Table 2. Showing the pattern of changes in limnological parameters from pre-impoundment through filling to post-impoundment
Parameter | Pre-Impoundment | Filling | Post-Impoundment | |||
1. | Temperature | Little difference in surface and bottom temperatures | 1. | Bottom temperature dropped to lowest level in 5 months thereafter fluctuated with slight increasing trend to 1967 | ||
2. | Difference between surface and bottom reduced during flood (July–Sept.) and harmattan seasons (Dec.–Feb.) | Same as for filling | ||||
2. | Dissolved oxigen | Little difference between surface and bottom | 1. | First two years hypolimnion was doxygenated later oxygenated during period of thermal overturn | " | |
3. | Transparency | Very low transparency | 1. | Low during the first two years | " | |
2. | Appreciable increase during second 2 years | |||||
3. | Decreases during flood and harmattan seasons | |||||
4. | Phosphorus | Appreciable quantities | 1. | Difference between surface and bottom values widened | " | |
2. | Distributed in the entire water column during the months of flood and the harmattan seasons | |||||
3. | During intervening months present in large quantities in the hypolimnion | |||||
5. | Amonia | Little difference between surface and bottom values | 1. | Difference between top and bottom widened | 1. | Increased difference between top and bottom |
2. | Present throughout water column during flood and harmattan seasons | 2. | Intervening months large quantities in metalimnion | |||
6. | Nitrate | 1. | During the first 2 years of deoxygenation of lake rarely detectable | Present only in traces except du during the months of flood and harmattan | ||
Thereafter present only in traces except during the months of flood and harmattan seasons | ||||||
7. | Total alkalinity | Little difference between surface and bottom values | 1. | Difference widened | ||
2. | Concentration increased | Same as for filling |
Table 3. Estimated values of total fish yield over the Volta Lake
(1964–1979)
Year | Fish yield (output) | Estimated indices (1970=100) | Remarks |
1964 | 3 437 | 8.61 | |
1965 | 8 449 | 21.17 | |
1966 | 22 161 | 55.53 | |
1967 | 40 682 | 101.95 | |
1968 | 50 960 | 127.70 | |
1969 | 61 783 | 154.83 | |
1970 | 39 133 | 100.00 | |
1971 | 39 035 | 99.74 | |
1972 | 36 011 | 92.02 | |
1973 | 35 900 | 91.73 | Statistical estimate |
1974 | 37 300 | 95.31 | " " |
1975 | 41 945 | 107.20 | |
1976 | 40 704 | 104.00 | |
1977 | 38 262 | 97.77 | |
1978 | 37 261 | 95.22 | |
1979 | 39 368 | 100.60 |
Table 4. Fishing pressure index of the important commercial genera (Vanderpuye, 1972)
Species | Stock (%) | Catch (%) | Fishing pressure index |
Lates niloticus spp. | 38.4 | 11.0 | 0.29 |
Tilapia spp. (incl. Sarotherodon) | 6.4 | 19.5 | 3.05 |
Labeo spp. | 12.8 | 9.5 | 0.74 |
Hydrocyon spp. | 4.43 | 3.0 | 0.68 |
Alestes spp. | 11.06 | 18.5 | 1.67 |
Citharinus spp. | 3.02 | 7.5 | 2.40 |
Distichodus spp. | 11.73 | 7.0 | 0.60 |
Others | 12.14 | 24.0 | 0.90 |
Table 5a Total quarterly commercial catch from 1969 to 1972
(Vanderpuye, 1972)
Round | Period | Weight in metric tons |
01 | May 1969–July 1969 | 17 522 |
