Peter Paul van Dijk
Zoology Department, National University of Ireland at Galway, Galway, Eire, and Biology Department, Chulalongkorn University, Bangkok 10330, Thailand.
An essay based on a presentation given at the Third World Congress of Herpetology, Prague, 2 - 10 August 1997.
The area now called Thailand, located at the centre of the continental south-east Asian tropical landmass, has been inhabited by turtles as long as turtles exist. It is assumed that this region was part of the Laurasian landmass throughout geological history. Initially it was a coastal region, inhabited in the Triassic Era by one of the earliest turtles ever, Proganochelys ruchae. Turtle fossils have also been found in sediments dating from the Jurassic, Cretaceous, Eocene, Miocene and Pliocene periods and from archaeological excavations.
Biogeographically, Thailand is located where the lndo-Burmese fauna, the Malayan fauna and the Chinese fauna meet and overlap. A few million years ago, Southeast Asia had much of its fauna in common with the Indian region. The enormous Colossochelys atlas tortoise, for example, ranged from western India to Sulawesi and Timor. Fossils show that during the Ice Ages, the temperate Chinese fauna extended further south. When the climate warmed in recent times, a few member species of that community maintained a foothold in Thailand by retreating high on cool mountain slopes; the Big-headed Turtle (Platysternon megacephalum) is one of these species. In addition to these tides of migrating, expanding and contracting species ranges, many species evolved in the area itself. The ever-changing topography of islands forming and re-connecting to the mainland as sea levels changed and the isolation of animal populations on mountains or separate river basins also contributed to give this region one of the richest and most complex faunas anywhere on earth.
Thailand's mountain and hill ranges stretch in a general north-south direction. This is an effect of the squeezing and buckling of land areas as the Indian subcontinent collided into the Asian landmass: This created the Himalayas at the main collision front, and buckled other areas around its edges, just like a fist pushed into a pillow. Because of its location and mountain relief, mainland Thailand's climate is at present strongly seasonal, with a rainy season lasting 5-6 months from May to October, a cool dry period to January and intense humid heat from February to April. The climate is less seasonal in the southern Peninsula. In the recent past, four main forest types have developed in Thailand.
Broadleaf evergreen rainforest occurs in the southern Peninsula. This is the classical rainforest, with enormous, tall trees forming a closed canopy shielding a sparse understorey of lanky shrubs and saplings. The typical turtle species of this forest are the Brown Asian Giant Tortoise (Manouria emys emys) and the Spiny Terrapin (Heosemys spinosa), while streams in the forest are home to the Flat-backed Terrapin (Notochelys platynota), the Stream Terrapin (Cyclemys dentata) and the Malayan Softshell (Dogania subplana).
In regions of mainland Thailand with strongly seasonal rainfall, the corresponding forest type is the seasonal broadleaf evergreen forest, which to a non-botanist looks identical to rainforest. A turtle lover would notice the difference immediately, though: here the Brown Giant's cousin lumbers over the hill slopes, the impressive Black Asian Giant Tortoise (Manouria emys phayrei), while the dazzling Impressed Tortoise (Manouria impressa) inhabits some of the mountain slopes above 600 m altitude. Gentle sections of the forest streams are inhabited by Stream Terrapins and the odd Giant Terrapin (Heosemys grandis), Asian Box Turtle (Cuora amboinensis) or Asian Softshell (Amyda cartilaginea), but you have to climb along the steep rocky trickles high on the mountains to find the amazing Big-headed Turtle.
The mixed deciduous forest type occurs in drier areas than evergreen forest, such as lowland plains and hill slopes on the mountain's lee side. This forest has a rather closed canopy formed by tall trees, but because the trees shed their leaves during the driest part of the year, enough light reaches the forest floor to make it possible for herbs and grasses to grow in profusion. The daily and annual temperature and humidity fluctuations in mixed deciduous forest are quite distinct. The characteristic turtle of deciduous forests is the Elongated, or Yellow, Tortoise (Indotestudo elongata). The streams in areas blanketed by deciduous forest provide enough moisture for narrow galleries of evergreen forest to line the stream, and the turtle species inhabiting these streams are generally the same as occur in and along seasonal evergreen forest streams.
