Orissa, India. Crocodilians show complex social
behaviour. Courting may involve roaring, postural
changes, positioning and snout rubbing, shown here.
Photo by L.A.K. Singh.
Many crocodilians form nests of mounds of vegetation.
Photo by R. Godshalk.
Crocodilians (crocodiles, alligators, caimans, and gharials), are prominent and widespread occupants of tropical and subtropical aquatic habitats. The group is of great antiquity with hundreds of fossil forms and three major radiations. Table 1 shows the taxonomy of the extant 23 species. Crocodilians are implicated in positive effects in their environments as keystone species that maintain ecosystem structure and function by their activities (King 1988, Craighead 1968). These include selective predation on fish species, recycling nutrients, and maintenance of wet refugia in droughts.
Order Crocodylia
Family Crocodylidae
Family Gavialidae
Crocodilians have some unique aspects of natural history that create special challenges for their conservation. They are the largest predators in their habitats and can threaten humans and their livestock. Many species are exploited for their valuable skin, which supports an international trade worth over US$500 million annually. They are also heavily affected by habitat loss and the pollution of aquatic habitats. Loss of any species of crocodilian would represent a significant loss of biodiversity, economic potential and ecosystem stability.
There is a wide diversity of size, habitat, food preference, reproductive behavior and many other aspects of biology among the 23 species of crocodilian. However, all species have the following basic similarities. All crocodilians are very effective aquatic predators. At smaller sizes they often eat aquatic insects, small fish and crustaceans and as they grow larger they tend eat more vertebrates, including fish, turtles, birds and mammals. Crocodiles attempt to maintain their body temperature within narrow limits by basking in the sun when cool and seeking shade when hot. They are metabolically efficient and have fast reflexes and effective locomotor ability on land, where they walk on erect legs, and in the water, where they swim rapidly driven by their powerful tails. Crocodilians have complex behaviors including social interactions, dominance hierarchies, vocalization, coordinated feeding, and well developed maternal behavior. Females deposit from 10 to over 60 hard-shelled eggs into a nest which is either a hole dug into the ground, or into a mound of vegetation formed by the female. Most females remain near their nest during incubation and may protect it from predators. Upon hatching, vocalizations made by the hatchlings induce the female to assist the hatchlings to emerge, and in some cases to carry the tiny babies to the water in her mouth. Hatchlings remain together near the mother for several months, deriving protection from her. As they grow and become more widely dispersed and independent, a large number of the offspring perish some eaten by other crocodilians.
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| Courting mugger, Crocodylus palustris, Tirkarpada, Orissa, India. Crocodilians show complex social behaviour. Courting may involve roaring, postural changes, positioning and snout rubbing, shown here. Photo by L.A.K. Singh. |
Common caiman, Caiman crocodilus, attending nest. Many crocodilians form nests of mounds of vegetation. Photo by R. Godshalk. |
The survivors reach maturity after a period of 515 years depending on the species. Females grow more slowly and reach maturity at a smaller size than males, who continue growing and usually exceed females in maximum size. Crocodilians can be long lived in the wild and there are records of particular individuals residing for decades at some locations. Adults of several species emit loud vocalizations during the breeding season. Details of crocodilian biology as it pertains to their management and conservation can be found in Webb et al. (1987). These biological characteristics give the potential of great resiliency to some crocodilian populations, enabling them to recover from population depletion and sustain relatively high harvest rates. However, unregulated killing of adults can lead to rapid population depletion, particularly if combined with habitat loss.
Identifications and keys to the crocodilian species are given in CITES 1995, King and Brazaitis (1971), Brazaitis (1973) and the CITES Identification Manuals (Dollinger 1983).
Crocodilians are threatened by many human activities. Foremost and the most significant among these is the destruction or alteration of wild habitat. In the past, commercial overexploitation and indiscriminate killing have resulted in many species suffering drastic declines in numbers and reductions in distribution, but no species has become extinct because of direct human exploitation. However, overexploitation combined with severe habitat loss have brought several species to the brink of extinction.
