ę shers, district oĜ
-
cials, rangers and other people nationwide, we found
no record of wild Siamese crocodiles preying upon or
otherwise aĴ acking a human in Cambodia. This is con-
sistent with historical observations from the early 1900s,
when this species was still abundant (Smith, 1919), and
with recent ę ndings in Laos (Bezuijen et al., 2006). The
CrocBITE database (www.crocodile-aĴ ack.info) aĴ rib-
utes to Siamese crocodiles only three aĴ acks on humans
over the past century (one each in Thailand, Vietnam
and Indonesia), at least two of which were defensive
and not fatal. All in all, the evidence points to this being
a species that typically hunts small prey and avoids
human contact. Communities that have lived in areas
with Siamese crocodiles for generations continue ę shing,
bathing and swimming in the same waterbodies with
liĴ le hesitation. However, Cambodians living in areas
where crocodiles have been absent for several decades or
longer tend to be fearful of them (Chantha et al., in prep).
It can be no coincidence that the largest remaining
colonies in Cambodia are in areas occupied by indige-
nous peoples (e.g. Veal Veng Marsh and the Areng, Tatai
and Kampong Tachay rivers). Members of certain ethnic
minority groups, including the ‘Por’ people of the Carda-
mom Mountains, believe that crocodiles represent their
ancestor spirits and bring good luck (Daltry et al., 2003).
They believe killing or even disturbing crocodiles can
bring serious misfortune. This may be why crocodiles in
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Sam H. et al.
used in most areas, can drown even large crocodiles, and
many deaths have been reported and conę rmed (Daltry
& Thorbjarnarson, 2004). The relatively recent progres-
sion from natural ę bres to nylon nets and lines has
enabled Cambodian ę shers to leave their equipment in
the water for longer than they did in the past, and makes
it harder for crocodiles to break free.
Habitat loss and degradation— Loss and conversion
of wetlands and adjoining habitats for rice farming and
other forms of agriculture is ongoing. Besides subsist-
ence-level farming, economic land concessions have been
awarded to allow huge areas to be mined or converted to
rubber, oil palm, banana and other enterprises (e.g. Neef
et al., 2013). Even wetlands in protected areas are not
safe from this threat. For Siamese crocodiles, of greatest
concern are the many dozens of hydroelectricity dams
that have been proposed or are under construction, both
in Cambodia and in countries upstream (Ziv et al., 2012).
Such developments are not only associated with habitat
loss and alteration, but with new roads, in-migration of
workers, and other changes that make wildlife more vul-
nerable to illegal activities. In 2011, for example, Forestry
Administration rangers discovered a young wild-caught
Siamese crocodile in the possession of Chinese builders
of the Steung Atay hydroelectric dam in Koh Kong Prov-
ince.
Hybridization with other species of crocodiles— In croc-
odile farms and zoos throughout Cambodia and else-
where in the region, captive Siamese crocodiles have
been hybridized with two other species of crocodiles,
the Cuban crocodile C. rhombifer and saltwater or estua-
rine crocodile C. porosus, on multiple occasions (Jelden
et al., 2005). Hybrid oě spring are fully fertile (i.e. they
are capable of breeding with one another or with other
species) and tend to grow larger and may behave more
aggressively than pure-bred C. siamensis. The number
of farms containing hybrids is unknown, but of the
40 crocodiles whose DNA was analysed from Phnom
Tamao Wildlife Rescue Centre in the past three years
14 have been hybrids (35%) (most of the Centre’s stock
were derived from farms in Cambodia) (Starr et al., 2009;
unpublished data). It is not known whether any hybrids
have been released or escaped into the wild, but they pose
a clear danger to the genetic integrity of wild Siamese
crocodiles. Furthermore, by posing a greater danger to
humans, hybrids could also seriously harm public per-
ceptions of crocodiles in Cambodia. Unfortunately, the
only reliable way to identify hybrids is using genetic
analysis. Currently, these tests are expensive and can
only be conducted overseas (Fiĵ Simmons et al., 2002).
these areas were able to avoid much of the persecution
and poaching that occurred elsewhere.
ConĚ icts can arise, however, when crocodiles break
ę shing nets and other equipment, or prey on small
livestock (CCCP, 2012). The authors were informed of
a number of cases of Siamese crocodiles being killed
in retaliation for killing hunting dogs. Like most wild
animals, crocodiles will bite in self-defence when
trapped, and reportedly some ę shers have been biĴ en
while aĴ empting to catch crocodiles or disentangle them
from nets and hooks.