Where forest fires are a regular occurrence and the soil is poor, a subset of deciduous tree species that can tolerate drought and fire will flourish and slowly come to dominate the forest as less resistant tree species disappear. The climax stage of this process, where a very open and low forest dominated by Dipterocarp tree species develops, is named the dry dipterocarp forest. This also has a dense undergrowth during the rainy season, which withers in the dry season and conducts ground fires with dismaying steady progress. Nevertheless, many individual Elongated Tortoises make their home in dry dipterocarp forest.
Finally, some of the best turtle habitats are not forest, but lowland rivers and their seasonal flood-plains and swamps, their estuaries and the sandy sea beaches. It is here that the greatest diversity of turtle species occurs, from the small, harlequin-faced Snail-eating Terrapin (Malayemys subtryuga) and the large yet gentle Yellow-headed Temple Terrapin or Lotus Terrapin (Hieremys annandalii) of quiet swamps to the superlative Striped Giant Softshell (Chitra chitra) of wide, strongflowing clear rivers. Estuaries shelter such rare species as the Mangrove and Red-headed Terrapins (Batagur baska and Callagur borneoensis, respectively) and the Frog-headed Softshell (Pelochelys cantorii), while several species of marine turtles come ashore periodically to lay their eggs in the warm beach sands.
Human presence in Thailand dates back a long time, though nothing comparable to the turtles'. One of our distant relatives, Homo erectus, lived in China and Java between one million and a few hundred thousand years ago, and it is likely that they also inhabited what is now Thailand. In caves in western Thailand, evidence of presumably continuous human occupation exists from Palaeolithic to Neolithic periods, currently understood to range from 500,000 to 3,000 years ago. Excavation results at some cave sites have been interpreted as showing that upland slash-and-burn agriculture existed as early as 10,000 years ago, making this one of the earliest centres of agriculture world-wide. The tantalising glimpses of prehistoric life come in the form of stone tools, little ornaments and other objects, but also cave paintings. The finest of these paintings, dated between 1000-3000 years old, are in north-eastern Thailand on the Pa Taem cliff overlooking the mighty Mekong river, and include an enormous turtle among humans and giant catfish.
Archaeological excavations prove that turtles were on the menu of Stone Age man. Indeed, one professor of archaeology told me that, in the time that he was a student taking part in excavations, he would often get very excited about finding a piece of flat bone looking like a human skull fragment, only to discover at close examination that it was yet again a piece of turtle shell. The bas-reliefs on the walls of the magnificent ancient Khmer capital of Angkor, in present-day Cambodia, depict many turtles as well as freshwater fish and ways to capture them, as well as persons apparently admiring the animals. The habit to consume turtles continues to this day. Collection of turtles for consumption has been so widespread for such a long time that it is not possible to estimate the original, natural population densities of turtles with any reliability.
Forest clearance for conversion to agricultural land has obviously impacted turtles by loss of forest habitat. Selective logging by the timber industry did not have such an extreme effect, but the effects of logging on forest structure are generally not beneficial to turtles. Neither is the presence of labourers, and where logging roads are established, settlers soon follow.
Still, large areas of forest remain in western Thailand, centred on the twin Wildlife Sanctuaries of Huai Kha Khaeng and Thung Yai Naresuan. Together they cover about 6000 square km (2350 sq. Mi.), while several adjacent National Parks and Wildlife Sanctuaries protect another 6000 sq. km. Yet this Western Forest Complex is far from pristine.
Deep within the Huai Kha Khaeng sanctuary, a collapsed circular wall of stacked rocks can be seen. At its centre, two urns containing the skeletons of a man and two women were found by archaeologists. The pottery and small artefacts found with the skeletons show that this burial site dates about 600 years back and the deceased were clearly members of the lowland ethnic Thai culture rather than any of the hill tribal cultures. At that time, the ethnic Thai had settled and established wet rice culture in the fertile flood-plain of the Chao Phraya river, with the great cities of Sukhothai and Ayutthaya the centres of their kingdom. What these people did in the dry, relatively infertile hills of the West, and why they wished to have their elaborate burial there, is unknown.
Almost certainly, the Thai came to the western hills to hunt deer and rhinoceros. Deer skins and rhino horns were valuable commodities, and Portuguese, Dutch and English merchants vied for the opportunities to export them to Japan and the Arab world. In fact, much of our knowledge of daily life in and the economics of the Ayutthaya kingdom is based on the records of European trading companies. Most of the indigenous records were lost when Ayutthaya was sacked by invading Burmese in the 18th Century. The rhinos became extinct somewhere around the middle of this century.