Crocodilians of all species depend upon wetland habitats. Different species have varying preferences and requirements and crocodilians have adapted to most available tropical and subtropical wetland types (marshes, mangroves, rivers, lakes, lagoons etc.). Because they are quite large animals and because crocodiles increase through several orders of magnitude of size as they grow from hatchling to adult, they require areas of habitat that are both large and diverse. A few species are adaptable and are able to persist in small areas of disturbed habitat, for example the common caiman and Chinese alligator. However, most species require relatively large areas (hundreds of square kilometers) of undisturbed wetland to maintain large populations.
Habitat destruction has taken many forms. The most obvious destruction of wetlands is by drainage and infilling, deforestation, conversion to agricultural use and pollution. However, more subtle habitat alteration may also be disastrous for crocodiles. In the Andaman Islands the saltwater crocodile is dependent upon restricted areas of fresh water marsh for successful nesting. Unfortunately these areas are increasingly used for human agriculture and crocodiles attempting to nest in them are killed. Therefore, while large areas of pristine riverine and mangrove habitat remains, the population is in decline. In the Philippines, people live along the rivers and use them extensively for fishing and transport. While the riverine habitat appears intact, and many areas have relatively low human densities, the constant attrition of crocodiles killed by people and caught in nets has caused the virtual disappearance of two species, the Philippine and saltwater crocodiles. Rural people are often intolerant of large and potentially dangerous crocodiles and the deliberate destruction of both nests and adults is widely reported (e.g. Madagascar, Andamans, China, Bangladesh). The creation of dams and impoundments has an ambiguous effect. Initially, the original complex, well vegetated marshy habitats may be replaced by simpler reservoir lakes with bare shores and crocodile populations may decline. New impoundments are often highly productive and support crocodile populations (e.g. Lake Argyle, Western Australia, Lake Kariba, Zimbabwe), but fluctuations in water level due to agricultural or hydroelectric demand has affected reproduction of crocodiles in impoundments in Honduras, India, and Zimbabwe. The effect of humans on crocodile habitat may also be indirect and distant, such as the contamination with mercury and pesticides in Florida. This is suspected to inhibit crocodilian reproduction. In general, crocodilian populations become threatened in direct proportion to the proximity and density of human populations. At the same time, most species of crocodilian are relatively adaptable and ecologically robust. If their minimal requirements for prey, suitable thermal conditions and nesting habitat can be maintained then they can often persist in habitats that are modified by people. However, crocodile mortality by people, both deliberate and inadvertent, must be controlled.
Conservation of crocodilian populations is therefore highly dependent upon providing incentives to maintain crocodiles and their habitats in a relatively undisturbed state, and a willingness to accept management practices that allow crocodiles and humans to co-exist.
Skinning farm raised alligators, Alligator mississippiensis.
This tightly regulated program produces over 100,000 legal
skins annually and provides in excess of US$ 1 million to
support conservation, management and research on this
species. Photo by F.W. King.
Conservation strategies for crocodilians
Since about 1970, after recognition that the uncontrolled exploitation of earlier decades had caused serious declines, many species have benefited immensely from the institution of improved protection and tightly controlled exploitation. However, crocodiles pose some difficult problems for conservationists. The larger species in particular are usually regarded as dangerous and unattractive by the people who have to live near them. When conservation programs have succeeded and crocodile populations have grown, problems of crocodile-human conflict often increase. Some species continue to require complete protection in protected areas and preservation in captivity. However, the majority of the species require a more creative approach that provides incentives to people living with crocodiles to offset their real and perceived costs.
