| Common names: Nile crocodile, Mamba (Swahili), Garwe
(Shona), Ngwenya (Ndebele)
Range: Angola, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Congo, Côte d’Ivoire, Dem. Rep. Congo, Egypt, Eritrea, Ethiopia, Equatorial Guinea, Gabon, Gambia, Ghana, Guinea, Guinea Bissau, Kenya, Liberia, Madagascar, Malawi, Mali, Mozambique, Mauritania, Namibia, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Somalia, South Africa, Sudan, Swaziland, Tanzania, Togo, Uganda, Zambia, Zimbabwe |
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Conservation overview
CITES: Appendix II in Botswana, Ethiopia, Kenya,
Malawi, Mozambique, South Africa, Tanzania,
Zambia and Zimbabwe (ranching criterion)
Appendix II in Madagascar, Uganda (annual quota
criterion)
Appendix I in all other countries
CSG Action Plan:
Availability of Survey Data – Variable, Adequate in
Southern Africa, but Poor or extremely poor elsewhere
Need for Wild Population Recovery – Moderate
Potential for Sustainable Management – Highest
1996 IUCN Red List: Not Listed (LRlc Lower Risk, least
concern, may be threatened in some parts of the range.)
Principal threats: Conflict with people.
Ecology and natural history
The Nile crocodile is among the largest and best known
biologically of all the crocodilians. Nile crocodiles are
widely distributed throughout sub-saharan Africa, and
historical records indicate its range formerly extended
into southern Israel and Jordan. The species was also
established on the Comoros Islands, and still exists on
Madagascar. As with all crocodilians, size among Nile
crocodiles is sexually dimorphic with the larger males
reaching lengths of up to 6m in exceptional cases. A large
volume of published information exists on topics such as
diet, thermoregulation, reproduction, social behavior,
habitat preference, and population dynamics. The first
modern monograph on the ecology of a crocodilian was
that of Cott (1961) on Nile crocodiles.
Nile crocodiles may be found in a wide variety of habitat types including large lakes, rivers, and freshwater swamps. In some areas they extend down into brackish water environments. Cott (1961) demonstrated that, as is generally true among crocodilians, there is an ontogenetic shift in diet, from insects and small aquatic invertebrates when young, to predominantly vertebrate prey among larger crocodiles. Hutton (1989) demonstrated differences in habitat utilization between juveniles, sub-adults and adults at Ngezi, Zimbabwe, and noted that animals entered a dispersal phase when approximately 1.2m long. Modha (1967) described some aspects of the social behavior, including the establishment of breeding hierarchies. Fergusson (1992) has recently studied the success of farm-raised crocodiles released to the wild.
Nesting is done in holes excavated in sandy banks during the annual dry season. Females become sexually mature when approximately 2.5m long, and lay an average of 45–50 eggs, although this varies considerably among populations. Incubation lasts 90–95 days, and the females open the nest and guard the young for a period after hatching. A model of Nile crocodile population growth and use is given by Craig (1992). The responses of the Zimbabwe population to prolonged sustainable harvest are also well studied (Loveridge and Hutton 1992, Taylor et al. 1992).
Conservation and status
In southern and eastern Africa a number of surveys for Nile crocodiles have been conducted in recent years, and information on crocodile status is good. Recent survey information is available for Tanzania (Games and Severre 1992), South Africa (Blake and Jacobsen 1992) and Kenya (Soorae 1994), while Hutton and Games (1992) provide a collection of recent surveys for Botswana, Kenya, Madagascar, Malawi, Mozambique, and Zambia conducted between 1981 and 1989. Most of this work has been part of a CITES sponsored initiative to implement sustainable management programs in countries that wish to harvest crocodiles. However, in central and western Africa very few survey data exist. For this region information on the status of Nile crocodile is provided by Behra (1987) for Gabon, Congo and the Central African Republic, and Waitkuwait (1988, 1989) for Côte d’Ivoire. The situation in Dem. Rep. Congo and Congo remains poorly known. Recent reports (e.g. Jones 1991) suggest that continued population declines in west Africa are largely due to habitat loss, although heavy extraction of skins in the 1970s has also contributed (Behra 1994c). For instance, Behra (1987) surveyed Gabon without seeing a single Nile crocodile. However, it is possible that Nile crocodiles in west Africa are found at naturally lower densities due to habitat factors and the presence of two other sympatric crocodilians. More survey and ecological studies in central and western Africa need to be undertaken to resolve this question. A remnant population was recently reported to be present at Matmâta in the Tagant Highlands of Mauritania (Behra 1994c). For the majority of African countries (25 out of 39), there is inadequate information on the status of Nile crocodile populations.