02 | Aug.1969–Oct. 1969 | 22 927 |
03 | Nov.1969–Jan. 1970 | 11 326 |
04 | Feb.1970–Apr. 1970 | 10 008 |
05 | May 1970–July 1970 | 9 637 |
06 | Aug.1970–Oct. 1970 | 11 280 |
07 | Nov.1970–Jan. 1971 | 8 988 |
08 | Feb.1971–Apr. 1971 | 9 608 |
09 | May 1971–Jul. 1971 | 10 890 |
10 | Aug.1971–Oct. 1971 | 11 797 |
11 | Nov.1971–Jan. 1972 | 7 489 |
12 | Feb.1972–Apr. 1972 | 8 859 |
Table 5b Catch per 93.3 sq.m (1 000 sq.ft) of experimental gillnet fished from 1968 to 1972 (Vanderpuye, 1972)
Round | Period | Catch/93.3 sq.m of experimental gillnet (large mesh sizes only) |
01 | Dec. 1968–Mar. 1969 | .325 |
02 | May 1969–Oct. 1969 | .532 |
03 | Dec. 1969–May 1970 | .351 |
04 | June 1970–Sept. 1970 | .348 |
05 | Oct. 1970–Jan. 1971 | .266 |
06 | Feb. 1971–Apr. 1971 | .262 |
07 | May 1971–Sept. 1971 | .366 |
08 | Sept. 1971–Feb. 1972 | .232 |
Table 6a Regional changes in the number of villages between 1970 and 1975 Frame Surveys - Volta Lake (Coppola and Agadzi, 1977)
STR. | Sub- Str. | Total number of villages | (%) change | ||||
1970 | 1975 | ||||||
1 | 82 | 130 | + 59 | ||||
01 | 40 | 43 | + 8 | ||||
02 | 42 | 87 | +107 | ||||
2 | 188 | 197 | + 5 | ||||
03 | 76 | 90 | + 8 | ||||
04 | 112 | 107 | - 4 | ||||
3 | 229 | 239 | + 4 | ||||
05 | 161 | 176 | + 10 | ||||
06 | 68 | 63 | - 7 | ||||
4 | 263 | 254 | - 3 | ||||
07 | 103 | 85 | - 17 | ||||
08 | 160 | 169 | + 6 | ||||
5 | 152 | 136 | - 11 | ||||
09 | 46 | 48 | + 4 | ||||
10 | 106 | 88 | - 17 | ||||
6 | 133 | 204 | + 53 | ||||
11 | 101 | 161 | + 60 | ||||
12 | 32 | 43 | + 34 | ||||
7 | 169 | 202 | + 20 | ||||
13 | 87 | 107 | + 23 | ||||
14 | 82 | 95 | + 16 | ||||
8 | 59 | 117 | + 98 | ||||
15 | 31 | 61 | + 96 | ||||
16 | 28 | 56 | +100 | ||||
TOTAL: | 1259 | 1479 | + 16 |
Table 6b Regional changes in the number of canoes between 1970 and 1975 Frame Surveys - Volta Lake (Coppola and Agadzi, 1977)
STR. | Sub- | Total number of Canoes | % change | ||||
1970 | 1975 | ||||||
1 | 1622 | 2634 | + 62 | ||||
01 | 882 | 1168 | + 32 | ||||
02 | 740 | 1466 | + 98 | ||||
2 | 1822 | 1793 | - 2 | ||||
03 | 931 | 1153 | + 24 | ||||
04 | 891 | 640 | - 28 | ||||
3 | 1695 | 2001 | + 18 | ||||
05 | 1014 | 1379 | + 36 | ||||
06 | 681 | 622 | - 9 | ||||
4 | 2087 | 1916 | - 8 | ||||
07 | 694 | 538 | - 22 | ||||
08 | 1393 | 1378 | - 1 | ||||
5 | 1308 | 1058 | - 19 | ||||
09 | 426 | 356 | - 16 | ||||
10 | 882 | 702 | - 20 | ||||
6 | 1201 | 1245 | + 4 | ||||
11 | 860 | 990 | + 15 | ||||
12 | 341 | 255 | - 25 | ||||
7 | 1738 | 1913 | + 10 | ||||
13 | 807 | 938 | + 16 | ||||
14 | 931 | 975 | + 5 | ||||
8 | 601 | 1254 | +109 | ||||
15 | 332 | 678 | +104 | ||||
16 | 269 | 576 | +114 | ||||
TOTAL: | 12074 | 13814 | + 14 |
Table 7. Average total number of input items used per day over time - Volta Lake (Coppola and Agadzi, 1977)
Year | Canoe | Fishermen | Gears | |||
Gillnets | Castnets | Lines | Traps and others | |||
1970 | 9 308 | 10 905 | 56 921 | 323 | 9 504 | 15 993 |
1971 | 9 113 | 9 899 | 61 497 | 418 | 7 982 | 4 109 |
1972 | 9 237 | 11 298 | 67 340 | 911 | 6 684 | 2 228 |
1976 | 10 2121 | 12 472 | 61 107 | 367 | 10 472 | 434 |
