Abstract

This study assessed factors regulating the Luangwa (Zambia) hippo population within the carrying capacity band along the 165 km stretch of the Luangwa River, Eastern Zambia. Objectives of the study were to 1) establish whether the hippo population had reached and remained within the carrying capacity band in the last 32 years, and 2) determine the influence on population size and density distribution of grass biomass produced, mortality, non food resources (geomorphologic features) and levels of protection. Total river bank counts were made and global positioning system (GPS) locations of hippo schools recorded. Measurements from culled hippo carcasses were taken to determine sex and age classes. Kidney fat index (KFI) was used to determine body condition. Herbaceous growth was clipped and weighed to assess biomass. River geomorphologic features were taken by flying over the area in a light aircraft. Carrying capacity (K) was found to be 6,000 individuals at a density of 35 per km,oscillating within a carrying capacity band of 2,000 individuals in eight irregular cycles. At K,recruitment declined; calves and juveniles were 15% of the population and KFI was low at 40% by October. Grass biomass was high at 7, 850 kg/ha in 2008. Mortality did not disrupt population density. It was concluded that food was the main factor regulating hippo population size and density while geomorphologic features influenced the pattern of hippo population density distribution. Further research is required to establish primary production in ‘lean’ and ‘fat’ years and to monitor range trend condition as well as the impact of anthropogenic factors on the hippo population.

Key words: Carrying capacity, primary production, body condition, geomorphologic features.