Notes and records

The abundance of Hippopotamus amphibius inthe Black Volta River at Bui National Park,Ghana.

Daniel Bennett1, Nicky Green2 and Brian Basuglo31Department of Zoology, University of Aberdeen,

Tillydrone Avenue, Aberdeen, AB24 2TZ, UK, 27 The

Banks, Bingham, NG13 8BL, UK, 3Ghana Wildlife

Department, Box M.239, Accra, Ghana

Introduction

The hippo (Hippopotamus amphibius Linn.) is consideredby the IUCN to be widespread and secure (Eltringham,1993). However, populations inWest Africa have beenin decline for at least100 years and only 7000 animalsare estimated to be left in the region, compared with150,000 animals in Eastern and Southern Africa. InGhana, the hippo is classed as endangered and isa¡orded complete protection under national law. It wasonce widespread throughout the Volta system but theonly surviving animals are found in the Black VoltaRiver from Bui National Park upstream to the borderwith Burkina Faso. Within this area, two populationshave been identi¢ed, one within Bui National Park andanother around Wichan, near Wa in the north of thecountry (Choribe, pers. comm.). Neither population iswell de¢ned and only in the former area is the hippos'habitat a¡orded protection. According to Eltringham(1999) hippos are also found in Mole and DigyaNational Parks in Ghana, but there is only a single ani-mal at the former site, and none at the latter (B. Basuglo,pers. obs.).

Materials and methods

The aim of this study was to make an estimate of thehippopotamus population the southern portion of Bui

National Park, from Batoo village (8�170N/2�160W)upstreamas far as Bope (8�220N/2�190W).The workwasconducted by members of the Aberdeen UniversityBlackVolta Expedition between June and July 1997. Forthe purposes of the study the river was divided into ¢vesections (coordinates given inTable1). Traditional localcanoes were used for the survey, each containing twolocal ¢shermen and two researchers. Areas of the riverwere surveyed daily (except Sundays) throughout July.Estimates were made by recording numbers of headsvisible every15 s over at least 5 min, and using the max-imum value obtained. Fishermen's estimates of totalnumbers were usually higher than those of theresearchers, but the lower value was used. Animalsseen were classed as neonates or others. Neonates wereeasy to identify by their very small size. In addition,some groups were counted from the riverbank duringother work.

Results and discussion

In total, 31 hippo sightings were made, 23 from theriver and eight from the riverbank. Hippos were mostcommonly seen in groups of 1^9 animals (mean 5,standard deviation 2.7, median 5, interquartile range3^7.8). All groups of four or more hippos includedbabies. Mean proportion of juveniles in these groupswas 0.22 (SD � 0.06, range 0.13^0.33) Aggregationswere most common around the outlets of tributarysteams, but we could ¢nd no evidence that hippos everenter these tributaries, probably because they are pre-vented from doing so by dense vegetation. Outlets of tri-butaries therefore provide good vantage points fromwhich to estimate hippo numbers during riverbankcounts.The maximum estimate is derived from riverbank

sightings on 24 July, when ¢fteen individuals were seenat the same time. However, this is likely to be an under-estimate of total numbers, because the hippos seen onthis occasion probably represent two groups from theCorrespondence: Daniel Bennett, E-mail: d.bennett@abdn.ac.uk

# 2000 East AfricanWild Life Society, Afr. J. Ecol.,38, 372^373372

northern sectors of the study area. Another group ofat least nine animals occupied sectors A & B and occa-sionally strayed towards Batoo Village. The length ofriver sections (estimated from a 1: 50,000 map) aver-aged 2.3 km (SD � 0.47, range 1.8^3.0). Using meannumber of hippos seen per section of the river (Table1)a mean density of 2.11 (þ 0.17) hippos per km of river issuggested.It was not possible to identify individuals with cer-

tainty. Attempts at identi¢cation using the mirror tech-nique described by Karstad & Hudson. (1984) andNorton (1988) were not successful. Assuming thathippo densities throughout the park were at least ashigh as those recorded by us in the southern sector, thehippo population at Bui seems to be secure, in the shortterm at least, and, based on the high incidence of juve-nile animals, numbers may be increasing. However,compared to hippopotamus populations surveyed ineastern Africa, the numbers of hippos in the BlackVoltais very small (Eltringham, 1999). Outside the NationalPark, virtually all riverbank habitat has been convertedto agricultural use. An increase in hippo density at Buimay have the e¡ect of displacing individuals across thesouthern park boundary and thus increasing the num-

ber of encounters between humans and hippos, whichis clearly undesirable.

Acknowledgements

Thanks to G.A. Punguse, N.K. Ankudey, B.A. OforiFrimpong and M. Komoah of the GhanaWildlife Depart-ment, and to all members and sponsors of AberdeenUniversity BlackVolta Expedition.

References

ELTRINGHAM, S.K. (1993).The common hippopotamus(Hippopotamus amphibius). In: Pigs, Peccaries and Hippos. StatusSurvey and Conservation Plan (Ed.W.L.R. OLIVER). IUCN, Gland,Switzerland.

ELTRINGHAM, S.K. (1999).The Hippos.Academic Press. London.KARSTAD, E.L. & HUDSON R.J. (1984) Census of the Mara Riverhippopotamus (Hippopotamus amphibius), southwest Kenya.1980^82. Afr. J. Ecol. 22,143^147.

NORTON, P.M. (1988) Hippopotamus numbers in the LuangwaValley, Zambia, in1981. Afr. J. Ecol. 26, 337^339.

(Manuscript accepted15March 2000)

Table1 Abundance of hippos in studyareas

Area A Area B Area C Area D Area E

Length (km) 1.8 3.0 2.0 2.3 2.5Mean no. hippos seen 4 6.5 4 5 4.7Standard deviation 4.24 1.52 1.41 2.62 4.03Hippos per km 2.29 2.17 2.0 2.22 1.88Coordinates of studyareas:

Area A: 2�15.250N/8�17.150Wto 2�17.300N/8�16.000WArea B: 2�16.000N/8�17.300Wto 2�16.100N/8�18.400WArea C: 2�16.100N/8�18.400Wto 2�16.150N/8�19.200WArea D: 2�16.150N/8�19.200Wto 2�16.500N/8�20.250WArea E: 2�16.50'N/8�20.250Wto 2�17.250N/8�21.300W

# 2000 East AfricanWild Life Society, Afr. J. Ecol.,38, 372^373

373Abundance of Hippopotamus amphibius in the BlackVolta River