Does Mortality Impact Negatively on Hippopotamus (Hippopotamus amphibius) Population Size and Density in Luangwa River, Zambia? A Historic Perspective

Abstract

Influence of mortality on hippopotamus (Hippopotamus amphibius) population size and density in the Luangwa River, Zambia was assessed. Mortality factors considered were culling, trophy hunting, control, disease (anthrax), poaching and natural mortality. Number of hippos killed were collected from Zambia Wildlife Authority (ZAWA) records, Department of Veterinary and Livestock Services (DVLD) and field observations during this study. Analysis of data showed that hippos killed through different forms of mortality were 2,674 (mean 429) varying significantly from year to year, being higher in some years and lower in others. Hippos killed by each of the six mortality factors also varied significantly, with some mortality factors killing more hippos than others. Student New Man's -Keuls Test (SNK) showed that a combination of culling and disease killed more hippos (95 %) than the other four mortality factors combined. Culling killed (63 percent), disease (32 percent) and the remaining four (4) mortality factors killed only 5 percent. However, the number of hippos killed through all six mortality factors combined was still too low and insignificant to negatively impact on hippopotamus population density over the same period. Population density appeared not to be negatively affected by mortality as density did not fluctuate significantly in response to the number of animals dying. It was concluded that mortality was not an important factor in reducing the Luangwa hippopotamus population density. More studies are required to identify key factors affecting population density.