Braimah L.I., 1995.- Recent developments in the fisheries of Volta lake (Ghana) In
Crul, R.C.M. & Roest, F.C., (eds), Current status of fisheries and fish stocks of the four
largest African reservoirs: Kainji, Kariba, Nasser/Nubia and Volta. FAO, CIFA
Technical Papers 30, 142 p.
RECENT DEVELOPMENTS IN THE FISHERIES OF VOLTA LAKE
(GHANA)
by
L.I. Braimah
ABSTRACT
No significant limnological change has been reported in
Lake Volta since earlier studies.
The influx of fishermen and associated increased
population pressure have led to an overexploitation of the
resources. Fish stocks are subject to excessive fishing
pressure, while, concomitantly, the main food source of
the fish stocks - periphyton attached to submerged trees is threatened as the trees are increasingly cut during
drawdown periods because of the increased demand for
firewood.
Although the estimated total yield of 36 360 t in 1991
does not appear to be far removed from the long-term yield
of 40 000 t/year predicted by Vanderpuye, fishing effort
(i.e., the number of fishermen) is believed to have
increased at least four-fold over the period 1971–1990.
Low yields of gill net catches have led to the
introduction of a whole range of new fishing techniques,
including semi-mechanized purse seining and beach seining,
which have aggravated the overfishing situation. Although
many of these new methods are prohibited, there is no
effective control.
Traditional experimental gill net catches no longer
reflect commercial catch magnitude and composition.
Fisheries development activities resumed in the reporting
period through the UNDP/FAO IDAF Project, and included an
element of research in the Yeji area of the lake. For lack
of data, some of the findings in this area were
extrapolated to estimate the lakewide situation.
1. INTRODUCTION
This document is an update of a report on Fisheries and
Limnology of Volta Lake, prepared by Vanderpuye (1984).
The limitation of the update is attributable to the fact
that since the termination of the FAO Volta Lake Research
and Development Programme (VLRDP) in 1978, no organization
or institution endeavoured to continue work on limnology
and biology until 1989, when the University of Ghana and
the Institute of Aquatic Biology (IAB) undertook an
investigation into the limno-chemistry and biology of the
lake.
This document analyses data on commercial fish landings
kept over the years by personnel of the Department of
Fisheries stationed in almost all the major marketing
centres along the lake, as well as estimations of total
commercial landings, species compositions, etc., for all
the eight strata of the lake.
The fishery itself is dominated by newly introduced and
alien fishing methods, most of which are nominally
illegal, but which provide as much as 65–70% of the total
fish landings in the marketing centres. The newly
introduced gears tend to be species specific, unlike the
gears deployed on the lake in the 1970s and early 1980s.
Studies on the effect of such species-specific
exploitation were begun at the same time as other studies
on various biological parameters. These were an activity
of the Integrated Development of Artisanal Fisheries
(IDAF) project, based at Yeji since its inception in 1989.
Outputs of this project have been extensively used, and
form the major source for this update.
2. LIMNOLOGY
2.1 WATER LEVEL
After the closure of the dam in 1964, the lake reached its
maximum level of 84 m in 1968. Seasonal variations were
relatively moderate until 1975, when the water level
started to drop. In June 1984, the lake reached an
unprecedentedly low level of 71.9 m. At this level the
lake had shrank to roughly half of its maximum size. Since
then, the lake level has fluctuated, but has been
generally rising. The lake reached its maximum level again
in 1989, and again in 1991 (Figure 1).
Figure 1
Figure 1 Lake levels at Akosombo in the period 1971 to
1991
2.2 WATER CHEMISTRY
Physio-chemical data collected by Antwi (1990) at Ajena in
1989, 25 years after dam closure, are summarized in Table
1. His observations are in line with those of Biswas
(1966) and Obeng-Asamoah (1984).
The lake is warm polymictic. Stratification is fairly
stable in the period April–June, but frequently broken
down in the rest of the year by southerly and harmattan
winds, and the annual floods.
Conductivity values ranged between 67.87 and 75.10
μmhos/cm at 25°C and total dissolved solids (TDS) between
30.60 mg/l and 37.92 mg/l in 1989. Obeng-Asamoah (1984)
noted that the Ph of the surface water was about 7,
declining with depth to 6.45 in the anoxic water near the
bottom of the lake. Total alkalinity increased during the
filling and post-impoundment phases (Biswas, 1966) and a
total alkalinity of 41 mg CaCO3/l was observed in 1989.
The nutrient content of the lake has generally remained
low, and only traces of phosphate, nitrate, nitrite,
ammonia and sulphate have been recorded in the upper 40 m
of the lake, while measurable quantities of these ions
were recorded in the bottom waters. The low nutrient
content was attributed to the catchment area itself being
poor in nutrients, and also due to the low solubility of
the pre-Cambrian rock granites found in the upper
catchment area (Antwi, 1990).
Mean Secchi disc transparency was 2.2
1990). The depth of light penetration
reduced during the flood period (July
during the harmattan seasons, as also
(1966).
m in 1989 (Antwi,
was drastically
to September) and
observed by Biswas
Gross primary productivity measurements at the surface
estimated by Antwi (1990) are shown in Table 2. In general
the primary productivity values were low, ranging from 0.2
g C/m3/day to 1.35 g C/m3/day due to the limited supply of
nutrients.
