STUDY HIGHLIGHTS VULNERABILITY OF NILE CROCODILE
The Nile Crocodile (Crocodylus niloticus), an endangered species in South Africa, is the focus of a multi-faceted four-year research project led by Professor Colleen Downs from UKZN’s School of Biological and Conservation Sciences.
Initiated in 2009, the study will assess the spatial ecology, reproductive biology, habitat-use, population dynamics, ecotoxicology, nutritional ecology and genetic structure of the wild Nile Crocodile populations in the northeast region of southern Africa. The results will benefit national and international scientific and conservation management communities who are grappling with confirmed and suspected ‘die-offs’ of Crocodilian populations world-wide.
The concurrent research of four UKZN postgraduate students in the iSimangaliso Wetland Park (previously Greater St Lucia Wetland Park), the Ndumu Game Reserve and the Pongolapoort Dam is contributing to the Nile Crocodile Programme. The students have captured and taken blood and scute samples from the crocodiles, fitted them with telemeters and uniquely marked individual specimens with a sequence of three colour-coded plastic tags. This will enable the researchers to obtain valuable information on their movements and habitat-use each time they are re-sighted through aerial and ground surveys.
According to Professor Downs, “Crocodylus niloticus merit serious scientific study if the species and its wetland habitats are to be adequately protected and managed.” She explained that the Nile Crocodile, like all crocodilians, is considered an important biological indicator of the health of an aquatic ecosystem and that “mitigation of threats to crocodiles is useful for protection of aquatic habitats at an ecosystem level”.
The iSimangaliso Wetland Park and Lake St Lucia in particular, is a critical conservation area for wild crocodiles as it hosts the largest number of individuals in a single water body in South Africa. It is also probably the largest and most secure population in an estuarine environment throughout the species’ range.
Preliminary findings reveal a relatively positive scenario for the crocodiles at Pongalapoort Dam although poaching and rapidly changing water levels are of concern. Numbers at Lake Sibiya, however, are the lowest since the first aerial survey in 1987. Earlier studies indicate that this is linked to the increasing human population around the lake which in turn leads to an increase in demand for natural resources (e.g. water, food, building material) and conflict between people and crocodiles. At Lake St Lucia, due to the stressed condition of the ecosystem because of ongoing drought, the water levels are low and the number of large fish has diminished. This affects the older age classes of St Lucia crocodiles who rely mainly on a diet of fish and need to find fresh water supplies regularly. Blood and urine samples will reveal if the poor condition of the crocodiles is due to diet, disease or contaminants.
The Nile Crocodile Programme is indebted to Mazda Wildlife for vehicle support; the Hans Hoheisen Charitable Trust Grant for telemetry; the Bateleurs for assistance with aerial surveys; and Ezemvelo KZN Wildlife and the iSimangaliso Wetland Park for their support. Final results of the study will be published internationally, and, because of the global significance of the research, the data will be used to develop detailed management plans for the protection and long-term management of crocodile populations and aquatic ecosystems.