Hunting, at least of deer, probably took place mainly during the dry season and likely involved setting fire to the dry grass and leaf litter to drive the quarry. Some of the ethnic minorities practice slash-and-burn agriculture in addition to hunting and collection of forest produce. Burning of vegetation certainly appears to be a national pastime at present. Certainly, such undergrowth fires have some beneficial effects: they clear the forest floor so people can walk easily, they make mineral nutrients available to encourage grass growth which in turn benefits grazing animals, and fires eliminate tick larvae, which can otherwise occur in plague-like numbers.
Yet as we currently understand it, the overall effects of regular forest litter fires are mainly negative. Numerous small animals perish or get scarred in the flames, while those that survive have to deal with an absence of food, shade and shelter and are easily spotted by predators. Tortoises, especially juveniles, find this a difficult time. The effects of fire on forest structure are more insidious. Fires started by natural causes such as lightning strikes occur on average every twenty years, and occasional leaf litter burns in dry evergreen and mixed deciduous forests can be tolerated by individual trees. However, the accumulating damage at the tree base from annual burns eventually kills most trees and repeated burning will eventually lead to the formation of fire resistant dry dipterocarp forest. Whether this expansion of dry dipterocarp forest in the past centuries has benefited the Elongated Tortoise is not clear, but it certainly occurred at the expense of the Manouria tortoise species.
The human impacts on freshwater turtles were and are completely different and, apart from direct collection and the development of crop cultivation near settlements, of much more recent occurrence. Large scale rice culture quickly spread over almost the entire flood-plain area when rice became an export commodity in the mid-nineteenth century. This eliminated most of the flood-plain wetlands, and now only the names of villages such as 'Village of the Elephant Swamp', 'Hamlet in the Lotus Swamp' or 'Town among a Million Teak Trees' allude to what must have been splendid landscapes. The impact of this loss of wetlands on turtle species is hard to gauge. If we look at wetland birds, we know that several species have disappeared from the region, while others have adapted to the new landscape created by humans and thrived. One turtle species, the Snail-eating Terrapin, probably did just that when it found that the shallow warm water of rice fields and abundance of snails in those fields provided perfect conditions to grow, while the animals could withdraw to the irrigation canals when the fields dry out after the rice was harvested.
In the past 35 years, all but one of Thailand's major rivers have been dammed to create multi-purpose reservoirs, providing non-polluting electricity, storing water for dry-season irrigation and consumption and creating recreational facilities. The general assumption is that such reservoirs are beneficial to wildlife because there is more water available, throughout the year. However, while the total water surface and volume increases, benefiting pelagic fish species, the total area of bankside vegetation of the former main river and its tributaries is replaced by a barren draw-down zone at the reservoir shoreline. Moreover, a thermocline forms in the reservoir water body, creating an upper zone about I0 m (33 feet) deep with warm, moderately oxygenated water. Below this is a mass of colder water where decomposition of vegetation and other material takes place. Because these water layers rarely mix, the deep water eventually becomes completely anoxic and unable to sustain more than bacterial life. When deep water comes to the surface, usually localised during storms, fishkills often are the result. As regards turtles, preliminary surveys (Thirakhupt & van Dijk, 1995) suggested that despite stocking of juvenile turtles, only small numbers of individuals of a few species inhabit reservoirs.
Down river from a dam, the released reservoir water is colder and its oxygen level is about half that of normal river water, due to mixing of surface and deep water. Because dissolved sediment of the inflowing river settled out in the reservoir, the water released from the dam is clear and has a great capacity to remove and transport sediment. Consequently, the river cuts deep in its bed and undercuts its banks, a process called bed scouring. Eventually, the river bed digs itself several metres deeper and the bed becomes 'armoured' by a layer of large boulders. Major cities and attendant industries are usually located alongside rivers and entrust their sewage and much other waste to this convenient conveyor belt. Together with direct hunting, these various habitat impacts have led to severe declines in the population of Chitra softshells, and it is uncertain whether this magnificent species can survive.
Mangrove forests at estuaries and along coasts have been, and in places still are, cleared for charcoal production, prawn aquaculture and coastal industrial development. In the process, spawning and nursery grounds for countless fish, prawns and other animals are destroyed and populations of Pelochelys, Batagur and Callagur turtles are eliminated.
Above, I presented a depressing list of negative impacts on turtle individuals and populations. You will wonder - 'are there any turtles left at all ?' The answer is 'Yes, many, but often in semi-captivity.'
