River Turtle Exploitation: Past and Present

Turtles and their eggs have long served as an important source of food for humans—almost certainly since very early in the evolution of the hominid lineage, and surely for at least the last 20,000 years (Nicholls, 1977). Evidence in the form of shells and skeletal material (some showing burn marks as evidence of cooking) in the middens of Paleolithic aboriginal cultures, and from eyewitness accounts of explorer-naturalists in more recent times is available from numerous locations around the world (e.g., Bates, 1863; St. Cricq, 1874; Goode, 1967; Rhodin, 1992, 1995; Pritchard, 1994; Lee, 1996; Stiner et al., 1999). Skeletal evidence of river turtles, in particular from such locations as Mohenjodaro and Harappa in the Indus Valley (e.g., Indian narrow-headed softshells and river terrapins), Mayapan, and many other Mesoamerican Mayan sites (e.g., Central American river turtles), and Naga ed-Der of Upper Ancient Egypt (e.g., Nile softshell) suggest that river turtles have helped to support the rise of the world's great civilizations as well (de Treville, 1975; Nath, 1959 in Groombridge & Wright, 1982; Das, 1991; Lee, 1996). Their role continues and, in fact, has expanded as human populations have burgeoned and spread throughout the modern world. River turtles have always been too convenient and succulent a source of protein to ignore. Often large, fecund, and easily collected with simple techniques and equipment, especially in communal nesters which may concentrate at nesting sites in helpless thousands (at least formerly), river turtles are ideal prey. Much of the harvesting has been, and continues to be, conducted in relative obscurity in many parts of the world. Occasionally, however, the sheer magnitude of the resource and its slaughter has attracted the attention of literate observers, such as the early explorer-naturalists of the New and Old World tropics. Their accounts have given us some idea of the former truly spectacular abundance of some riverine species, and the equally spectacular levels of consistent exploitation which have brought them to their modern, much-diminished condition. Summaries of the exploitation of the two best documented examples of destruction of formerly abundant riverine species, the Asian river terrapin, and the giant South American river turtle, are provided under their appropriate geographic sections below.

Introduction

The turtle species that dwell in the world’s rivers, play important, but incompletely understood and largely unappreciated, roles in both the ecology of their respective ecosystems, and in the economy and sociology of the human cultures through which their rivers flow. Accordingly, the precipitous decline of many populations from former levels, and the complete extirpation of some species from large areas of their former ranges is cause for alarm by those concerned, not only with turtles, but with the health and welfare of rivers and humans as well. The causes of these declines are virtually all the result of human activities—including those which involve direct predation on the turtles themselves (and their eggs), removal for the pet trade, and those which result in unfavorable changes in their habitats. The fact that no known modern species has yet been driven to total extinction is testimony to the resiliency and fecundity of river turtle species. This is no cause for complacency—many are almost certainly teetering on the brink now and are facing ever-increasing odds against long-term survival. Some species could be even now beyond hope of recovery, their populations sustained for a time by a relatively few long-lived adults without sufficient collective reproductive “power” to thwart the normal and various mortality sources which plague all turtles, and which their sheer numbers had formerly been able to overcome. However, we are still so ignorant of the population dynamics of these species that we know not which, if any, are doomed. It seems preferable, therefore, as we strive to conserve river turtle stocks that we assume the working philosophy that none is in this category, and focus our efforts and resources toward research and conservation action most likely to return even the most endangered species to robust, sustainable population levels. The roots of the current crisis predate history, beginning with our hominid ancestors, and particularly hunter-gather Homo sapiens’ unparalleled capacity to learn and adapt in order to maximize the harvest of all available food resources.