Summary of threats to Cambodia’s crocodiles
Poaching— Interviewees in many parts of the country
described gangs of crocodile hunters who Ě ushed the
reptiles into nets and dug them out of the river bank
burrows to sell them alive to crocodile farms, especially
during the 1980s and 1990s. Illegal capture and trade
continue to be a severe threat to Siamese crocodiles
in Southeast Asia, with live wild adults fetching up to
US$1,800 each in Cambodia (Daltry & Thorbjarnarson,
2004). According to our interviews and direct observa-
tions, at least 61 wild crocodiles were illegally captured
in Cambodia between January 2001 and March 2004,
more than 10% of the estimated wild population at that
time (Daltry & Thorbjarnarson, 2004). Poaching levels
appear to have fallen (e.g. only three individuals were
reported to be killed or removed alive in 2010: Starr et
al., 2010), but any extraction is a serious concern, given
how few remain in the wild. One factor contributing to
illegal trade is that there are many hundreds of crocodile
farms in Cambodia that are permiĴ ed to rear Siamese
crocodiles, but it is diĜ cult for authorities to monitor
so many farms and ensure none purchases or launders
wild-caught crocodiles (Jelden et al., 2005). Unauthorised
cross-border traĜ cking of crocodiles is also ongoing in
Southeast Asia, despite wild populations being included
on CITES Appendix I (Daltry et al., in press).
Drowning and injuries inĚ icted by ę shing gear— Fishing
occurs in most waterways across Cambodia, including
almost every site in Table 1. Even in protected areas that,
on paper, prohibit the collection of any wild animals,
ę shers are usually at liberty to catch ę sh, frogs and other
small aquatic animals. Fishing is considered to be an
essential subsistence and economic activity for many
rural Cambodians (e.g. Hortle, 2007), but this means
almost all Siamese crocodiles are at risk from ę shing
practices. The most destructive ę shing methods, such
as electroę shing, spear ę shing and the use of explosives
or poisons, are prohibited by law but still continue in
remote areas. Gill nets and hooks, which are lawfully
161
© Centre for Biodiversity Conservation, Phnom PenhCambodian Journal of Natural History 2015 (2) 153–164
Status of Siamese crocodiles in Cambodia
Risks associated with small and fragmented populations—
With an estimated total of 200–400 individuals, Cambo-
dia’s wild Siamese crocodile population falls far short of
the several thousand individuals that most species require
to be viable (Traill et al., 2007). Their low numbers and
fragmented distribution makes Cambodia’s crocodiles
intuitively vulnerable to local extinction due to natural
disasters, other stochastic (chance) hazards and/or loss of
genetic diversity (linked to such problems are lower fer-
tility and reduced resistance to disease) (Gilpin & Soulé,
1986). Small population sizes also make the potential
impact of natural predators more serious. Wild animals,
including wild boar, monitor lizards (Varanus spp.) and
macaques (Macaca spp.), prey on the eggs of crocodiles.
Adult Siamese crocodiles in Cambodia have no known
natural predators (although where their ranges over-
lapped, they may have been aĴ acked by larger saltwater
crocodiles historically), but juvenile crocodiles are easily
captured by monitor lizards, large snakes, storks and
other large wetland predators. Natural mortality rates
are uncertain, but the authors’ limited data indicate only
around 40% of clutches survive to hatching and, even in
protected sites, less than 25% of hatchlings survive their
ę rst year.
In addition, radiotelemetry studies of wild and
released captive-bred crocodiles in the Cardamom
Mountains indicate that Siamese crocodiles could be so
sedentary that even individuals from diě erent sections of
the same river might never meet and breed (Simpson &
Sam, 2004; unpublished data), let alone recolonise vacant
waterways.
Conservation Management and Recommendations
Conserving Siamese crocodiles in Cambodia will require
concerted protection and reinforcement of wild popula-
tions to enable them to increase from the low hundreds
to a more viable size:
Community-based and government protection— Cambo-
dia has made progress in reducing poaching and other
dangers by forming groups of trained local wardens to
monitor and patrol crocodile areas, providing appropri-
ate livelihoods assistance to local communities so they
can avoid damaging wetlands, and developing commu-
nity regulations to avoid using the more high-risk types
of ę shing gear at crocodile breeding sites (Daltry et al.,
2005; Oum et al., 2009). Given that the current popula-
tion of crocodiles is very small and fragmented, such
site-based intervention is critical. However, local man-
agement needs to be underpinned with higher level
government protection and support to ensure people
involved in the illegal capture and trade of wild croco-
diles are caught, penalised and held up as warnings to
others, and to safeguard the most essential waterways
and their watersheds from incompatible developments.
