Since the year (2019) began, I have had an opportunity to have two field
excursions on Lake Edward, obtaining samples of fish and characterizing
the physical habitat and water conditions. As usual, this involves moving to
predetermined sites, and with the help of a collection of tools such as
gillnets, echosounders, GPS and others, we obtain the different data types.
During the excursions on this lake however, there are many things to take
of, and key among these are wild animals.
Lake Edward is located in Queen Elizabeth National Park, a distinguished
park that is actually a biosphere reserve. Several animal species that call it
home include elephants, loins, buffaloes, and many others including
threatened species. You may think that these animals have nothing to do
with somebody working in water because they are found on land but in
water you find hippos and the dangerous man eaters, the crocodiles. So,
you do not only care not to disturb the peace of the animals on land by for
example reckless hooting when driving but you do not have to mess with
them as contact with most of these animals can be fatal. Elephants kill and
do hippos, buffaloes and off course crocodiles and lions. The list is endless.
Off course my main interest is in what is in the water although recently you
must have been seem my article on elephants. Please revisit it here, it is
enriching. The excursions were wonderful. We caught many fishes, people
were engaged, we distributed some to locals for food (off course after
getting data and adequate collections) and personally, I encountered fish
species such as Labeo forskalii which I had never encountered (see pictures
below). Field work is always interesting. A part from the “fishy” things, the
highlights of the excursions were hippos and crocodiles. These frightening
creatures overlapped with our fishing grounds. Let me focus on crocodiles
Crocodiles seem to be many in this lake and if you fear a lot like me, you
may end up stopping at the lake shores especially if it your first time.
Indeed, I am thankful to fearless field assistants. Crocodiles are so abundant
that one was captured in our gill-nets and sometimes we retrieved fish
specimens partially eaten by crocodiles. May be some fish in our nets were
swallowed completely, who knows. Questions started coming up in my
mind wondering for example the importance of fish in the diet of
crocodiles, the susceptibility of fishers to crocodile attacks, whether you can
be attacked when you are on a boat, and the origins (whether native or
introduced) of the crocodiles. The following are some lessons learned.
The per capita dependence of crocodiles on fish is apparently small (Cott,
1961). I think their predation on fish may be a concern if populations are
high in a specific area or if threatened or endemic species are included in
their diet. The crocodiles in the area are a menace to local people. They kill
to an extent that local politicians have picked interest. The national agency
that takes care of Ugandan national parks (Uganda Wildlife Authority) has
responded to the outcry by relocating some crocodiles to crater lakes
deeper into the park and establishing protective cages on domestic
extraction points. People are also urged to take care and avoid them. These
measures seem not to work as people are still dying. It appears that you can
be attacked even you are in a boat because fishers have not been spared.
The biggest lesson to me was that crocodiles are not supposed to be in the
Lake Edward System which includes Kazinga channel and lakes Edward
The first account of the absence of crocodiles in the above system which I
came across is by Worthington (1932). He presents some notes on the
distribution of crocodiles in Uganda, noting its absence here and presence
in other water bodies including lakes Victoria, Albert Kyoga, Kwania, River
Nile, River Semliki (below the falls). Reports published later in 1960s
including (1969) have no reference to the presence of crocodiles in the lake
Edward-George system. The reasons given for the absence of crocodiles in
this system yet they are found in the neighboring Lake Albert System is
because of a probable barrier of Semliki falls and extirpation of earlier
extant populations by extreme environmental change. The later hypothesis
is supported by presence of fossils of crocodiles in sediments under the
Lake Edward system. This thinking also explains the absence, in this system
of some fish taxa such as Lates and Hydrocynus that are present in the
Albert system. The former hypothesis presents Semliki falls as a barrier that
halted the re-colonization of crocodiles through Semliki river just as it does
for fish flocks either side (Witte et al. 2009).
Jim (2009) and Spawls (2018) reported presence of crocodiles in Kazinga
Chanel and lakes George and Edward but wondered what could have been
their origin. Like they wondered, I am also wondering how they came
there. Was it a deliberate or undeliberate introduction, did the Semliki falls
falter in their function or the fossils resurrected? The first three reasons are
possible and regrettable. Worthington (1932) noted that re-colonization
through Semliki would be possible if the fringes of the river and the falls
were deforested. This is likely to have happened in recent times. This can be
excluded by undertaking a small study tracking movement of crocodiles
upstream Semliki beyond the falls. If this was not the means, a question
remains on who introduced it and for what. The presence of the species
there is regrettable because in most cases new introductions become
invasive and who knows, the species may already be or about to be
Cott, H.B. 1961. Scientific results of an inquiry into the ecology and economic status of the Nile Crocodile (Grocodilus niloticus) in Uganda and Northern Rhodesia. The Transactions of the Zoological Society of London, 29(4), 211-356.
Jim. G. 2009. Nilotic Lakes of the Western Rift: In H.J. Dumont (ed.), The Nile: Origin, Environments, Limnology and Human Use, Springer Science + Business Media B.V.
Spawls, S. et al. 2018. Field Guide to East African Reptiles. Bloomsbury Publishing, pgs. 544.
Witte et al. 2009. Fish Fauna of the Nile: In H.J. Dumont (ed.), The Nile: Origin, Environments, Limnology and Human Use, Springer Science + Business Media B.V.
Worthington, E.B. 1932. A Report on the Fisheries of Uganda Investigated by the Cambridge Expedition to the East African Lakes, 1930-31. Zoological Laboratory, Cambridge.