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111
THE FEEDINC ECOLOGY OF TWO NILE CROCODILE FOPIJLATIONS
IN THE ZAMBEZI VALLEY - A PROJECT SUMMARY
Ian Games
P.O. Box U.A. 296
HARARE
ZIMBABWE
INTRODUCTION
This short paper is a summary of a p{oject on $e feeding ecology ofthe Nile crocodile in the
Zambezi valley in both Zimbabwe and Mozambique (Figure 1).
The primary objective of this study was to assess the effect of crocodiles on the fish populations
of Lake Kdiba. The lake supports boft a successful crocodile management scheme, based on
sustainable utilization, and a burgeoning a.tisanal or inshore fishery. There has been
considerablexpansion of the fishery since independence
1980 (Murphree et al. , I 989) and
consequently there is pressure to open up areas prcviously closed to fishing. Conflict between
fishermen ard crocodiles exists (Chimbuya and Hutton, 1988) with many of the problems
centering around competition for the resource. This study represents fte first aftempt to
estimate fish consumption by crocodiles {iom a natural system which may be more typical of
other places in Africa, as previous studies were combinations of data from several localities
(Cott, 1961) or from "atypical" populations (Graham, 1968; Hufton, 1984).
The crocodile is protected in Zimbabwe and all sample,s were taken from live animals which
were subsequently released. A commercial cropping progranme on Lake Cahora Bassa in
Mozambique allowed the collection of data and samples from a shot sample (Games et. al,
1989)
STIJDY AREAS
The Zambezi river rises in the highlands ofAngola and Zambia and flows for more than 2 500
km through six countries before reaching the Indian Ocean. Two giant artificial lakes have been
built on the river at Kariba and Calora Bassa (Figure 1).
Lake Kariba has an area of 5 364 km2 and a volume of 156.5 km3 at a mean operating level
of 485 m a.s.l. A succession of drought yea6 since 1980 has depressed the mean openting
level of the lake to 479 m a.s.l., where it remained throughout the study period. A study site
was chosen in the Ume estuary which is protected on one sideby the Matusadona National Park
(Figure 2) and is relatively undisturbed by egg collection activities. Lake Kariba is one ol the
more intensively studied lakes in Afiica and a large body of information on all aspects of its
limnology and ecology exists (e,g. Balon and Coche, 1974; Bowmaker, 1973; J.M. Hutton Pvt.
lsd., 1991, Marshall, 1984)
The lake supports both inshore and pelagic (kapenta) fisheries. They are different not only in
the habitat exploited, but also in capital input and yields. The kapenta fishery began in 1973
and in 1984 produced 10404 t, almost 1l times as much as the more primitive and undercapitalized
inshore fishery (Bourdillon, ?t. dl, 1985).