Crocodiles of the Zambezi
The Nile crocodile (Crocodylus niloticus) is the largest crocodile species on the African continent. Despite its long history of co-existence with humans, dating back from the ancient Egyptians who worshipped the crocodile-god Sobek for its powers of protection and fertility, these imposing predators have remained a reviled species in many parts of Africa, as a result of human-crocodile conflict.
This conflict arises particularly in the Zambezi heartland (an area spanning parts of Zambia, Zimbabwe and Mozambique through which the Zambezi river flows). This is where the Earthwatch project, Crocodiles of the Zambezi, is located.
As with most crocodilian species worldwide, the Nile crocodile is a top predator (one that has virtually no predators of its own and occupies a top position in the food chain) and as such, plays a crucial ecological role in the aquatic ecosystem in which it lives. Nile crocodiles feed on fish and aquatic species, naturally controlling the populations of predatory species such as barbell catfish, so that these do not deplete the numbers of other fish further down the food chain that may be of commercial value, or provide an important source of food for other species. The crocodiles also keep river environments clean by consuming dead animals that would otherwise remain a source of pollution, which helps nutrient recycling. In this way, the Nile crocodile is a significant keystone species (having a disproportionate effect on its community relative to its abundance).
Lack of thorough scientific study, combined with a misunderstanding of this species, remains the biggest threat to Nile crocodiles. The development of crocodile ranching and the adoption of international trade regulations in Zambia, Zimbabwe and Mozambique, has saved the species from the brink of extinction after populations were severely depleted following a period of illegal hunting in the mid-20th century. However, there has been little effort so far to research Nile crocodile population dynamics and ecology, and to determine whether crocodile ranching practices are sustainable. This in turn has resulted in the absence of adequate management and monitoring plans for the species. Human-crocodile conflict has further complicated management of crocodiles in the Zambezi heartland as a result of competition for resources and periodic fatalities as a result of crocodile attacks.
Building on previous research in Botswana, the Crocodiles of the Zambezi project, led by Dr. Alison Leslie from the Stellenbosch University in South Africa and Dr. Richard Fergusson from Asante Sana (Zimbabwe), has embarked on the most intensive study of Nile crocodiles ever undertaken in the middle-Zambezi area. The project's aim is to record valuable ecological information on this keystone species that can be used to help formulate regional management plans and conservation strategies such as the Zambian National Policy for Crocodile Conservation and Management. The project has also liaised with stakeholders such as conservation authorities in Zambia and Zimbabwe, as well as crocodile ranchers in the Zambezi heartland, to increase scientific understanding of the population trends of Nile crocodiles and how these are affected by ranching.
With the help of Earthwatch volunteers, 111 crocodiles of various sizes were captured and processed during the 2007-2008 field season. Processing includes weighing, measuring, determining the individual's sex, and taking blood and urine samples that can be tested in the laboratory to ascertain the health status of crocodilian populations. Crocodiles were also marked to provide a means of estimating total population size when recapturing or re-sighting marked individuals in the future. In addition, three crocodiles were fitted with radio transmitters to gain an idea of their dispersal patterns and distribution range.
Nesting surveys (counting the number of nests in an area and recording their characteristics) form a key component of the research and are being conducted in cooperation with crocodile farmer associations, as well as with wildlife departments in Zambia and Zimbabwe. These surveys will determine habitat suitability for crocodiles, an essential factor informing the development of conservation strategies and the assessment of land use in the region.
The project has also resulted in educational achievements - especially important in the light of the human-crocodile conflict. The research team has established an educational programme and started to conduct regular visits to schools in the Zambezi valley. And a partnership with the Wildtracks Lodge in Zambia has provided good facilities for running educational programmes for schools focused on crocodile ecology. The researchers have also visited tourist lodges on both sides of the Zambezi River to inform lodge owners and staff about the project.
Increasing research into the ecological and physiological requirements of the species is critical to understanding how crocodiles function in their natural environments. Monitoring efforts across the Zambezi heartland countries have been sparse or non-existent, apart from the annual collection of eggs by the ranching industry. Although these research efforts need to be harmonised to conform to more rigorous scientific standards, comparing data from recent years has indicated a decline in nest and egg numbers. Educational efforts and improved management are desperately needed to ensure that ranching is carried out in a sustainable manner, and to mitigate human-crocodile conflict, making Dr. Leslie's work all the more imperative.
Report by Nina Raasakka.
Find out more
Be a part of the research. Join the Earthwatch expedition Crocodiles of the Zambezi.
Read more in this feature about Conservation on the Zambezi, and find out more about the Nile crocodile.