Line Fishing in Relation to Limnological Parameters in Kigoma Bay
Students: James Kimaru
Mathias Msafiri
Mentor: Dr. Catherine O’Reilly
Introduction
Lake Tanganyika hosts one of the largest inland fisheries in Africa, and is a significant source of food and
livelihood for millions of people dwelling inside and outside its basin. The lake and its environs support a
wide array of subsistence and commercial activity as well as a remarkable assemblage of tropical flora and
fauna, including a highly diverse population of endemic fish. Also, Lake Tanganyika has a vitally
important pelagic fishery, composed of Lates stappersii (migebuka) and two sardines Stolothrissa
tanganyicae and Limnothrissa miodon (dagaa). Usually fishing is done during the night, using nets
primarily for dagaa, but line fishing is done during the daytime. A lot of studies have examined night
fishing (Nzinza M, Nyanza 2001 and Siaba, Nyanza 2000). Little is known about line fishing at Kigoma
Bay, Therefore this study was aimed at surveying line fishing in relation to limnological parameters.
Study Area
The study areas were Katonga fish landing station (a small village in Bangwe Division situated 4-5 km to
the south of Kigoma Bay), Kibirizi fish landing station (3-4 km from Kigoma town), and Ujiji fish landing
station. Sampling was done within the Kigoma Basin at the following GPS position on 24th July 2002,
latitude: S 040 55.835’ – E 0290 32.284’
Objectives
To determine the limnological parameters in relation to the composition of fish catch (line fishing).
To investigate the knowledge of line fishing from the fishermen themselves by interviewing them.
Hypothesis
High fish catch depends on optimum limnological parameters of the fishing site.
Materials and Methodology
Fishermen questionnaire
Line fishermen were interviewed by means of questionnaires and the total catch is based on an estimation
of what the fishermen have caught. During the interview, we managed to visit the landing stations at
Kibirizi, Katonga and Ujiji and in the process of interviewing we managed to find out about some of the
problems that interfere with fishing activity, such as wind effect and waves. Other than that we asked them
their preferred fishing depth and the number of hooks one can have. See Appendix 1.
Limnological parameters
The following parameters were measured in the field by the CTD; water temperature, dissolved oxygen,
pH, conductivity and turbidity. Water samples were collected from the surface down to 100m at an interval
of 20m for analysis. In laboratory, water samples were analyzed for soluble reactive phosphorous,
alkalinity, nitrate, silica and chlorophyll a. Chlorophyll a was measured by reading the absorbencies at
665nm and 750nm using Spectronixs 21D spectrophotometer after 90% acetone extraction. Nutrients such
as nitrate, phosphorous, and silica were measured by standard methods using a HACH DR/ 2010
spectrophotometer.
Results from fishermen questionnaires
The majority of the fishermen interviewed were fishing during the dry season, with large percent working
from July to October and fishing less in the months of November to January (the wet season) (Figure 1).
The type of fish caught differed at the three landing stations visited. Ujiji fishermen normally fished more
than two species, because the fishermen are fishing in shallow water, catching Bathybates spp, cichlids and
Lates stappersii. At Katonga they catch Lates microlepis, and at Kibirizi they catch Lates stappersii (Figure
2 and 3). The estimate of catch per day indicates that Katonga fishermen catch more fish than any other
station. The reason is that they use bait to catch Lates micropleps, which are also heavy fish (Figure 4).
The total number of fishermen we talked to was 44. Their age and years experience varied and there was
no correlation between age and experience. Some fishermen were 67 years old and had experience of 2
years and other were 40 years old with experience of 30 years (Figure 5). Their income per month also
varied. Katonga fishermen average 35,000 Tsh per month, Kibirizi fishermen average 20,000 Tsh per
month, and finally Ujiji fishermen average only 5,000 Tsh per month. The reason is for these differences in
income is that Katonga fishermen catch bigger fish (Lates microlepis) which are worth more money (Figure
3).
Limnological parameters
Generally water temperature decreased with depth. The surface water temperature measured was 26.49°C
and the temperature at 100m was 24.28°C and the thermocline was between 40 and 67m (Figure 6). The
study showed that pH decreased with depth. Surface pH was 9.05 and at 100 m was 8.87 (Figure 7) but the
CTD reading was 10.05 at the surface and 9.97 at 100m. We did a correction to the CTD readings by
reducing each value by 1.1 (see McAndrews, this volume).
Chlorophyll a values were too low to be detected by the spectrophotometer, even though the volume
filtered was 2L (Figure 11). Nitrate remained constant up to depth of 20m and then increased slightly as
depth increased (Table 1). Total phosphorous decreased at the surface to 50 m and then increased from 60100 m (Table 1). Alkalinity ranged from 287mg/L at the surface to 280mg/L at 100 m (Table 1).