Although the status of the Nile crocodile is relatively
secure and abundant in southern and eastern Africa, in
western Africa it is greatly depleted. Among the 20 African
countries where we have some indication of the status of
C. niloticus, they are considered to be severely depleted in
six (30%), somewhat depleted in 12 (60%), and not depleted
in two countries (10%). Nile crocodiles have been extirpated
from three countries at the periphery of their range: Israel,
Algeria, and Comoros. However, the disappearance of
crocodiles from the former two countries may be partially
related to climate change and the resulting loss of wetland
habitats. A proposal to reintroduce Nile crocodiles to
Algeria is indefinitely postponed due to civil unrest (H.
Dumont, pers comm.). Crocodiles reported as extirpated
from the Seychelles are now shown to have been Crocodylus
porosus (Gerlach and Canning 1993) not Crocodylus
niloticus as previously thought.
As with all of the other large, commercially valuable species, hide hunting in the 1940s–1960s resulted in dramatic declines in population size throughout most of its range. However, protection given by national laws and international trading regulations have resulted in a recovery in many parts of the species range. As a whole, Nile crocodiles are not threatened, and locally large populations exist. Because of the species’ good status in southern and eastern Africa and the lack of information throughout most of west and central Africa, the Nile crocodile was given a “moderate” rating for the need for the recovery of wild population. In some areas human-crocodile conflicts have become a major problem, and is one of the driving forces behind the implementation of sustainable management programs. Serious problems of human mortality from crocodiles was reported from Tanzania (Jelden et al. 1994) and a special wild hunt quota of 1,000 was granted for 1995 and 1996 to address this problem (Anon. 1994b).
The Nile crocodile is one of the most commercially utilized species of crocodilians producing a “classic” hide. World trade numbered 80,000 skins annually in 1993 with the majority coming from Zimbabwe (54%) and South Africa (15%) from ranching and captive breeding (Collins 1995). Illegal trade is thought to be insignificant. In recent years the CITES Nile crocodile program has played an important role in developing sustainable yield programs, and has tried to emphasize ranching as the preferred means of obtaining conservation benefits from crocodile utilization. Zimbabwe, Botswana, Malawi, Mozambique and Zambia have long-standing ranching programs, permitted under the CITES ranching criteria (Res. Conf. 3.15), and no limitations on exports. Countries given quotas under Res. Conf. 5.21 were permitted to export cropped skins with the understanding that the future development of crocodile management programs will move towards ranching. This incentive appears to have worked and since 1990 five other countries (South Africa, Ethiopia, Kenya, Somalia, and Tanzania) have transferred to Appendix II ranching systems. Uganda and Madagascar retain CITES Appendix II under the quota system (Res. Conf. 5.21) and Sudan reverted to Appendix I status in 1994 following its failure to develop a successful ranching program. The direct cropping of crocodiles is discouraged under CITES ranching criteria, but still exists in Malawi, Tanzania and Mozambique. Cropping of crocodiles is still legal in other African nations (Sudan, Chad, Sierra Leone, Togo, Cameroon, Congo, Dem. Rep. Congo), but legal exports under CITES are not permitted.
No central or west and central African countries have implemented sustainable management programs as yet.
Priority projects
High priority
Surveys of wild crocodile populations in western and central Africa: Survey data are urgently needed for this region, not only for Nile crocodiles but also for the two other African crocodilians, Crocodylus cataphractus and Osteolaemus tetraspis. Country by country surveys of crocodile status and distribution are a prerequisite for developing conservation and management programs. Of particular interest are the major river systems and wetlands where substantial populations may remain e.g. the Congo-Ubangi system (Dem. Rep. Congo and Congo), Ogooe (Gabon), Niger-Benue (Nigeria), the Volta system (Ghana), and the Bahr Salamat-Chari system (Chad).
Moderate priority
Development and implementation of management programs for those countries planning sustainable utilization: A number of African nations are developing fledgling management programs based on sustainable harvesting. Population surveys and monitoring, training and program support are needed to foster these programs. A recent prioritization of countries to receive such support listed: Kenya, Tanzania, Sudan, Ethiopia, Somalia, and Congo (Hutton 1990).
Hutton (1990) outlines priority areas that need to be addressed for the development of sustainable use programs in these countries:
Nile crocodile, Crocodylus niloticus, Ume, Zimbabwe. Photo by P. Ross.