Sustainable use has become a key element in the conservation of crocodilian species (Thorbjarnarson 1992, Jenkins 1993). An activity is sustainable if it can be continued indefinitely (IUCN/UNEP/WWF1991). Sustainable use is complex because we must consider both the effects on the target population (e.g. caiman that we wish to hunt) and the effects on non-target species and the associated ecosystem (e.g. hunting caiman may affect wetland nutrient cycles and fish populations). In many cases, it is difficult to prove that use is sustainable, but it is relatively easy to recognize when use is not sustainable. If people use any resource at a rate that exceeds the ability of the resource to replace itself, then the resource will become depleted.
Saltwater crocodile, Crocodylus porosus, and New Guinea
crocodile, Crocodylus novaeguineae, in a ranch in Irian
Jaya, Indonesia. Photo by G. J. W. Webb
The challenge for researchers and managers responsible for crocodilians is to establish programs where there is high probability that use is sustainable, which can only occur if the resource and habitats are conserved.
Sustainable use of crocodilians can provide the necessary economic incentives to encourage people to maintain crocodilians and their habitats in a natural state. A general model has emerged for the successful sustainable use of crocodilians based on experience of nearly 20 years in such diverse countries as Papua New Guinea (Genolagani and Wilmot 1990), Venezuela (Quero de Peρa 1993), Zimbabwe (Hutton and Child 1989), USA (Joanen et al. 1990) and Australia (Webb et al. 1992). While each of these countries uses a different management scheme, there are elements of similarity. In each of these examples crocodilian populations have increased or remained stable in the wild while supporting economically viable levels of exploitation. This is surely the ultimate test of sustainability although it remains to be seen if these systems remain stable for longer time periods.
Crocodile eggs are carefully packed for transport to a
central incubator facility at the ranch. In Papua New
Guinea, hen eggs and a cash price are paid to local
villagers who protect nesting females as a valuable
resource. Photo by B. Vernon.
The basic components for crocodilian sustainable use demonstrated by these programs are the following:
2. Recovery: Where necessary and indicated by the survey, exploitation was preceded by a period of complete protection. This allowed crocodile populations to increase in size and management agencies to develop expertise and infrastructure. Crocodilians have a life history strategy that enables them to recover from low population levels quite rapidly (510 years), as long as their habitats remain intact.
3. Monitoring: Based upon the same standardized techniques, a regime of periodic monitoring of the population was undertaken. Changes in the rate of exploitation were based upon the results of this monitoring program. It is noteworthy that neither survey or monitoring need generate an absolute estimate of the number of crocodilians present, as long as a reliable index of the trend (increasing or decreasing) is obtained.
4. Biology: Exploitation of the crocodilian population was structured to focus harvest on those life stages where high mortality has the least affect on the population. This was usually the eggs and hatchlings, and adult males. Determination of which parts of a population to exploit, and how much, were derived from biological studies. The similarity of life style of different species of crocodilians has allowed the broad extrapolation of results on a few species to others with only superficial corroborating studies. It was not necessary to exhaustively study each species.
5. Caution: Levels of exploitation were kept well below the calculated levels that the population may be able to sustain. This was accomplished by implementing closed seasons, size limits, gear limitations, restricted licensing of processors and traders, harvest and export quotas, and often by the intrinsic inaccessibility of some parts of the crocodile populations range. In this way, natural environmental fluctuations and unexpected catastrophes can still be absorbed by the population.
6. Local benefit: The immediate economic benefits, and the responsibility for management were vested in the social groups closest to the extraction phase of exploitation. In Papua New Guinea these were tribal land owners, in Venezuela ranchers, in Australia and USA local businessmen and farmers.
7. Enforcement: Despite optimistic expectations that enlightened self interest would ensure good compliance with regulations, an effective enforcement mechanism was necessary to ensure compliance. This extended to harvest, trading, tanning, manufacturing and export controls.
8. Trade control: Because the main economic benefit of crocodile use is derived from international commerce, a stringent system for controlling international trade was a primary mechanism for controlling use and ensuring sustainability.
