Estimation of fish abundance and catches in
littoral habitats of Kigoma Bay
Student: Huruma Mgana
Mentor: Peter McIntyre
Introduction
The pelagic fish community of Lake Tanganyika is composed of
large populations of six endemic species (Coulter, 1991). These
species have been the focus of most fisheries research on the
lake, including investigations of their ecology and interactions.
Much less attention has been paid to littoral fisheries.
The littoral zone can be defined as the area from 0-10m depth,
sub-littoral from 10-40m, and benthic zone extending down to
the oxycline (Coulter, 1991). Most of the fish diversity of the
lake is found exclusively in the littoral and sub-littoral zones.
Much of the lake’s diversity is species of the family Cichlidae,
but there are also many non-cichlid fishes as well (21 families;
Brichard, 1978).
Local fishermen normally fish by using gillnets, hooks, beach
seines, and a few other methods (Mabochi et al., 2000). There
are also companies which collect and sell ornamental fishes
found in littoral zone, which are caught while SCUBA diving.
This study aimed to investigate fishing pressure near Kigoma,
and assess the importance of the littoral fishery to the local
community.
Hypotheses
(1) The littoral fishery plays an important role in the well being
and life of fishermen.
(2) The fishermen’s catches reflect the relative abundance of
species.
(3) Fishemen have a stong influence on the littoral fishes.
Materials and Methods
Study sites
Fishermen were interviewed in their boats and at the main
landing sites around Kigoma bay: Kibirizi, Kigodeko,
Katabe Bay, and Katonga. Quadrat counts of littoral fish
were performed at all 12 limnology-team survey sites (see J.
Corman, this volume).
Partial counts
The most direct way of estimating absolute abundance is by
counting the number of individuals in well-defined areas (King,
1995). I conducted such counts while snorkeling during the
day over rocky habitats. This method has a low impact upon
the environment and is less labor-intensive than alternative
methods, and water clarity is suficient in Lake Tanganyika.
Negatively buoyant lines were used to establish three quadrats
(7x8 m) at a depth of 5m at each site. After a period of >30
minutes, two observers identified and counted all fishes within
the quadrats. Data were recorded on a pre-prepared list of
species written on an underwater slate.
Fishermen questionnaire
Gillnet and line fishermen were interviewed by means of
questionaires modified from (Kimaru and Msafiri, 2002; see
Appendix 1). Their catch was sorted by species, counted, and
weighed using a spring balance.
Results
A total of 41 fishermen were interviewed, including almost
all littoral fishermen operating in the Kigoma region. Most
fishermen used one of three methods : gillnets (36 fishermen),
hook and line (2 fishermen) and SCUBA (3 fishermen).
The average number of fish species caught per day was 5.7
species. The maximum number of fish species that were caught
was 15, although most fishers caught fewer than 7 species (Fig
1). The average fish catch during the survey was about 3.84
kgs, the maximum amount caught was more than 15 kgs which
was caught by few fishermen (Fig 2). The average number of
individual fishes caught per fisherman per day was 88, and the
maximum was 600. Most fishermen caught 20-40 individuals,
(Fig 3). Out of 41 fishermen, 38 claimed to be making a profit.
There was a strong correlation between the catch possessed by
each fisherman and the amount of money he claimed to make
(Fig 6).
Cichlids dominated the fishery, constituting 89% of the catch
(Fig. 4). Other contributing families included bagrid catfishes
(6.7%), Lates spp. (1.7%), and spiny eels (1.4%). All other
species were very rare. This roughly matched the results of
the littoral fish censuses. Cichlids constituted 97% of littoral
fishes (Fig. 7), and we recorded an average of 3.0 individual
fishes/m2.
Discussion
Littoral habitats of Kigoma Bay have both rock and sand
susbtrates, and are rich in flora and fauna. Cichlids species
are the dominant fish in the litoral zone, making it an attractive
fishing ground for fishermen. Our fishery survey indicated
that littoral fishermen rely primarily on gill nets, and harvested
an average of almost 4 kg (or 88 individuals) per day. Most
fishermen were fishing at greater depth than our littoral quadrat
Figure 1: Number of fish species caught per day per
fisherman. Arrow indicated the mean.
Acknowledgements
Figure 2: Biomass of fishes caught daily per fisherman.
Many thanks to my mentor Pete McIntyre for his patience in
working out the details of this project and willingness to answer
my questions. I also would like to thank CLIMFISH (funded
by the Development Cooperation and Science Policy Office,
Belgium) for funding my work as well as Andy Cohen and the
other Nyanza staff that organized the program. I extend special
thanks to Mr Willy Mbemba for his support and computer help
in data analysis. I also would like to acknowledge Mr. George
Kazumbe for his great help in identifying and counting fishes.
Thanks to my felow Nyanza students Happy, Sherry, Tana, Jess,
Matt, and Brittany for their helpful words and smiles.
Arrow indicates the mean.
surveys, so the species they caught differ somewhat from those
we censused. They are probably targeting particular species
that reach higher abundance in the sub-littoral.
Near-shore artesinal fishing appears to play an important part in
the local economy by providing a good income to several dozen
fishermen. Given that 41 fishermen operate along only 20 km
of shoreline, this suggests that the littoral fishing pressure is
substantial, particularly for cichlids. We can estimate the total
daily catch by calculating the average number of fishermen
working per day, and multiplying by their average catch. We
estimate that an average of 35 fishermen harvest enough fish
per day to completely clear an area of 719 m2. Clearly there is
potential for overfishing, and future research should examine
whether any individual species or favorite fishing locations are
being overharvested.
Though cichlids dominated both the fishermen’s catch and
the fish biomass of the littoral zone, the quadrat data should
be interpreted cautiously. Many non-cichlids are nocturnal
and spend the daylight hours in concealment under rocks
and elsewhere (Kawanabe, 1997). These fishes may not have
been seen during our daytime snorkeling censuses, hence
our estimates of fish biomass are certainly underestimates.
The variation among sites in mean fish density, from 2.7-4.3
individuals/m2 (Fig. 5), is probably a result of differences
in habitat type and complexity. More complex habitats
are expected to hold more fishes than less complex (see B.
Huntington, this volume).
Figure 3: Number of individual fishes caught per day
per fisherman. Arrow indicates the mean.
Figure 4: Composition of the near-shore fish catch.
References
Brichard, P. 1978. Cichlids and all other fishes of Lake
Tanganyika. TFH Press.
Coulter, G.W. (Editor), 1991.Lake Tanganyika and its Life.
Natural history publication, Oxford University
Press, London Pp.354
King, M. (1995) Fisheries Biology, Assessment and
Management.Fishing News Books. Pp 87.
Kimaru, J and Msafiri, M. 2002.Line Fishing in Relation to
Limnological Parameters in Kigoma Bay. The
Nyanza Project 2002 Annual Report
Kawanabe,H. (Editor),1997. Fish Communities in Lake
Tanganyika. Kyoto University Press. Pp 243.
Mabochi, H. Kashushu, O., and R. Lindley. 2000. A record of
the Tanzanian fishing gears used in Kigoma region of
Lake Tanganyika at the turn of the millennium. LTBP
Fishing Practices Special Study No. 3.
Figure 5: Mean density of fishes at each census site.
Figure 6: Relationship between daily fish catch and monthly
income.
Figure 7: Composition of the littoral fish community.