Traditional Exploitation Methods, Efficiency, and Consequences for River Turtles

A wide variety of ingenious methods for collecting river turtles have been developed over time. None requires a particularly high level of technology but many require a great deal of skill, patience, and sometimes physical ability by the collectors, as well as a detailed knowledge of the ecology of the species being sought. Many parallel collecting methods have developed independently in turtle-dependent cultures around the world, leading Nicholls (1977) to state in regard to Bates’s (1863) description of an Amazonian turtle hunt, “With some allowance for small differences in technique, his descriptions provide an accurate image of turtle hunting as it was practiced anytime, anywhere, during the past thousands of years.” We thought that a summary of these techniques with comment upon their variation in different areas and with different species, their effects on populations when this can be ascertained, and examples of their practitioners would be an appropriate addition to our treatment of river turtle exploitation patterns. We will limit our discussion mainly to techniques employed by subsistence and commercial turtlers for obtaining animals and largely omit reference to the growing body of information concerning the collection of turtles for scientific purposes (many of which are largely modifications of the former techniques). For information concerning the latter category the reader is referred to the excellent summary of equipment and techniques by Plummer (1979) and papers by Carr and Marchand (1942), Chaney and Smith (1950), Legler (1960b), Ream and Ream (1966), Wahlquist (1970), Bider and Hoek (1971), Braid (1974), Robinson and Murphy (1975), MacCulloch and Gordon (1978), Iverson (1979), Petokas and Alexander (1979), Vogt (1980b), Frazer et al. (1990), Kennett (1992), Graham and Georges (1996), Jensen (1998), and Kuchling (2003b). Free diving for turtles is of course a time-honored, effective, and nearly cosmopolitan approach to collecting turtles that requires little or no equipment. While diving mask, fins and sophisticated breathing gear certainly enhance the process, they are not required by skilled divers in order to harvest large numbers of turtles.

River Turtle Diversity, Adaptations, and Roles in the River Ecosystem

There are river turtles and then there are turtles that live in rivers; a statement that suggests that the definition of a river turtle may not be as straightforward as it might first appear. It is an issue that must be resolved, however, in determining the scope of the treatment of the group in this book. Complications ensue from both the context in which the term “river” is applied, and from the habitat catholicity of many chelonian species. Our resolution of the first issue is to focus upon the chelonian inhabitants of larger, higher order lotic environments, and to place less emphasis on the treatment of those species that inhabit smaller streams. With a few notable exceptions (e.g., the flattened musk turtle, Sternotherus depressus due to attention by Mount, 1981; Dodd, 1988, 1990, and in press; U.S. Fish and Wildlife Service, 1990; and Bailey & Guyer, 1998), there is so little information available concerning most of these stream dwelling species that there is relatively little sacrificed with this approach. Nevertheless, we shall refer to the limited literature concerning such species when we consider it important to our treatment of river species. As river ecosystems increase in size, however, they also increase in ecological complexity and habitat diversity. While a complete analysis of these ecosystems is well beyond the scope of this book, Welcomme (1979) distinguished between two broad categories of larger rivers that provide habitat for riverine chelonians—the reservoir river and the flood plain (or flood) river. Reservoir rivers are those with generally stable flow throughout the year as a result of even annual precipitation, or the presence of marginal lakes and swamps that store water that may be slowly released into the channel throughout the year. Such rivers (e.g., the lower Zaire) overflow their banks only rarely during periods of exceptional rainfall. Many flood plain rivers have been altered to such an extent by water flow regulation due to dams, dikes, and impoundments that they now more closely resemble rivers of the reservoir type (Welcomme, 1979). The fish communities of reservoir rivers are diverse, trophically specialized, and structured into well-defined food webs (Roberts, 1973).

Conservation, Management, and Rehabilitation

It is interesting to note in Swettenham’s account that the Malays were already practicing conservation methods for the river terrapins in the nineteenth century. By protecting the beaches from poachers and leaving the third laying to hatch, they maintained moderate recruitment to offset the egg harvest. Similar conservation measures existed on the Amazon River in the nineteenth century to protect the heavily exploited giant South American river turtle, including the protection of females and leaving a third of the eggs laid on the beaches to hatch (Goeldi, 1906 in Parsons, 1962; see also a brief history of exploitation patterns of this species in chapter 5, this volume.). Unfortunately, conservation actions such as these have been the exception rather than the rule in human interactions with river turtles. As emphasized in earlier chapters, populations of most riverine turtle species have seriously declined from nineteenth century levels, but unlike the general declines reported for amphibians, most of the causes are obvious. The burgeoning commercial exploitation for food, traditional medicines, and pets, expanding populations of traditional and introduced predators, and extensive habitat destruction exemplified by such practices as sand mining, damming, channelizing, and pollution of flowing waterways have been key factors. We know far better how we reached this state of decline than how we can reverse the trend. Since the early beginnings of river turtle conservation chronicled by Swettenham and Goeldi, a variety of conservation techniques have been tried world-wide. As there are few proven methods, most actions have been based on what seemed logical or was simply cloned from the methods being used in sea turtle conservation programs. The latter may not have been the best approach for as Pritchard warned in a 1980 paper (Pritchard, 1980b) “sea turtle conservation remains without a theoretical framework, and almost all techniques that have been used remain unproven and riddled with paradox.” Conservation methodology is generally divisible into two divergent approaches, one emphasizing in-situ (on site) techniques and the other ex-situ (off site) techniques. The former aim at protecting animals and their habitat while minimizing intrusion into the life history of the target species.