9. Economic feedback: A proportion of the economic returns from use was retained and used to support monitoring, management and enforcement. This was usually in the form of license fees, export fees, and user access charges.
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| Dante Videz (left) and Andres Siejas (right) record field data on an American crocodile hatchling, Crocodylus acutus, in Venezuela. Photo by F.W. King. |
Nile crocodiles, Crocodylus niloticus, on a ranch in Zimbabwe. Ranching of eggs taken from the wild gives an incentive to conserve wild populations and their habitats. Photo by P. Ross. |
Crocodilians can be used sustainably by several methods; hunting of wild crocodilians, ranching (i.e. bringing eggs or hatchlings from the wild and raising them in captivity) and captive breeding (farming) by maintaining breeding adults in captivity and raising their offspring. Each of these has advantages and disadvantages in terms of conservation value, ease of regulation, and economic costs and returns (David 1994). Sustainability is possible, and demonstrated, for each method and many successful national crcocodilian management systems utilize a combination of methods. Understanding the relative advantages and problems of the different methods is crucial to making sustainable use likely.
Applications of these measures are described in David (1994). The two key elements of this system are that (i) monitoring allows a prompt response (by changing use levels) to any perceived downward trend in abundance or population structure indicating overexploitation and, (ii) that the people who might be tempted to overexploit the population have the greatest vested interest in maintaining it. The real breakthrough for crocodilians has been the success of the Crocodile Specialist Group in convincing the large international traders and manufacturers of crocodilian products that they can successfully do business with equal or enhanced profits if sustainable use schemes are in place. The support of the commercial sector has provided powerful leverage to encourage compliance by producing countries and has been an incentive to invest in good sustainable crocodilian management.
Skinning saltwater crocodiles during a government
demonstration and training course for villagers on the
Sepik River, Papua New Guinea. Size limits control harvest
of wild crocodiles in Papua New Guinea. Photo by D. Jelden.
This link between commerce and conservation has some perils. Between 1990 and 1993, the price of all crocodilian skins on the international market was dramatically reduced (Woodward et al. 1993). The cause of the crash was complex, involving worldwide economic trends and overproduction of skins in farms beyond the market demand. Concerns were expressed that the sudden removal of economic incentives for conservation would undermine the CSG sustainable use strategy. Great hardship was experienced in the commercial sector. Some operators withdrew from the industry and most management programs based on sustainable use saw a reduction in their budgets. However, an anticipated upswing in illegal, unsustainable production of crocodile skins did not occur. The combination of national and international regulations and the long term interest of producers and traders served to maintain and considerably strengthen the regulatory system. We take this as strong evidence that the application of sustainable use strategies to crocodilian conservation is based on a firm foundation and is sufficiently robust to withstand occasional economic setbacks.
There remains a group of crocodilian species that, because of their current status or undesirable quality of their products, are unlikely to benefit from sustainable use. The CSG remains strongly committed to the application of more traditional conservation practice such as habitat protection and captive breeding for such species. We also recognize that the individual characteristics of different countries make some techniques more feasible and effective than others. The species accounts detail many of these programs and the CSG remains committed to our basic goal of crocodilian conservation.
Saltwater crocodile, Crocodylus porosus, hatchling,
Northern Territory, Australia. Successful incubation of
crocodile eggs from the wild is the basis of ranching
programs. Photo by G. J. W. Webb.
In the period 19921994, IUCN and CITES both revised
and clarified the criteria by which species were evaluated
for conservation status. Previous categories used in both
the IUCN Red Lists and in the CITES Appendices were
seen to be vague and sometimes arbitrary. Although they
had served well for many years it was deemed advisable to
develop new categories, defined by criteria that were
objective (i.e. measurable and quantitative), simple,
universal (i.e. broadly applicable to all or most taxa) and
flexible. The revised criteria have been developed based
upon an understanding of population dynamics and how
these affect the probability of a species becoming extinct in
a given period of time (Mace and Lande 1991, Mace et al.