Table 1 Physico-chemical data at Ajena, Volta Lake
Parameter DEPTH
0 m 1 m 5 m 10 m 15 m 20 m 30 m 40 m 50 m 60 m 70 m
Temperature (°C) 29.1 28.7 28.6 28.1 27.8 27.5 26.8 26.7
26.5 26.1 26.1
pH 7.0 7.1 7.1 6.9 6.9 6.9 6.7 6.7 6.7 6.6 6.6
Oxygen (mg/l) 11.8 8.5 8.8 7.5 5.9 5.0 4.6 3.0 2.2 1.8 0.4
Oxygen (% sat.) 138.1 110.8 87.1 86.7 67.0 60.0 49.4 35.7
24.5 17.7 5.9
Acidity (mg/l CaCO3 16.8 16.9 17.8 17.7 17.7 18.5 18.2
19.1 19.6 20.8 24.1
Alkalinity (mg/l CaCO3 40.8 40.7 40.6 41.5 42.4 40.4 41.1
42.8 41.8 40.3 39.9
Total hardness (mg/l CaCO3 27.1 27.3 27.9 26.9 28.0 25.8
29.1 31.3 28.9 26.9 26.1
TDS (mg/l) 34.9 35.1 37.0 37.9 34.5 33.9 34.2 34.7 35.4
35.2 30.8
Conductivity (μmhos/cm at 25°C) 68.8 67.9 74.8 64.8 67.3
68.7 69.6 68.6 71.2 72.6 75.1
Sodium (mg/l) 3.9 4.0 4.2 4.0 3.8 4.0 3.9 3.8 3.8 3.1 3.8
Potassium (mg/l) 2.1 2.3 2.4 2.0 2.6 2.3 1.9 2.0 2.0 2.2
3.0
Calcium (mg/l) 5.7 5.8 5.8 5.4 5.4 5.5 5.1 6.0 5.8 6.0 6.1
Magnesium (mg/l) 4.2 4.0 4.2 4.1 4.6 3.8 4.7 5.2 4.4 3.9
3.5
Chloride (mg/l) 7.7 7.5 7.7 7.5 7.6 7.5 7.6 7.6 7.6 7.3
7.3
Orthophosphate (μg/l) 3 4 2 3 7 4 6 8 18 27 240
Nitrate (μg/l) 50 40 70 40 40 50 80 110 130 180 190
Nitrite (μg/l) 5 13 6 6 6 40 20 20 90 90 50
Ammonium (μg/l) 10 20 10 10 2 6 40 50 100 110 270
Silicate (mg/l) 3.1 3.1 3.1 3.0 3.0 3.3 3.7 3.4 2.8 3.5
5.4
Sulphate (mg/l) 0.2 0.6 0.4 0.3 0.3 0.4 0.3 0.7 0.7 0.8
6.2
Secchi disc (m) 2.2
Notes: Values are mean (x) over sampling period: February
to December, 1989. Sampling frequency: once a month.
(Source: Antwi, 1990)
Table 2 Gross primary productivity measurements at Ajena
in 1989
Depth Month Gross primary productivity
(g C/m3/day)
1 metre April 0.20
1 metre May 0.48
1 metre August 1.27
Surface (0 m) September 0.20
1 metre September 0.20
Surface (0 m) October 0.20
1 metre October 0.20
Surface (0 m) November 1.35
1 metre November 1.32
(Source: Antwi, 1990)
2.3 PHYTOPLANKTON AND ZOOPLANKTON
Plankton in the southern part of the lake was
quantitatively poor and the number of species low
(Rajagopal, 1969), and algal blooms were only observed
occasionally in some areas (Obeng-Asamoah, 1984). The
number of species was just over twenty and confined to not
more than 10 genera. The most abundant species were
Synedra and Melosira for the main channel, while
Oscillatoria dominated the shallow arms and inshore areas.
Eudorina and Volvox also occurred in relatively large
numbers (Obeng-Asamoah, 1984).
As observed by Biswas (1966), the rotifers formed the
major constituent (about 90%) of the zooplankton; and
copepods, cladocerans and protozoa were present in much
smaller numbers (Obeng-Asamoah, 1984).
2.4 PERIPHYTON, AUFWUCHS AND BENTHOS
The flooded trees in Volta Lake provide a substrate for
periphyton in the epilimnion of the inshore and offshore
areas (Vanderpuye, 1984). The bulk of invertebrate
organisms living on the mats of periphyton are members of
the following taxa: Ephemeroptera (Povilla adusta and,
less commonly, the mayflies), Diptera (chironomids),
Trichoptera and Coleoptera.
Examination of the commercial catches in 1991 shows that
52% of the fish caught depend on these aquatic organisms.
Vanderpuye's solution of having cleared and uncleared
parts in the lake is valid as long as a suitable balance
is struck in order not to inhibit the survival of these
aquatic organisms.
Over the years, fishermen have found the petrified
submerged trees very useful and effective fuel for fish
processing (smoking), and have started to exploit them at
an alarming rate, cutting them during drawdown periods.
The drought of 1984 reduced the lake to half of its
maximum size and at this half capacity a significant
percentage of the submerged trees were exposed to
exploitation as firewood. Large expanses of submerged
trees are also being cleared to make room for increased
beach seine operations. These practices, although
escalating, are not yet sufficiently significant to offset
the predominance of the periphytonic biomass over the
benthic.
2.5 LAKE PRODUCTIVITY
According to Baranov (1961), Ioeffe (1961) and Tyurin
(1961), large reservoirs can be placed in one of five
categories, using fish production or benthic production
levels as criteria (Table 3).
Table 3 Classification of reservoirs by fish production
and by benthic production
Trophic state of reservoir Fish production
(kg/ha/year) Benthic biomass production
(kg/ha)
Oligotrophic 2–7 <15
Oligotrophic-mesohumic 7–15 15–30
Mesohumic-mesotrophic 15–30 30–60
Mesotrophic-eutrophic 30–60 60–120
Eutrophic >60 >120
On the basis of Table 3, Volta Lake, having a yield of 42–
52 kg/ha/yr, is mesotrophic-eutrophic, rather than the
oligotrophic that might be assumed based on the nutrient
content (Antwi, 1990). The possible reconciliation of this
paradox was outlined by Obeng-Asamoah (1977). The
essential nutrients released by the breakdown and
mineralization of the organic load are immediately picked
up by the algae and Ceratophyllum. This process is fuelled
by the high water temperature, resulting in quick turnover
and high net productivity. Consequently, the measurement
of the TDS alone gives an erroneous picture of the
nutrient status of the lake: hence the conclusion of
oligotrophy.
The potential fish yield calculated with the Morphoedaphic Index Model was approximately 12 kg/ha, while the
fish yield based on catch statistics for the lake in 1991
was 43.4 kg/ha (Table 4).
Table 4 Catch statistics for Volta Lake in 1991
A. Total processed fish landings (FWE in kg)
Fish Market Stratum Total processed fish
(FWE - kg) Total processed per stratum
(kg)
Yapei* VIII 882 450
Bupei VIII 3 688 137 4 570 587
Yeji VII 9 891 411
Makango VII 307 196 10 198 608
Kete-Krachi* VI 1 815 303 1 815 303
Dambai V 1 443 130 1 443 130
Kwame-krom IV 1 198 732
Tapa-Abotoase IV 1 641 181 2 839 913
Kpando-Torkor III 2 399 783 2 399 783
Dzemeni II 1 047 617 1 047 617
Nketepa* I 5 309 328 5 309 328
TOTAL
29 624 270
Note: * = Estimated (with 95% confidence limit) using
trends in fish landings per transport boat at Yeji.