Dissolved oxygen was found to be 5.9mg/L at the surface and increased to 6.78 at 20 m then dropped to
0.07ml/L at 145 m (Figure 8). Conductivity ranged from 675.3 micromhos at the surface and 668.2
micromhos at 100 m with maximum peak at 676 at 43.85 m (Figure 9). Silica showed an increase with
depth up to 40 m before decreasing (Table 1).
Table 1: Summary of the nutrients
Depth
PO-4
NO-3
Silica
(m)
Mg/L
mg/L
mg/L
PO4-3
NO-3 N
SiO2
0
0.18
0.02
0
20
0.3
0.02
16.5
40
0.25
0.03
32.5
60
0.25
0.09
7.8
80
0.34
0.08
0
100
0.35
0.11
0
Chl a
mg/L
Alkalinity
mg/L
Turbidity
-0.0257845
0.0011815
0.000695
-0.0022935
0.000278
-0.0003475
287
315
287
292
288
280
3.41897
3.41897
3.41897
3.41897
3.41897
3.41897
Discussion
The majority of the fishermen interviewed were mainly fishing during the dry season, especially during
July. This is related to the timing and direction of the winds that cause upwelling to the water column
during this month. In May-August, south-east winds drive warm epilimnion water towards the north of the
lake. This causes a tilting of the thermocline. The volume of warm water accumulated in the north depends
on the strength of the wind; thermocline depth is good indicator of the volume of warm water amassed at
the north of the lake (Plisnier et al 1996).
The abundance of fish depends on the availability of the fish food in the water column, and this is directly
related to the availability of nutrients and optimum conditions for growth of phytoplankton and
zooplankton. According to Coulter (1991), nutrients are chemical elements essential for biological growth,
and in tropical lakes, such as Tanganyika, that are highly transparent, continuously warm, and where solar
radiation has little seasonality, nutrients would be expected to limit algal growth. Our results showed that
surface water nitrogen and soluble reactive phosphorous concentrations were low and that there was a small
increase at 100 m. The lake water generally showed oligotrophic characteristics near the surface and higher
concentrations of nutrients in deep water, which to a large extent depend on the regeneration of nutrients
from the hypolimnetic water (Plisnier.et al, 1999).
The line fishermen were only small-scale fishermen. The fish they harvest is mainly for food and
secondarily for cash income. Farming activities during the rainy season interrupt fishing activities. Most of
the line fishermen depend on the strength and direction of the wind for sailing, and sometimes the wind
might be very strong, leading to a loss of equipment and possibly even life. We found that there was no
significant relationship between fish catch and wind speed (Figure 10). The wind station is located at
TAFIRI. Because the fishermen sometimes sail for 2-3 hours from shore, they might encounter a different
wind direction or speed than that which was recorded at TAFIRI.
Fishing depth also differed from one station to another. For example, line fishermen from Katonga that fish
Lates microlepis preferred depths of 1-2 m, while those at Ujiji and Kibirizi preferred depths of 60-100 m.
Lates stappersii accounted for the largest percentage of the fish catch (Figure 10).
Conclusion
The study showed that majority of line fishermen were subsistence fishermen that fish for food and small
cash depending on the catch. The majority of them fish in July, coinciding with the windy season and
higher nutrient concentrations, but they have no knowledge on the limnological changes of the lake.
Acknowledgement
We would like to thank Mr. Willy Mbemba and Catherine for their help from the draft of this work till its
final work. Especially, thanks to go Willy for his laboratory assistance and computer work. We would like
to thank the Nyanza Project for giving us opportunity to explore our interest and the World Wildlife Fund
(WWF) for financing the African students, the crew of the Echo and lastly Kiram Lezzar for head counting
during the journey from Dar es Salaam to Kigoma by BUS.
References
Coulter, G.W.(Ed.). 1991. Lake Tanganyika and its life. Oxford University Press, London.
Makala, N. 2001. Investigation of limnological parameters in relation to composition of fish catches in Lake Tanganyika in the
Kigoma area. The Nyanza Project 2001 Annual Report.
Plisnier, P-D., D. Chitamweba, L Mwape, K. Tshibangu, V. Langenberg, and E. Coenen. 1999. Limnological annual cycles inferred
from physical-chemical fluctuations at three station of Lake Tanganyika. Hydrobiologia 407:45-58, 1999.
Plisnier, P-D., V. Langenberg, L. Mwape, D. Chitamwembwa, K. Tshibangu, and E. Coenen 1994. Limnological sampling during an
annual cycle at three stations on lake Tanganyika (1993-1994). FAO/FINNIDA Research for the Management of the Fisheries on
Lake Tanganyika. GCP/RAF/271/FIN-TD/46 (En): 136 p.
