Influence of river geomorphologic features on hippopotamus density distribution along the Luangwa River, Zambia

Abstract

River geomorphologic features along a 165-km stretch of the Luangwa River in eastern Zambia were assessed in 2008 to determine their influence on hippopotamus pattern of density distribution. A fixed high wing Cessna 206 aircraft fitted with geographical positioning system (GPS) was flown over the stretch taking coordinates for each geomorphologic feature, followed by taking length in metres of each geomorphologic feature on the ground. A total hippopotamus count was later carried out along the same stretch. Sixty-four geomorphologic features were recorded along the stretch of the river. Of the total geomorphologic features recorded, 34 (53%) were river bends, 13 (20%) lagoons and 17 (27%) were confluences. Hippo density was highest in river bends (75.48%), confluences (9.18%), lagoons 6.03% and all the other features put together had only 9.38%. It was concluded that geomorphologic features influenced hippopotamus pattern of density distribution in the Luangwa River.

Does the Luangwa Hippo Population Size and Density Distribution Vary between Upper and Lower Study Blocks? What Are the Management Implications of Such Distribution Pattern?

“…The number and nature of geomorphologic features (river bends, confluences and lagoons) was still 64 and had not changed since Chansa and others carried out a similar study [5] [6] reported in 2011. After food (grass biomass), geomorphologic features were the second most important factor in regulating hippo pattern of population density distribution between study blocks A-H along the 165 km stretch of the Luangwa River and not security.…”

“…A table showing study blocks, total number of geomorphologic features and their mean length and width measurements per study block and hippopotamus population density which was earlier presented by Chansa and others [5] was also verified. An F Test described by Dytham [11] and Fowler and others [12], was used to compare the means of population density between the upper and lower blocks.…”

“…Attwell [7] additionally reported having taken Darling to the Nsefu sector which he described as being the most densely populated sector of the Luangwa River in 1957, but said nothing about the lower study area. The Nsefu sector at the time had a population of about 100 animals distributed over 6.5 km (four miles) of river, and he further noted that Nsefu sector had numerous bends forming large flattened "S" shapes an aspect of which was later studied and reported in detail by Chansa and others [5]. The two studies, conducted by Attwell [7] and Darling [8] did not segment the upper and lower study blocks which for administrative purposes belong to two separate sector regimes.…”

“…Although Chansa and others [5] [6] suggested that geomorphologic features as factors determine the pattern of density distribution; they did not examine the distribution pattern between the upper and lower study areas since these are the recognized administrative segments used when conducting culling or trophy hunting. They attributed aggregated nature of distribution to geomorphologic features such as river meanders and confluences and primary production kg/ha [5] which in their view provided habitat welfare factors such as basking sites and food in varying quantities respectively. The factor of geomorphologic features was earlier mentioned by Attwell [7] and Darling [8].…”

Does shore length influence population size and density distribution of hippopotamus?

“…The hippopotamus retracted into lagoons and upper reaches and only returned to the main channel in the dry season. Attwell (1963) and Chansa et al (2011) also noted that areas with river meanders and extensive grasslands with palatable grass species such as Cynodon dactylon would carry high densities. Attwell (1963) further gave an example of the Lufupa River a tributary of the Kafue River particularly in respect of its upper reaches where the hippopotamus populations were higher than the main Kafue River on account of the slow water flow and increased amount of flood plain habitat with aquatic grasslands of the Busanga plains (Now a Ramsar Site) offering rich feed, particularly Echinocloa spp.…”