B. Estimated yield based on catch statistics in 1991
Total processed fish landings in 1991 29 624 t
Total landings of fresh fish in 1991 1 464 t
Total fish landings 31 088 t
Plus adjustment for self-consumption by fisherfolk
(11.7% of total landings)
3 636 t
Plus adjustment for post-harvest losses
(5.3% of total landings)
1 636 t
Total fish production from Volta Lake 36 360 t
Surface area of Lake at 275 ft water level 837 617 ha
Therefore estimated yield in 1991 43.4 kg/ha
3. FISHERIES
3.1 FISHING EFFORT
3.1.1 Fishing sites, canoes and fishermen
Volta Lake has been divided into 8 strata for recording
purposes (Figure 2).
Figure 2
Figure 2 Map of Volta Lake, showing the eight strata
Two major frame surveys - in 1970 and 1975 - provided
details on the fishing effort on Volta Lake (Table 5)
(Bazigos, 1970; Coppola and Agadzi, 1976). Since the last
survey, in 1975, no surveys have been carried out.
However, socio-economic studies conducted in 1989 by
Agyenim-Boateng (1989) and in 1991 by Maembe (1991)
provided updates on some of the elements for Stratum VII
(the Yeji part) of the lake (Table 6).
As there are currently no plans to execute a frame survey
to cover the entire lake, a crude estimate has been made
for the whole lake using the data collected for Stratum
VII. The estimated fishing effort (fishing sites,
fishermen and canoes) for 1991 is given in Table 5. On the
basis of that estimate, the number of fishermen on the
lake obtained would have been 82 460, while the official
figure often quoted by the Fisheries Authorities was 80
000. This represents a four-fold increase over the period
1971–1990.
Table 5 Fishing effort for the whole lake, based on 1970
and 1975 frame surveys, and estimation of fishing effort
for the whole lake in 1991, based on developments in
Stratum VII
Year No. of fishing sites No. of fishers No. of canoes No.
of gear per day
Gill net Cast net Line Other
1970(1) 1 259 18 358 12 074 56 921 323 9 504 15 993
1975(2) 1 479 20 615 13 814 61 107 367 10 472 434
1991(3) 2 500 82 460 46 277 - - - Sources: (1) Bazigos, 1970;
(2) Coppola and Agadzi, 1976;
(3) Estimate based on stratum VII (see Table 6).
Table 6 Fishing effort for Stratum VII (1975, 1989 and
1991)
Period No. of fishing sites No. of fishers No. of canoes
No. of canoes with engine
1975(1) 202 100% 4 562 100% 1 913 100% 0
1989(2) 190
15 581
4 266
259
1991(3) 342 169% 18 302 401% 6 407 335% 421
Sources: (1) From Coppola and Agadzi, 1976;
(2) From Agyenim-Boateng, 1989. Note that minor villages
were grouped under group names;
(3) From Maembe, 1991.
3.1.2 Fishing Gears
All the fishing inputs have increased by leaps and bounds
over the years and the effectiveness of fishing increased
due to new and more effective fishing gears and more and
larger outboard engines. The combination of these factors
has resulted in increased fishing efficiency and increased
fishing pressure on the stocks.
In 1970 and 1975, the principal fishing gears used on the
lake were gill nets, cast nets, lines and traps (Bazigos,
1970; Coppola and Agadzi, 1975). The gill nets used in the
1960s and 1970s ranged from 102 to 205 mm (Vanderpuye,
1984), but the smallest have now been reduced to below 25
mm.
Recently, other gears have been introduced (Braimah, 1989,
1991) including drivein gear (wangara), bamboo-pipe
fishing (specifically for Chrysichthys), combined gill
nets and traps (nifa nifa) and some active gears, such as
beach seines (adranyi), purse seines (winched) and other
forms of encircling gear. These active gears are
supposedly illegal on the lake, but currently contribute
between 65 and 70% of the total fish landings of the lake
(unpublished IDAF report, 1990).
The introduction of purses seines (winch nets) on the lake
since the mid-1980s was concomitant with the deployment of
a new type of craft for fishing, called a winch boat. This
craft has a length overall of 9 to 13 m and a breadth of
over 1 m. The incorporation of an operational deck allows
10 to 15 fishermen to stand easily while working with the
net, which can be as long as 500 to 800 m and 20 to 30 m
deep. The normal canoes are still the most prevalent, but
their capacity has commonly increased from 6 to 7 boards
to 10 to 12, and lengths range between 5 and 10 m, with 2
to 4 fishermen.
Most of the fishermen are forced to fish in inshore waters
due to the activity of winch net operators (purse
seiners), who foul nets of other fishermen during
operations in the offshore area because due to the
presence of tree stumps, purse seines are used only in the
original river bed.
Until 1975, there were no transport boats on the lake
(Coppola and Agadzi, 1976), while currently there are
nearly 1 000 boats, with the Yeji market alone visited by
over 100 (Agyenim-Boateng, 1989; Maembe, 1990). These
boats - with an overall length of 13 to 20 m and a breadth
between 2.2 and 2.5 m (van der Straten, 1990, 1991) - have
now become, throughout the lake, the major means of
transportation, instead of canoes.
The 1975 frame survey of the lake did not mention the
presence of any outboard motors for propulsion. AgyenimBoateng (1989) recorded 259 outboard motors, while in
1991, Maembe found 421, an increase of about 63% in two
years. These outboard motors ranged between 9.9 and 45 HP.
A few gill net and long-line fishermen use outboards,
mostly of 9.9 and 15 HP, while the purse seine operators
use mainly 25 HP motors. The lake transporters operate the
45 HP engines, of which they often have 2 or 3 mounted on
the transom of the boat.
3.2 FISH PRODUCTION
3.2.1 Commercial Catches
Fish production figures for Volta Lake from its creation
in 1964 to 1979 are given by Vanderpuye (1984). Fish
production in 1991, estimated from commercial landings at
the marketing centres along the lake, was 36 360 t (Table
4). The fish yield pattern showed an initial steady rise
to a maximum of almost 62 000 t in 1969 - the highest
yield ever recorded for a man-made lake - followed by a
decline and stabilization at around 40 000 t. The 1991
figure is not at variance with the statistical prediction
of Vanderpuye that annual fish production would fluctuate
around 40 000 t/yr. Fishing effort, however, has probably
increased more than fourfold (Table 5).