1992). Four fundamental foundations of species biology
are recognized:
1. Rate of population reduction
2. Extent and fragmentation of occupancy or range
3. Effective population number (number of breeding
adults)
4. Life history structure
In simple terms, species that remain numerous and widespread and have no specially limiting features of life history are considered to be unlikely to become extinct in an immediate (110 years) or ecological (10100 years) time frame. Species which show a sharp reduction in one or more of these, or which have specially limiting life histories (e.g. extremely long periods to reach maturity, special habitat requirements) are more likely to become extinct. After extensive discussion and numerous revisions a series of criteria based on these fundamentals have evolved. Some debate remains on the extent to which the criteria are truly objective and meet conservation needs but for the present the revised categories, known as the IUCN Red List Categories (IUCN 1994), provide a valuable and improved method for evaluating species status. Full details of these new categories are described in Appendix 2 of this Action Plan. Table 2 provides an overview of the extent to which survey data are available for the species of crocodilians. The species accounts of this revised Action Plan include an evaluation of each species using the new criteria (Table 3).
These analyses confirm our earlier evaluation of which crocodilian species warrant priority conservation action, but reassesses which countries need priority action. Two additional species Crocodylus cataphractus and C. moreletii are noted as being unlikely to be seriously endangered at present, but are a priority for information gathering to allow adequate status assessment. Combining these evaluations produces a new set of priorities which are presented in Table 4.
Orinoco crocodile, Crocodylus intermedius, raised in
captivity and released as part of a population restocking
program in Venezuela. Photo by C. Lageaux.
In the species accounts which follow we have analyzed the present status and state of knowledge of the crocodilian species, identified countries in which the needs are most urgent, and specified the highest priority projects. By combining these factors, it is possible to rank projects and identify the most immediate priorities. Ranking is always problematic, in part because different criteria of urgency may conflict, and in part because favored or politically desirable projects may not appear in the rank order where we would most like to see them. There is also a degree of arbitrariness in assigning more concern to one species over another. However, in the present analysis, the species rankings are based on our best evaluation of the severity of current threats (Table 3).
The following ranking should therefore be accepted only provisionally as a general guide to what is really urgent and what might be safely delayed without increasing the likelihood of extinction of a crocodilian species.
Analysis of high priority projects for high priority species, endangered species and vulnerable species yields a concise list of 35 key projects. Of these, five are substantially in progress, with funding and personnel assigned and activities underway. Thirteen could be considered as in the early stages of initiation, proposals are written, preliminary field studies have been carried out, initial contacts in target countries are well established. The remaining seventeen are projects that have yet to be initiated and indicate a clear direction for future activities.
Projects should not be considered for funding or implementation in strict order of rank, but all things being equal, a higher ranked project should be considered with favor over a lower ranked project. As all things are rarely equal, we expect that other factors, including available funds, available expertise, preferences and priorities of funding agencies, political stability, probability of success, available time and other similar factors will continue to influence project funding and implementation. Notwithstanding such considerations, some clear priority ranking emerges from this analysis that could usefully guide project development.
To assign priorities the following considerations were
applied in order of importance:
Species of highest priority (Tables 3 and 4).
Countries of highest priority (Table 4 and accounts).
Projects of highest priority (accounts).
Projects to immediately avert extinction.
Projects involving several countries.
Projects to implement management and conservation.
Projects to ascertain status.
Basic biology and research.
Moderate priority projects.
More complete descriptions of each project are given following each species account on the indicated pages.
A1. Alligator sinensis, China, avert extinction, enhanced
protection and continued monitoring of wild
populations (initiated).
A2. Alligator sinensis, multinational. China, USA,
Thailand, management and coordination of captive
populations.
B1. Crocodylus mindorensis, Philippines, development of a
national crocodile conservation program (initiated).
