Population dynamics and human crocodile conflict of the Nile crocodile, Crocodylus niloticus, in the lower Zambezi valley

Abstract

The lower Zambezi valley is an important conservation area for both Zambia and Zimbabwe, encompassing areas of varying levels of habitat and wildlife protection. Crocodiles have an important role in the ecosystem a well as a significant economic value, both attributes require careful management to ensure their preservation. This study investigated depredation of crocodile nests and estimated the population with a view to parameterising models which could be used to simulate harvesting strategies. Combined with a social survey the results are discussed in terms of enlightened crocodile management. The methodology encompassed four main areas: 1) An artificial crocodile nest experiment to ascertain levels of depredation at the egg stage. 2) Crocodile population surveys to estimate the abundance and size structure. 3) Deterministic stage-based and integral projection models compare observed to predicted population structure and the influence of harvesting regimes. 4) A questionnaire survey to determine the scale of human crocodile conflict and the associated issues. The local habitat characteristics of simulated crocodile nests correlated with depredation probability and time to nest death. The crocodile population shows evidence of increasing but differed from the predicted model stage structure, indicative of a population not yet at equilibrium. Crocodile density increased in areas that had higher levels of wildlife/habitat protection. An integral projection model indicated the complex inter-relationships between population biology parameters. Perturbations affecting the smallest as well as breeding size crocodiles may cause a significant impact to lambda and fertility selection. The current human crocodile conflict mitigation is minimal and ineffective. Canoe fishing is the highest risk activity followed by collecting water. The most popular mitigation suggestions were additional water access points in villages and for selective or total removal of crocodiles. An underlying dislike of crocodiles by the local populace needs to be addressed in order for successful long-term conservation.