Length frequency data on 26 commercial important fish
species collected by the IDAF project indicates that 17
fish species are caught before reaching the age of one
year (Goudswaard and Avoke, 1993). The high mortality of
the juvenile length classes of these fishes is caused by
the extensive use of small-meshed gill nets and recently
introduced active gears, such the purse and beach seines
that provide between 65 and 70% of the total commercial
landings (unpublished IDAF report, 1990). Lake level
fluctuations and monthly commercial fish catches were
recorded in the Yeji part of the lake from July 1989 to
December 1991 (Figure 3). Fish catches were high when lake
levels were low and vice versa. The general trend of
monthly fish catches for the Yeji part of the lake is very
much influenced by the high Tilapia catches (Figure 4).
When lake levels are high, Tilapia catches are low, and
vice versa.
Figure 3
Figure 3 Lake levels and commercial catches in Stratum VII
(July 1989 – December 1991)
Figure 4
Figure 4 Landings of four species in Stratum VII (July
1989 – December 1991)
Table 7 Processed fish landings (fresh weight equivalent
(FWE) in kg), Volta Lake, 1991, based on recorded figures
SPECIES MARKET
Buipe Yeji Makango Dambai Tapa-Abot. Kwame-krome Kpando
Dzemeni Total
FWE in kg % FWE in kg % FWE in kg % FWE in kg % FWE in kg
% FWE in kg % FWE in kg % FWE in kg % %
Lates 4 916 0.1 128 422 1.3 290 0.1 53 842 3.7 168 500
10.3 64 545 5.4 140 902 5.9 121 949 11.6 3.2
Hemichromis 0 0 0 - 0 - 0 - 0 - 254 <0.1 4 558 0.2 0 - 0
Tilapia 823 601 22.3 2 898 567 29.3 54 891 17.9 318 406
22.1 142 586 8.7 295 533 24.7 839 632 35.0 216 767 20.7
25.9
Heterotis 101 109 2.7 228 774 2.3 2 140 0.7 44 085 3.1 102
623 6.3 49 800 4.2 41 478 1.7 38 983 3.7 2.8
Clupeidae 0 - 91 892 0.9 10 228 3.3 1 921 0.1 278 <0.1 5
984 0.5 0 - 91 <0.1 0.5
Labeo 294 957 8.0 338 973 3.4 10 298 3.4 38 447 2.7 9 593
0.6 1 976 0.2 788 <0.1 370 <0.1 3.2
Mormyridae 101 852 2.8 286 471 2.9 7 142 2.3 39 965 2.8 43
954 2.7 21 506 1.8 85 093 2.7 25 108 2.4 2.7
Hydrocynus 16 076 0.4 41 606 0.4 690 0.2 53 462 3.7 251
948 15.4 165 697 13.8 321 962 13.4 130 608 12.5 4.5
Alestes 93 419 2.5 63 545 0.6 1 680 0.5 18 962 1.3 0 - 857
0.1 4 466 0.2 4 489 0.4 0.9
Citharinus 347 282 9.4 257 696 2.6 10 172 3.3 216 903 15.0
126 376 7.7 45 735 3.8 3 033 0.1 1 360 0.1 4.7
Distichodus 29 492 0.8 16 982 0.2 0 - 11 180 0.8 51 644
3.1 4 282 0.4 1 340 0.1 1 487 0.1 0.5
Schilbeidae 100 501 2.7 205 187 2.1 8 484 2.8 12 813 0.9 3
068 0.2 26 423 2.2 7 842 0.3 0 - 1.7
Bagrus 71 983 2.0 215 756 2.2 8 200 2.7 56 838 3.9 142 580
8.7 78 158 6.5 703 782 29.3 102 941 9.8 6.4
Synodontis 988 495 26.8 1 434 162 14.5 45 362 14.8 221 007
15.3 281 617 17.2 127 624 10.6 232 786 9.7 88 786 8.5 15.4
Chrysichthys 480 324 13.0 3 451 443 34.9 121 226 39.5 236
364 16.4 273 074 16.6 275 259 23.0 0 - 162 582 15.5 23.1
Auchenoglanis 25 231 0.7 0 - 0 - 51 239 3.6 4 053 0.2 10
060 0.8 0 - 37 643 3.6 0.6
Gymnarchus 24 011 0.7 67 951 0.7 0 - 6 418 0.4 413 <0.1 2
106 0.2 0 - 24 365 2.3 0.6
Clarias 184 889 5.0 163 984 1.7 26 394 8.6 45 270 3.1 36
437 2.2 19 233 1.6 0 - 48 841 4.7 2.4
Others 0 - 0 - 0 - 16 007 1.1 2 439 0.1 3 600 0.3 32 125
1.3 41 247 3.9 0.4
TOTAL 3 688 137 100 9 891 412 100 307 196 100 1 443 130
100 1 641 182
1 198 732
2 399 783
1 047 617 100 100
VIII VII V IV III II
STRATUM
During floods, turbid flood water (usually referred to as
white water) can be traced well past Kete-Krachi in
Stratum VI. The whole northern arm then becomes riverine,
which induces fish to spawn. Tilapias avoid such turbid
currents and hence are very rare in the catches during
floods.
In the period April – June 1991, fish catches were not
high, although lake levels were low. This was caused by
the fact that the new Fisheries Law of 1991 was launched
at Yeji in April 1991. It explicitly banned the use of all
active gear on the lake. To begin with, the law was
observed, but when it became clear that a mechanism for
enforcement was lacking, fishing with these banned gears
started again full force.
Previous Page Top of Page
RECENT DEVELOPMENTS IN THE FISHERIES OF VOLTA LAKE
(GHANA) (continue)
3. FISHERIES (continue)
3.2 FISH PRODUCTION (continue)
3.2.2 Species composition of commercial catches
Table 7 shows the percentage composition by weight of the
processed fish species in the commercial fishery in 1991.
Tilapia is the dominant species (25.9%) closely followed
by Chrysichthys spp. (23.1%) and Synodontis spp. (15.8%).
Clupeids - which did not exist at all in the commercial
fishery in the earlier days - now generally constitute
0.5% of the total catch. The dominance of Tilapia in the
commercial catches is the result of the use of the wangara
net (gill net combined with traps) which is specific for
Tilapia. Species composition of the commercial catches
differed per stratum in 1991. For six strata, the four
most important species are given in Table 8. Tilapia
appears in all strata, while Chrysichthys appears in 5 and
Hydrocynus in 4 strata.