B2. Crocodylus mindorensis, multinational. Philippines,
USA, Australia, coordination of captive breeding
program (in progress).
C1. Tomistoma schlegelii, Malaysia, status surveys in
Sarawak and Malaysia (initiated).
C2. Tomistoma schlegelii, Indonesia, implementation of
conservation programs (initiated).
C3. Tomistoma schlegelii, Indonesia, status survey
Kalimantan and Sumatra (in progress 1996).
D1. Crocodylus siamensis, Thailand, extinction prevention,
protection of habitat and restocking (initiated).
D2. Crocodylus siamensis, Cambodia, status survey and
conservation and management plan development.
D3. Crocodylus siamensis, Vietnam, status survey and
conservation and management plan development.
D4. Crocodylus siamensis, Laos, status survey and
conservation and management plan development.
D5. Crocodylus siamensis, Indonesia, verification of
distribution and protection in Kalimantan (initiated).
E1. Crocodylus intermedius, Colombia, survey of
population status (initiated).
E2. Crocodylus intermedius, Venezuela, conservation in
Cinaruco-Capanaparo National Park (in progress).
E3. Crocodylus intermedius, Venezuela, monitoring of
restocked populations (in progress).
F1. Crocodylus rhombifer, Cuba, prevent extinction,
protection of the Zapata Swamp (initiated).
F2. Crocodylus rhombifer, Cuba, management and
conservation, re-establishment of additional wild
populations (in progress).
F3. Crocodylus rhombifer, Cuba, survey of the Lanier
Swamp (in progress).
G1. Gavialis gangeticus, India, national management plan
for crocodiles (initiated).
G2. Gavialis gangeticus, binational. India, Nepal,
coordination of gharial management and conservation
(initiated).
G3. Gavialis gangeticus, Pakistan, status survey and
development of captive rearing.
H1. Crocodylus cataphractus, multinational. Congo, Dem.
Rep. Congo, Nigeria, Gabon, Central African
Republic, status surveys.
I1. Melanosuchus niger, multinational. Brazil, Colombia,
Ecuador, Guyana, French Guiana, Peru, status
surveys.
I2. Melanosuchus niger, Brazil, implementation of
conservation and management program.
I3 Melanosuchus niger, Colombia, implementation of
conservation and management program.
I4. Melanosuchus niger, Brazil, basic ecological studies
(initiated).
J1. Crocodylus acutus, Cuba, management and protection
program (in progress).
J2. Crocodylus acutus, Belize, management and protection
program.
J3. Crocodylus acutus, Colombia, status and distribution.
J4. Crocodylus acutus, multinational. Mexico, Costa Rica,
Panama, Jamaica, status surveys and conservation and
management program.
K1. Crocodylus palustris, Pakistan, prevent extinction,
survey as a base for conservation and management
program.
K2. Crocodylus palustris, Sri Lanka, prevent extinction,
survey as a base for conservation and management
program.
L1. Osteolaemus tetraspis, multinational. Congo, Dem. Rep.
Congo, Gabon, Nigeria, Central African Republic,
surveys and local use assessment, see H1. above.
M1. Crocodylus moreletii, Mexico, status surveys and
development of conservation and management
programs (initiated).
M2. Crocodylus moreletii, Guatemala, status surveys and
development of conservation and management
programs.
N1. Crocodylus siamensis, Crocodylus mindorensis,
Crocodylus novaeguineae, Taxonomic clarification of
the complex.
N2. Crocodylus palustris, Iran, conservation.
N3. Crocodylus porosus, Sri Lanka, survey and conservation.
The species accounts also list additional projects with
the suggested rank order of:
Moderate priority projects for high priority species.
Moderate priority projects for Endangered species.
Moderate priority projects for Vulnerable species.
All projects for Lower Risk species.
Technicians weigh an Australian freshwater
crocodile, Crocodylus johnsoni, at McKinley
River, Northern Territory, Australia. Photo
by G.J.W. Webb.