Turtles have been kept in temple ponds for decades, probably centuries, because temple grounds are sacred and free from human collection or other destructive activities. By releasing a turtle or other animal in the temple grounds, which usually included a lotus pond, the animal would be free from human sources of danger. When more than a few turtles inhabit a lotus pond, though, they will munch their way through the lotuses and eventually food may become scarce. People usually do not feel a direct responsibility for the particular turtle they released, but many people like to visit and feeding the turtles is a popular weekend pastime. Left-over fruit and vegetables from the markets are often donated as food for the turtles and other animals. In some temples with large numbers of turtles, one monk is often selected to act as guardian and look after the turtles' interest.
Farming of turtles, almost exclusively the Chinese Softshelled Turtle Pelodiscus sinensis, has become a rapidly expanding branch of aquaculture in the past 8 years. By 1994, the production was estimated to be between 3 and 6 million turtles each year. Many of these are exported to Hong Kong, Taiwan and mainland China as hatchlings for raising, while another part is reared locally and then exported or marketed and consumed locally. Collection of wild turtles for export to China appears not to be a significant threat in Thailand, in contrast to the alarming reports emerging from Myanmar, Laos, Cambodia, Vietnam and Indonesia (Jenkins, 1995).
Thailand has designated over 60 National Parks, open to visitors, and over 30 Wildlife Sanctuaries, which are effectively closed to all people except park staff. In both types of protected areas, all forms of interference and disturbance are prohibited. Together the parks and sanctuaries cover about 12% of the country, including two-thirds to three-quarters of all forest area. Few countries anywhere in the world can match this. Sections of large river with riverside forest is about the only habitat type that is not adequately represented in the system. Viable populations of most turtle species occur inside protected areas. As surrounding countries exploit their turtle populations more intensively than ever happened in Thailand, these protected Thai populations may be the best hope for survival of these species. Much still needs to be done before we can be assured that natural, wild populations of all species are safe, and for a few we may already be too late, but great steps have already been taken in the right direction and there is hope for the future.
Meanwhile, dedicated hobbyists world-wide can contribute significantly to the chances of survival of natural turtle populations. Husbandry skills have improved in the past decades, to the point where careful management of animals currently kept in captivity should be sufficient to maintain permanent, self-perpetuating populations. The 'studbooks' organised by our Dutch sister group, the NSV, are examples of what is possible. Eventually, I hope, this will lead to a situation where exploitation of wild populations for the pet trade is no longer necessary (and possibly legally prohibited) but competent, serious hobbyists can still obtain captive-bred animals of a wide variety of species.
In some cases, captive breeding by zoos and skilled amateurs may prove to be an essential, integral part of a conservation strategy for an endangered turtle species. The Western Swamp Turtle (Pseudemydura umbrina) was pulled from the brink of extinction by skilled captive breeding, and I fear that captive breeding will offer the only chance of survival for some of the Chinese turtle species. We may see a situation, not too far in the future, where captive-bred animals will be returned to their native areas of occurrence, to strengthen depleted populations or re-establish extirpated colonies. There are problems with this approach, including the possible introduction of diseases to native populations, the potential for 'genetic pollution', and the unfortunate cases where the original habitat has been destroyed, and such introductions need to be carefully considered. It appears that none of the turtle species inhabiting Thailand needs this kind of assistance; the most endangered species are also the least suitable for captive breeding, namely the large softshelis (Chitra and Pelochelys) and river terrapins (Batagur and Callagur).
The other effort that hobbyists can and do make to protect populations of wild turtles is by expressing their concerns and mobilising support. The BCG has been particularly active in this arena by cooperating with and providing advice to organisations and authorities to improve protective legislation, by assisting research and practical conservation action and by working for better care of captive tortoises, terrapins and turtles. Our captive animals often work as ambassadors for their wild relatives, stimulating interest and concern among people that will never see a turtle in the wild. Together we can make a change for the better.
Thirakhupt, K., and P. P. van Dijk. 1995. Species Diversity and Conservation of Turtles of Western Thailand. Natural History Bulletin of the Siam Society, Vol. 42: 207-259.
Jenkins, M. D. 1995. Tortoises and freshwater Turtles: The trade in Southeast Asia. TRAFFIC International, Cambridge, UK. iv + 48 pages.
Testudo Volume 1 1979