The main species in the fresh fish landings in 1991 were
Chrysichthys (32.9%), Synodontis (23.5%) and Tilapia
(12.4%). A survey by Loiselle (1972) of the inshore
habitats gave a similar species composition, indicating
that most fishermen are fishing in inshore waters.
3.2.3 Species composition of experimental catches
In experimental gill nets catches in the Akosombo gorge
(Stratum II) in 1989, 39 fish species from 28 genera and
13 families were found (Table 9). The catches were
dominated by Characidae (52.4%), followed by Mochokidae
(10.7%), Mormyridae (8.2%), Bagridae (8%) and Cichlidae.
Almost 90% of the gill net catches in the Akosombo gorge
came from gill nets with mesh sizes between 15 mm and 63.5
mm (Table 10), while the 63.5 mm gill nets produced the
highest catches (Ofori-Danson 1990). This indicates that
all main commercial fish species in Volta Lake are
overexploited.
Yamamoto (1991) listed the species composition of catches
from experimental gill nets with various mesh sizes in the
Yeji area (Stratum VII). Catches of 4-inch nets were
dominated by Bagridae (Chrysichthys spp.) (27.8%) and
Mochokidae (Synodontis spp.) (20.7%), followed by
Mormyridae (18.1%). Gill nets of 1 inch (25 mm) mesh size
and below caught predominantly clupeids (63.6 – 71.8%) and
nets with bigger mesh sizes caught fish species belonging
to the families Bagridae, Mochokidae, Mormyridae and
Cyprinidae.
Braimah (1991) conducted efficiency tests on newly
designed gill nets (88 mm mesh size) at ten fishing sites
in Stratum VII (the Yeji part of the lake). Main species
in the catches were Synodontis spp. (54.2%), Chrysichthys
spp. (18.1%) and Mormyridae (7.6%).
3.2.4 Comparison of commercial and experimental catches
Comparison of the species composition of the commercial
and experimental catches revealed large differences.
Vanderpuye (1984) found a high correlation between
experimental and commercial catches, and experimental
catch data proved to be a good indicator of trends in
commercial catches. However, due to the selectivity and
species specificity of newly introduced gears,
experimental catch data can no longer be used to predict
commercial catches.
Table 8 Four most important species in commercial catches
in six strata
STRATUM AND STATION
II: Dzemeni III: Kpando IV: Kwame-krome V: Dambai VII:
Yeji VIII: Bupei
1 Tilapia Tilapia Tilapia Tilapia Chrysichthys Synodontis
2 Chrysichthys Bagrus Chrysichthys Chrysichthys Tilapia
Tilapia
3 Hydrocynus Hydrocynus Hydrocynus Synodontis Synodontis
Chrysichthys
4 Lates Synodontis Bagrus Citharinus Labeo Labeo
Table 9 Checklist of species in the Akosombo Gorge area of
Volta Lake in 1989–90, based on gill net catches
FAMILY SPECIES
1) Clupeidae 1) Pellonula afzeliusi
2) Cynothrissa mento
3) Sierrathrissa leonensis
2) Osteoglossidae 4) Heterotis niloticus
3) Mormyridae 5) Mormyrus deliciosus
6) Mormyrus rume
7) Hippopotamyrus pictus
8) Pollimyrus isidori
4) Characidae 9) Brycinus nurse (= Alestes nurse)
10) Brycinus leuciscus (= A. leuciscus)
11) Brycinus macrolepidotus (= A. macrolepidotus)
12) Hydrocynus forskahlii
13) Hydrocynus lineatus
5) Cyprinidae 14) Labeo coubie
15) Raiamas senegalensis
6) Bagridea 16) Bagrus docmac
17) Bagrus bayad
18) Chrysichthys nigrodigitatus
19) Chrysichthys walkeri
20) Chrysichthys auratus
21) Auchenoglanis occidentalis
7) Mochokidae 22) Synodontis gambiensis
23) Synodontis ocellifer
24) Synodontis schall
25) Synodontis eupterus
26) Synodontis velifer
8) Schilbeidae 27) Schilbe myatus
28) Siluranodon auritus
9) Malapturidae 29) Malapterurus electricus
10) Centropomidae 30) Lates niloticus
11) Cichlidae 31) Sarotherodon galilaeus (= Tilapia
galilaea)
32) Oreochromis niloticus (= Tilapia nilotica)
33) Tilapia zilii
34) Chromidotilapia guentheri
35) Leptotilapia irvinei
36) Hemichromis bimaculatus
12) Anabantidae 37) Ctenopoma kingsleyae
13) Tetradontidae 38) Tetraodon fahaka
Table 10 Experimental fishing distribution of CPUE by mesh
size of gill nets used in Akosombo Gorge during the dry
and wet season in 1989
Stretched mesh size of net (mm) Catch per unit effort
(CPUE)
in wet season (October) in dry season (December)
Number Weight Number Weight
15.0 10.5 249.1 5.5 276.8
20.0 5.0 387.0 11.5 621.6
25.0 4.5 301.0 1.5 143.0
30.0 7.0 69.0 1.0 65.8
40.0 0.0 0.0 1.0 164.3
63.5 2.5 1 781.0 1.5 432.1
101.6 0.0 0.0 0.5 182.1
114.3 0.0 0.0 0.0 0.0
127.0 0.5 375.0 0.0 0.0
139.7 0.0 0.0 0.0 0.0
152.4 0.0 0.0 0.0 0.0
177.8 0.0 0.0 0.0 0.0
(Source: Ofori-Danson, 1990)
While in the 1970s and early 1980s the common fishing
gears were gill nets (producing 80% of the catch), cast
nets, lines and traps, other, more efficient gears, have
been recently introduced, including purse seines (winch),
beach seines (adranyi), bamboopipe fishing and drive-in
gear (wangara). Small-meshed purse seines and beach seines
contribute between 65–70% of the total commercial landings
(unpublished IDAF report, 1990). Bamboo-pipe fishing introduced in 1991 - is specific for Chrysichthys spp. and
is responsible for the sudden rise in percentage
contribution by body weight of Chrysichthys spp. to the
commercial landings (23.1%), while the gill net combined
with traps (nifa nifa) is specific for Tilapia.
Analysis of the experimental and commercial catches
clearly reveals that most commercial fish species in Volta
Lake are overexploited.
Vanderpuye (1976) concluded from his work on species
distribution that some species were mainly limited to
estuarine or to riverine environments, e.g., Hydrocynus
spp., Labeo spp., mormyrids, schilbeids, Cynothrissa
mento, Brycinus nurse, Alestes baremose, Alestes dentex
and Citharinus spp.