We recommend that at least eight of the best Siamese
crocodile sites in Table 1 should be aě orded special pro-
tection by the Royal Government of Cambodia to ensure
their habitats remain intact.
Reinforcement and reintroduction— The release of
captive-bred and/or headstarted crocodiles is essential
to enable Cambodia’s depleted, fragmented and poorly-
breeding wild population to achieve a more viable size
(Daltry & Starr, 2010). This approach is proving vital
to the recovery of the Critically Endangered Philippine
crocodile C. mindorensis (van Weerd et al., 2010), which
was also reduced to a few extremely small colonies. It
is, however, imperative that the captive crocodiles are
ę rst genetically tested to conę rm they are purebred (not
hybrid) Siamese crocodiles, and that hunting, persecu-
tion and other threats have been suĜ ciently reduced
or removed from the proposed release site (IUCN/SSC,
2013). This means releases should take place only into very
well protected waterways and with the prior informed
consent of local stakeholders. In 2010 the Phnom Tamao
Wildlife Rescue Center established a captive breeding
programme to produce healthy Siamese crocodiles for
release. The breeding programme is still in its infancy,
but pilot releases by the authors of 26 captive-bred croco-
diles in community-protected wetlands in 2012 and 2014
have shown excellent results so far, including high rates
of survival and positive responses from the local com-
munities. Further information on the reintroduction and
reinforcement programme will be published separately.
Education and outreach— If Siamese crocodiles are to
repopulate wetlands from which they have been extir-
pated, it is vital to gain the cooperation of local people
and decision-makers. Surveys in the Philippines have
demonstrated that people living in areas that no longer
have crocodiles are often signię cantly more afraid of
crocodiles than people who are still accustomed to living
alongside them (Merlijn van Weerd, pers. comm.), and
the same paĴ ern has been found from interviews in
Cambodia (Chantha et al., in prep). There is therefore a
need for further outreach using a range of media to raise
awareness of Siamese crocodiles, their protected status
and importance to Cambodia, and to demonstrate that
people and Siamese crocodiles can coexist harmonious-
ly. Villagers in the Cardamom Mountains who protect
their local crocodiles could potentially be ambassadors
for teaching and reassuring others that Siamese croco-
diles are an asset and pose no danger when treated with
respect.
162
© Centre for Biodiversity Conservation, Phnom Penh Cambodian Journal of Natural History 2015 (2) 153–164
Sam H. et al.
In addition, given that this species is scaĴ ered across
multiple sites, all of which require skilful management, it
is very important to continue to share methods, ę ndings
and lessons learned with other organisations and gov-
ernment agencies that are interested in the conservation
of this species and its habitats, both in Cambodia and in
other range states. We hope this paper will be a useful
contribution towards this end.
Acknowledgements
The authors are most grateful to His Excellency Cheng
Kimsun, Director General of the Forestry Administra-
tion, His Excellency Nao Thuok, former Director General
of the Fisheries Administration and now Secretary of
State, Ministry of Agriculture, Forestry and Fisheries,
and His Excellency Ty Sokhun, Secretary of State, Minis-
try of Agriculture, Forestry and Fisheries, for graciously
supporting the many years of research and consultations
that have gone into this paper.
Many other individuals and organisations contrib-
uted valuable information and assistance to the authors,
including hundreds of villagers across southern Cam-
bodia, members of the IUCN/SSC Crocodile Specialist
Group and Re-introduction Specialist Group, Frontier,
Wildlife Alliance, Wildlife Conservation Society, and
WWF. GIS support was provided by Chhuon Phirom
(FFI) and Jeremy Holden provided training and support
on camera trapping. Special mention must be made of
the late Ponn Chamroeun, FA staě member of the Cam-
bodian Crocodile Conservation Programme, and the late
Dr John Thorbjarnarson of the Wildlife Conservation
Society, who was among the ę rst to recognise the plight
of the Siamese crocodile. This paper is dedicated to them.
Conservation management and research on the
wild Siamese crocodiles in Cambodia has been gener-
ously sponsored since 2000 by the Asia Development
Bank, Association of Zoos & Aquariums, BBC Wildlife
Fund, Conservation Food & Health Foundation, Criti-
cal Ecosystem Partnership Fund, Disney Conservation
Fund, members and staě of Fauna & Flora Internation-
al, Mohammed bin Zayed Species Conservation Fund,
Ocean Park Conservation Foundation Hong Kong,
Oren Taylor, the Species Fund and US Fish and Wildlife
Service (Critically Endangered Animals Conservation
Fund), among others.
We also thank Dr Nick Souter and two anonymous
reviewers for their helpful advice on an earlier draft of
this manuscript.
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