Ramadhani, S. 2000. Nutrient distribution in relation to hydrodynamic changes and primary production: A short-term study at
Kigoma station. The Nyanza Project 2000 Annual Report.
Appendix 1: A SURVEY OF KNOWLEDGE FROM THE LINE FISHIRMEN IN KIGOMA BAY,
LAKE TANGANYIKA
Date……………… Time……………
(a) Name……………………………. (Optional)
(b) Sex:
( ) Female
( ) Male
(c) Age; Tick one of the brackets ( ) 10-20, ( ) 21-30, ( ) 31-40, ( ) 41-50, ( ) 51-60, ( ) 61-70, ( ) 71-80,
( ) 80 & above
(d) Level of Education: ( ) Primary ( ) Secondary
( ) College ( ) University ( ) Other
(e) Where do you live?
(f) How long have you lived in this area? ............................(Years)
(g) What are your main income earning activities (actual or past)................................
Fishing:
(a) What fishing method(s) do you use? ( ) Traditional ( ) Boat ( ) Other……….........…
(b) How many are you usually on a fishing trip? ...........
(c) How long have you been a line fisherman?
(Years)
(d) Was your father also a fisherman? ( ) Yes ( ) No. Who else has been fishing in your family?..............
(e) What are your Fish Catching / Day? ..................... (Monthly). ..................Kg (estimation)
(f) Average annual income……………….
(g) What type of fish do you normally get………………..
(h) What is the depth of the line bait……..m
(i) What is the depth at which you mostly get fish? (Preferred depth)……………..m
(j) What size of the fish do normally get?
(k) Are you making profit on this business? Yes......... No.....
(l) What is the distribution of fish/money amongst your group?
(m) How do you choose a site for fishing and what parameters are you considering?
Winds:
(a) How many types of Winds do you know in the lake?
Wind Name
meaning of the Name
Wind direction
Wind strength
1……………………… ………………………
………………
1…2…3…4…5
2……………………… ………………………
………………
1…2…3…4…5
3……………………… ………………………
………………
1…2…3…4…5
(b) What kind of wind is favorable for your fishing?
Wind Name
Wind direction
Wind strength
1………………………
………………
1…2…3…4…5
2………………………
………………
1…2…3…4…5
(c) What months of the year do you have good production? Wet ( ) Dry ( )
(d) How do you compare the last five years yield and now days in both yield and size of the fish?
1……………………………………………………..
2……………………………………………………..
(e) What problems do encountered in fishing
1.....................................................................................
2......................................................................................
(f) Where do you sell your product/ fish.....................…
(g) Suggestions?
1………………………………………………………...
2…………………………………………………………
Figure 1: Fishing season
Figure 3: Type of fish / landing
station
Figure 2: Species composition of
the fish catch
Nov
1%
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Jan
1%
Oct
21%
Apr
4%
Sep
12%
2%
12%
May
2%
21%
Jun
10%
Aug
13%
65%
Jul
36%
Lates stapersii
Bathybates spp
Figure 4: Estimated catch /
day in Kg
7
Kg
6
5
4
3
2
1
Kibirizi
Katonga
Ujiji
Landing station
35
Kibirizi
Cichlids
Lates microlepis
temperature oC
24.5
25.5
26.5
23.5
0
R2 = 0.041
30
Katonga
Figure 6: temperature-depth
profile
27.5
20
25
40
20
Depth (m)
Experience of the fishermen (yrs)
8
Ujiji
Bathybates spp
L.stapesii
Figure 5: Age and Experience of
the fishermen
9
0
Lates microlepis
Cichlids
15
10
5
0
60
80
100
120
0
20
40
60
80
140
Age of the fishermen (yrs)
160
Figure 7: pH-Depth profile
pH
8.7
8.8
8.9
conductivity (micromohs)
9
9.1
9.2
0
20
0
40
20
2
4
6
8
100
120
60
80
100
60
80
100
120
120
140
140
140
160
160
160
Figure 10: Fish catch in relation to wind
speed
3.5
40
1
0.8
0.6
20
0.4
10
Figure 11: Turbidity and Chlorophyll a
4 Turbidity (NTU)4.5
5
0
40
Depth (m)
1.2
wind speed(m/s)
50
30
675
40
Depth (m)
80
670
20
40
60
Depth (m)
Depth (m)
665
0
Disolved oxygen ( mg/L )
0
Catch (Kg)
Figure 9: conductivity
Figure 8: Disolved oxygen depth
profile
80
0.2
0
17
-
Ju
l- 0
2
19
-J
ul
-0
2
21
-J
ul
-0
2
23
-J
ul
-0
2
25
-J
ul
-0
2
27
-J
ul
-0
2
29
-J
ul
-0
2
31
-J
ul
-0
2
0
Man1
Man2
W.S.
120
0
0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014
Chlorophyll a (ug/L
Turbidity
Chrolophyll a
680