However, data on the commercial fish landings along the
lake show that some of these species have penetrated into
what were originally described as lacustrine strata (I, II
and III). Table 11 shows that some of the species are
almost uniformly distributed throughout the lake. This may
indicate that conditions in the lake have become uniform
and that the lake has more or less stabilized.
Table 11 Percentage composition per stratum of riverine
species in commercial catches (processed fish) in 1991
Station Buipe Yeji Makango Dambai Tapa-Abotose Kwame-krom
Kpandu Dzemeni
Stratum VIII VII VII V IV IV III II
Hydrocynus 0.4 0.4 0.2 3.7 15.4 13.8 13.4 12.5
Mormyridae 2.8 2.9 2.3 2.8 2.7 1.8 2.7 2.4
Alestes 2.5 0.6 0.5 1.3 0.0 0.1 0.2 0.4
Synodontis 26.8 14.5 14.8 15.3 17.2 10.6 9.7 8.5
3.2.5 Diversity and ecogroups
Commercial catches comprise only 18 genera. The recording
does not include a breakdown of the different species. In
the absence of experimental catch data for the lake,
commercial fish landings might give an insight into the
size of the components of the eco-groups described by
Vanderpuye (1984). Using his categorization, the insectaufwuchs and detritus herbivore feeders predominate
(52.9%), with Tilapia alone contributing 25.9%, while the
piscivores were the second ecogroup (37.8%), followed by
the benthic-omnivores (5.7%) and the semi-pelagic
omnivores (3.6%) (Table 12).
Table 12 Main feeding group categories as percentage
composition based on fresh weight equivalent (FWE) fish
landings, 1991
Insect-aufwuchs, detritus feeders and herbivores
Piscivores Semi-pelagic omnivores Benthic-omnivores
Species % Species % Species % Species %
Heterotis niloticus 2.8 Polypterus senegalus
Clupeidae
0.5 Mormyridae 2.7
Distichodus 0.5 Gymnarchus niloticus
Schilbeidae
Auchanoglanis 0.6
Citharinus 4.7 Hydrocynus spp. 4.5 Alestes 0.9 Clarias 2.4
Labeo 3.2 Chrysichthys spp. 23.1 Distichodus 0.5
Synodontis 15.8 Bagrus spp. 6.4
Tilapia spp. 25.9 Lates niloticus 3.2
Tetradon fahaka
Total % FWE 52.9
37.8
3.6
5.7
3.2.6 Standing crop of fish
The survey by Loiselle (1972) showed that the highest
ichthyomass was in the interphase between the lacustrine
and riverine parts of the lake (Stratum IV), followed by
the southern lacustrine (Strata I, II and III). The
poorest area was the northern riverine part (Strata V to
VIII). To a certain degree, catch per unit effort (CPUE)
data for these areas should reflect the ichthyomass
distribution, but this could not be observed in the
compiled CPUE data for 1991 (Table 13) (Braimah, 1992).
The CPUE figures are uniform, which might indicate that
the ichthyomass distribution is also uniform. This may be
further evidence that the lake has stabilized, although
fluctuation in lake level will always be a major
destabilization factor affecting fish species composition
and fish landings.
Table 13 Average CPUE per day stratum (kg/canoe/day) on a
monthly and annual basis
Stratum and Station
VIII Buipe VII Yapei VII Yeji V Dambai IV Tapa-Abotase III
Kpando-Tor II Dzemeni Whole Lake
Jan.
18.10
10.70 9.27 19.59
Feb.
17.40
6.19 7.14 9.69
Mar.
10.20
6.28 7.29 8.00
Apr.
13.60 12.86 8.80 8.58 11.11
May.
9.30 6.41 7.93 8.63 11.38
Jun.
10.50 6.98 8.07 8.67 19.92
Jul.
8.40 7.01 12.07 9.91 8.80
Aug.
7.20 3.89 12.05 12.66 3.81
Sep.
7.40 3.59 8.21 10.95 3.40
Oct.
3.10 15.00 4.75 9.62 2.93
Nov.
5.00 5.19 8.76 11.48 5.38
Dec.
4.80 4.90 12.28 11.40 2.74
Total
115.00 65.83 106.17 115.60 94.15
Annual Average 7.83 8.40 9.58 7.30 8.85 9.63 7.85 8.49
3.3 FISH PROCESSING AND MARKETING
It is estimated that nearly 10% of the total catch from
the lake is eaten fresh (Yeboah, 1974; Maembe, 1991) and
the balance is processed.
The main processing methods continue to be smoking,
salting, sun drying and fermentation.
In general, 18 species of commercial importance are
processed (Table 7). Cylindrical and rectangular Fanti
ovens are extensively used for smoking, with the
cylindrical ones more preferred (58 to 61%). Maembe (1991)
counted 1 881 cylindrical ovens and 1 315 rectangular ones
in 34 villages with 6 993 housing units. Agyenim-Boateng
(1989) recorded 6 569 fish processors in Stratum VII,
while Maembe (1991) recorded 9 328, representing a 42%
increase in two years.
The fishing business has become complex and now is
conducted by what is termed the ‘company’ system. The
company has an investor, a group of fishermen and one or
two fish processors working as a unit by agreement for a
set period (2 years), after which profits accrued are
share in an agreed ratio. The Ntumu system, which is the
marketing strategy, is now well established. It involves
the use of middle-women to facilitate the marketing of the
processed fish, and has developed to become a socioeconomic convenience for the middle-woman and the distant
fish traders on one hand and the middle-women and the
fisherwomen from the fishing villages on the other.
Pricing of fish is based on the season of the year, fish
species and the bargaining skill of the buyer. The initial
price is fixed by the fisherwoman from the village, based
on costs in the week of fishing, processing and
transportation, with a 25–50% mark up.
The fish price per kilogram in 1978 was ¢ 2.06 ($US 0.75
at the time) and in 1992 it was ¢ 300 ($US 0.71). The high
cost of fish today is therefore attributable to inflation,
which is perpetuating itself through high costs of inputs
of production.
In 1991, there were 31 fish markets, of which 11 were
major markets, against 20 in 1975 (Coppola and Agadzi,
1976). The order of importance of these lakeside fish
markets has changed over the years. Whereas the 1975 frame
survey showed that the largest fish market on the lake was
Kwame-krome, followed by Yeji and Kpando-Torkor, the 1991
fish market data on processed fish showed that the Yeji
market was now the largest fish market, followed by Buipe
market and Kpando-Torkor. Kwame-krome market had dropped
to sixth position.