Communities and Habitats

Rivers are dynamic and diverse ecosystems composed of a variety of habitats including the main channel, side channel, flood plain and backwater lakes as discussed briefly in chapter 2. Each habitat typically contains a characteristic assemblage of turtles (herein considered synonymous with a chelonian community). Although riverine chelonians may appear anywhere in the river, most species specialize in one or more habitats where they occur in maximum numbers and biomass. Thus, the various habitats of the river may have similar species composition but the rank abundance for each species will differ. Basic divisions of typical rivers are lotic (flowing water) habitats and the lentic (still water) habitats. Beyond this, habitat divisions involve such physical features as gradient (headwaters versus lower reaches), substrate (sand, gravel, and mud), size (feeder streams versus the river proper), shoreline heterogeneity (wooded, marsh, swamp, etc.) and even temperature. One can expect differences in species composition associated with any of these habitat features. The composition of river turtle communities is affected by the biotic as well as the physical environment of the stream. The presence or absence of lower and higher plants, competing species, or predators can all affect community composition. This chapter is chiefly concerned with assemblages of species rather than the individual species comprising these groups. It will examine the composition of river turtle communities, their ecology, and their evolution. The concept that organisms occur in assemblages of species interacting to produce distinctive community characteristics was neglected for many years in the herpetological literature. Prior to the mid-1960s, most ecological research on reptiles was autecological (Scott, 1982). Nevertheless, a scattering of early papers described chelonian assemblages associated with particular habitats. Evermann and Clark’s biological survey of Lake Maxinkuckee in 1920 included an overview of the turtle community. In 1942, Fred Cagle delineated the species composition and relative abundance of turtles inhabiting six lentic habitats in southern Illinois. In 1950 he published a similar report with A. H. Chaney on ten lentic and two lotic habitats in Louisiana. Tinkle (1959) compared the species composition and relative abundance of species above and below the “fall line” in five United States rivers emptying into the Gulf of Mexico.

Indirect Factors Contributing to Extinction

Damming and sand mining are examples of factors that indirectly damage or destroy populations of river turtles. Direct factors such as human exploitation are typically more obvious causes of population decline and often serve as stimuli to incite conservation action by a concerned public or government. While direct factors typically kill animals outright or at least remove them from the gene pool, indirect factors can surreptitiously reduce their chances for survival by altering habitat or reducing food supplies. As such, they may decimate a population before it becomes obvious that something is wrong. Though less conspicuous than the direct causes, indirect factors are at least of equal importance in determining the ultimate survival of a species. Table 6.1 summarizes the types of indirect factors affecting selected species. Two important types of indirect factors, habitat alteration and species introduction, are discussed below. Habitat alteration implies any change in an animal’s environment, but herein we will consider human or anthropogenic alterations. Anthropogenic habitat changes are not necessarily harmful to every type of turtle. Riverine specialists are more vulnerable to such changes than are eurytopic generalists that occupy a variety of lotic and lentic habitats. Generalists are by their nature adaptable and thus are less likely to be harmed by changing conditions. A study by D. Moll (1980) on the Illinois River illustrates this principle well. The original environment of the Illinois River has been greatly altered as a result of clearing and draining land for agriculture, dumping of municipal sewage (particularly by the Chicago Sanitary District), and the construction of a series of locks and dams by the Corps of engineers to facilitate barge traffic. Moll found that while these alterations had reduced or eliminated populations of Blanding’s turtles, yellow mud turtles and smooth softshells, generalist species such as the common slider, false map turtles, spiny softshells and common snapping turtles were thriving in the altered environment (see also Mills et al, 1966; Bellrose et al., 1977). Similarly, Anderson (1965) reported that commercial fishermen of the Mississippi and Missouri Rivers noted increases in softshells (spiny?) and snappers in areas having moderate sewage pollution.