The fish markets are mainly for domestic trade. The Yeji
market attracts fish traders from the Brong Ahafo,
Northern, Upper East, Central, Western, Greater Accra,
Ashanti, Eastern and Volta Regions. Fish from the lake is
also exported to neighbouring countries: Togo, Côte
d'Ivoire and Burkina Faso (Salome-Anshong, 1990).
3.3.1 Production of fuelwood for fish processing
The effects of deforestation have been becoming
increasingly obvious in recent years, making the lot of
the fishing communities even harder. Fishermen have
exploited what is within their reach for fish processing,
and now have to rely on the indigenous tribeswomen to
bring firewood in exchange for fish. The result is the
beginning of a barter trade which is of tremendous
importance to the indigenous tribesfolk, who have no other
work during the farming off-season. In the areas owned by
the Gonja tribe along the lake, the exploitation of
firewood is reserved for the Gonja women. This measure is
providing an extra income to these women. However, the
resultant effect is that settler tribesmen now go to the
lake to cut submerged trees for firewood. This particular
wood, incidentally, is preferred by fish processors and
therefore it has become a lucrative business to cut and
sell the wood, which could have highly significant
implications for the fisheries in the future.
4. RESEARCH AND DEVELOPMENT HISTORY
4.1 APPLIED FISHERY RESEARCH ACTIVITIES
Besides the research activities of the former Volta Lake
Research and Development Programme (LVRDP) and Volta Lake
Research Project (VLRP) of the University of Ghana (1964–
1970), hydrobiological monitoring of the Onchocerciasis
Control Programme (OCP) was started in 1974 by the
Institute of Aquatic Biology and sponsored by the
Onchocerciasis Control Programme of the World Health
Organization.
The (on-going) programme includes the monitoring of
daytime invertebrate drift, night-time drift and analyses
of Surber samples. Some abiotic parameters (Ph,
temperature, turbidity, current speed and river height)
are recorded regularly. The monitoring protocol includes
two-monthly sampling aimed at assessing changes in CPUE,
catches of main fish species on the individual rivers, the
condition of principal fish species of individual rivers
on a monthly basis, length frequency distribution of main
fish species in individual rivers, and, where applicable,
evaluation of the food habits of some important fish
species.
The UNDP/FAO project Integrated Development of Artisanal
Fisheries (IDAF) started in 1989 and, inter alia, research
programmes in biology, fish processing and marketing and
gear development have been undertaken. The project is
currently in its second phase (1992– 1996).
4.2 FISHERY INFRASTRUCTURE
The experience of the fishery complex in Kpando-Torkor has
been incorporated into the plans for the establishment of
the Yeji Community Fisheries Centre (CFC). One of IDAF's
primary objectives since it started in 1989 has been to
facilitate the construction of the CFC. Feasibility
studies have been concluded and a master plan has been
finalized. The first phase of IDAF committed funds for
landfill activities in preparation for the actual
construction to be executed in the second phase (1992–
1996).
In the area of construction of fish processing facilities,
the IDAF Project has already commenced construction of
communal processing facilities in some fishing villages
under the Village Assistance Programme. One was completed
in 1990 in Jaklai village (3 km from Yeji Town) and is
fully operational. The facility comprises a mosquito-proof
storeroom, a chamber for ovens (Chorkor ovens only) and a
third room for washing and preparing fish. Five more units
are planned in other villages.
The IDAF Project has re-incorporated the embryonic cold
storage in its programme for the second phase. In this way
the project intends to install an ice machine with the aim
of promoting the fresh fish trade. Feasibility studies
indicate that the venture would be economic.
A boatbuilding component is attached to the CFC. Even
before the construction of the boatbuilding workshop, a
scheme for providing better tools and machines to the
artisans was initiated. There are plans to install a
slipway for easy launching of boats from the boatyard.
4.3 FISHERY DEVELOPMENT ACTIVITIES
Fishery development activities undertaken include:
*
Fishery complexes
Apart from the Kpando-Torkor complex, the Yeji
complex is to be constructed. An amount of $US 300 000 has
been provided by UNDP for the landfill work on the
proposed site, and $US 4 million will be donated by the
Japanese Government as a grant aid for the construction
itself.
*
Fish processing demonstration programme
The IDAF Project was starting the construction of
village fish processing facilities in six villages. The
Jaklai facility already constructed cost nearly ¢ 177 000
($US 500). The Chorkor oven - which has been rarely used
in the fishing villages - was to be used for extension
work to improve the quality of fish products and save
costs on firewood. One standard double chamber oven with a
complement of 5 trays cost $US 71.
*
Fishery Schools
The Kpando Torkor Fishery School had trained 81
youths (aged between 17 and 21) and 32 young women (aged
between 16 and 21) by 1991. Other fishery schools are the
Mobile Fishery School, with a station at Kpando Torkor
serving 26 settlements, and the Fishery Services Centre,
based at Ampem and serving 35 settlements, both with a
annual budget of $US 32 000.
*
Floating jetty programme
Permanent ramps have proved better than the floating
jetties and were incorporated in the Yeji Complex, at a
cost of $US 28 800.
*
Net Revolving Fund Programme
In the second phase of the IDAF project, and linked
with the Japanese aid grant, the Net Revolving Fund
Programme of $US 1 million will be re-activated.
*
Fishery extension service
The IDAF Project already has already initiated the
development of improved gear to replace outmoded and
illegal gears currently deployed on the lake. Improved
boat construction techniques are also being taught to boat
builders as an on-the-job training activity.
*
Loans to Fishermen
The scheme of providing inputs on credit to trainees
is being revived by the IDAF project. The inputs will be
paid back in instalments.
*
Lakeside fishermen cooperative development programme
The Mobile Training School at Kpando-Torkor and the
Fishery Services Centre at Ampem are actively involved in
the formation of cooperatives. Seven fishery cooperatives
already exist. In order to establish confidence by
entrusting them with the capital necessary for them to
expand their businesses, the IDAF project intends to
create a revolving fund as a means of extending credit to
the various user groups who would have been re-vitalized,
trained and promoted into registered cooperatives by the
Department of Cooperatives.
5. OTHER USES OF THE LAKE
• Water supply and irrigation
The creation of the Head pond at Kpong (24 km downstream
from Akosombo) provided a reliable water supply for the
Akosombo Township, and some parts of the Greater Accra
Region. This facility enabled the establishment of a very
large irrigation project behind the Kpong Head pond in the
Accra plains. From 1992, the Irrigation Development
Authority (IDA) has operated two sprinkler irrigation
projects on the Afram wing of the lake, at Amate and
Dedeso. Currently, almost 35% of the drawdown area is
being cultivated.
• Generation of electricity
With the sustained improvement in the water level in the
reservoir, total energy sales in 1991 were projected to be
5 580 Gwh in addition to the previously installed capacity
already on line, an increase of 1.0% over the 1990 level
of 5 537 Gwh. Revenue from the sale of electricity in 1991
was expected to increase by 13.7% over the 1990 level of ¢
37 200 million ($US 120 million) to ¢ 42 300 million ($US
140 million). The major part of the electricity is sold
and exported (5 540 Gwh) to Togo, Benin and Côte d'Ivoire.
The major internal consumers are Volta Aluminium Company
Limited (VALCO) (2 788 Gwh) and Electricity Corporation of
Ghana (ECG) (1 560 Gwh).
The government has started a rural electrification scheme
in which, by the end of 1992, all regional and district
capitals were to have been connected to the National Grid,
and over 90% of the country was expected to receive power
from Akosombo by 1995. By the year 2000, the coverage was
expected to be 100%.
• Bauxite development project
The total cost of the project was considered high and the
project was deferred.
• Volta Lake Transport
The Volta Lake Transport system now comprises the
following subsystems:
a multi-purpose, break-bulk cargo system for transport of
all commodities (except for mineral oil products) and a
small number of passengers;
a specialized bulk-cargo system for contract transport of
mineral oil products; and
a passenger transport system.
The company's income rose from ¢ 381 million in 1989 to ¢
656.7 million in 1990, with a concomitant rise of
expenditure from ¢ 325 million to ¢ 511.7 million. The
declared cash profit was ¢ 145 million in 1990, compared
with ¢ 56 million in 1989.
• Wildlife
The Digya National Park, with a total area of 31 000 km2,
was established along Volta Lake by Legislative Instrument
710 of September 1991.
• Forestry
The proposed forestry programme for the lake had not
materialized at the time of writing. Selected areas were
to have been forested with fast-growing tree species for
the establishment of a charcoal industry and to help
arrest soil erosion.
6. REFERENCES
Agyenim-Boateng, C.E. 1989. Report on the socio-economic
conditions in the fishing communities in the Yeji area of
Volta Lake. IDAF Technical Report. 90p.
Antwi, L.A.K. 1990 Limno-chemistry of Volta Lake 25 years
after its formation. Inst. of Aquatic Biology, Tech.
Report. 11p.
Baranov, F.I. 1961. Attempt of hydrochemical
classification of the European reservoirs in USSR.
GOSNIORCH, 50: 279–328 [in Russian].
Bazigos, G.P. 1970. Yield indices in inland fisheries with
special reference to Volta Lake. Volta Lake Research and
Development Project, Statistical Studies. Report No
FAO/SF/GHA/10/St.S./3. FAO, Rome. 25p.
Biswas, S. 1966. Ecological studies of phytoplankton in
the newly forming Volta Lake of Ghana. J. W. Afr. Sci.
Assoc., 11: 14–19.
Braimah, L.I. 1989. Observations on fishing gear in the
Yeji part of the Volta Lake. IDAF Technical Report. 20p.
Braimah, L.I. 1990. Handbook of alternative fishing gear
for Volta Lake. IDAF Technical Report. 20p.
Braimah, L.I. 1991. Efficiency tests conducted on newly
designed gear for the Volta Lake. IDAF Technical Report.
16p.
Coppola, S.R., & Agadzi, K. 1976. Frame Surveys at Volta
Lake (Ghana), 1975. Volta Lake Research and Development
Project, Statistical Studies. Report No GHA/71/533/St.S/5.
FAO, Rome. 148p.
Goudswaard, P.C., & Avoke, S.K. 1993. Length frequency of
processed fish in Yeji weekly market. Field Document of
IDAF, project UNDP/FAO GHA/88/004.
Ioeffe, C.I. 1961. Forming of benthos fauna in the USSR
reservoirs and their classification. GOSNIORCH, 50: 341–
381 [in Russian].
Loiselle, P.V. 1972. Preliminary survey of inshore
habitats in Volta Lake. A report prepared for the Volta
Lake Fisheries Research project. Technical Document No 2
of UNDP/FAO project FI:DP/GHA/67/510. FAO, Rome. 122p.
Maembe, T.W. 1991. Report of mission on socio-economics
and marketing in fishing villages dependent on Yeji as a
fish market. IDAF Technical Report. 90p.
Obeng-Asamoah, E.K. 1977. A limnological study of the
Afram arm of Volta Lake. Hydrobiologia, 55: 257–264.
Obeng-Asamoah, E.K. 1984. A limnological evaluation of
Volta Lake. SCOPE/UNDP Sonderband Heft 55: Hamburg. 425–
435.
Ofori-Danson, P.K. 1990. Review of fish fauna in the
Akosombo Gorge area of Volta Lake after 25 years of
impoundment. Tech. Report, Inst. of Aquatic Biology. 13p.
Rajagopal, P.K. 1969. Preliminary observations on the
vertical distribution of plankton in different areas of
Volta Lake. pp. 123–126, in: Obeng, L.E. (ed) Man-made
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University Press.
Salome-Anshong, A. 1990. Status of the current trade in
fish products (fresh, smoked, salted, dried) passing
through Yeji. Report prepared for IDAF. 48p.
Tyurin, P.V. 1962. Influence of water level fluctuation in
reservoirs on the forming of the fish stock. GOSNIORCH,
50: 395–410 [in Russian]
Yamamoto, S. 1991. Species composition in relation to mesh
size. Unpublished IDAF technical report. 5p.
Vanderpuye, C.J. 1984. Fisheries and limnology of Volta
Lake. pp. 261–320, in: Kapetsky, J.M., & Petr, T. (eds)
Status of African reservoir fisheries. CIFA Technical
Paper, No 10.
van der Straten, G. 1990. Report of a pilot survey for
processed fish landing at Yeji -Volta Lake. IDAF Technical
Report. 65p.
van der Straten, G. 1991. Report on the follow-up of the
recommended statistical data collection system and the
organization of the data computerization at Yeji - Volta
Lake. IDAF Technical Report. 32p.
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