1 Total estimates obtained by using seasonality trends
Table 8. Annual value of commercial catch - Volta Lake
Year | Total landings Kg FWE2 | Average mean price (Cedis/kg) 1st stage of transaction | Estimated total landed value (¢) | Total earnings per UFO3 (¢) |
1974 | 37 300 000 | 0.46 | 17 158 000 | 1 906.44 |
1976 | 40 704 000 | 1.05 | 42 741 300 | 4 749.03 |
1978 | 37 261 000 | 2.06 | 76 847 660 | 8 338.63 |
2 FWE = Fresh weight equivalent
3 UFO = Fishing activity by a fisherman/fishermen in canoe plus a set of constructed fishing gears and other fishing equipment
Table 9. Percent species occurrence in different months (January–April and November–December 1965)
January | February | March | April | November | December | |||||||
No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | |
Alestes spp. | 872 | 49.07 | 378 | 26.36 | 908 | 78.80 | 185 | 53.78 | - | - | - | - |
Lates | 92 | 5.18 | 4 | 0.28 | - | - | - | - | 3 | 0.89 | 75 | 6.70 |
Labeo spp. | 103 | 5.80 | 232 | 16.18 | 65 | 5.67 | 41 | 11.92 | 2 | 0.55 | 9 | 0.80 |
Hydrocynus | 197 | 11.09 | 26 | 1.81 | - | - | - | - | 1 | 0.27 | 10 | 0.89 |
Barbus spp. | 5 | 0.28 | - | - | - | - | - | - | - | - | - | - |
Bagrus spp. | 2 | 0.11 | - | - | - | - | - | - | - | - | - | - |
Tilapia spp. | 4 | 0.23 | - | - | 2 | 0.17 | - | - | 55 | 16.37 | 463 | 44.38 |
Citharinus Cith. | 1 | 0.06 | - | - | - | - | - | - | - | - | - | - |
Clarias | 3 | 0.17 | 2 | 0.14 | 51 | 4.45 | - | - | - | - | 4 | 0.36 |
Distichodus | 1 | 0.06 | 169 | 11.79 | 23 | 2.01 | 10 | 2.90 | 22 | 6.55 | 4 | 0.36 |
Heterotis | - | - | - | - | 1 | 0.09 | - | - | - | - | - | - |
Other spp.1 | 497 | 27.95 | 623 | 43.33 | 101 | 8.81 | 108 | 31.40 | - | - | - | - |
Chrysichthys | - | - | - | - | - | - | - | - | 253 | 75.37 | 550 | 49.15 |
Auchenoglanis | - | - | - | - | - | - | - | - | - | - | 4 | 0.36 |
1 777 | 1 434 | 1 146 | 344 | 336 | 1 119 |
1 Other spp. include: Synodontis, Ctnopoma, Hepsetus, Hemichromis, etc.
Table 10. Experimental fish catches in Volta Lake
(January–April 1965)
January | February | March | April | |||||
Total No. | Total weight | Total No. | Total weight | Total No. | Total weight | Total No. | Total weight | |
Lates niloticus | 92 | 8 846 | 1 | 227 | - | - | - | - |
Labeo senegalensis | 63 | 8 527 | 197 | 21 818 | 59 | 7 757 | 41 | 8 164 |
L. coubie | 35 | 11 930 | 28 | 7 983 | 1 | 227 | 1 | 680 |
Distichodus | 1 | 454 | 169 | 15 694 | 23 | 2 540 | 10 | 1 406 |
Hydrocynus spp. | 187 | 38 328 | 26 | 7 484 | - | - | - | - |
Alestes nurse | 708 | 39 235 | 266 | 24 267 | 481 | 55 474 | 183 | 15 422 |
A. dentex | 134 | 22 816 | 66 | 11 113 | 391 | 31 751 | 2 | 454 |
A. macrolepidotus | 20 | 3 674 | 48 | 8 301 | 31 | 4 536 | - | - |
Synodontis spp. | 5 | 1 588 | - | - | - | - | - | - |
Bagrus doemac | 2 | 3 175 | - | - | - | - | - | - |
Clarias spp. | 3 | 3 175 | 2 | 2 722 | 52 | 85 285 | - | - |
Citharinus | 1 | 227 | - | - | - | - | - | - |
Tilapia galilaea | 3 | 907 | - | - | - | - | - | - |
T. nilotica | 1 | 454 | - | - | 1 | 363 | - | - |
T. zillii | - | - | - | - | 1 | 227 | - | - |
Heterotis niloticus | - | - | - | - | 1 | 6 380 | - | - |
Others1 | 500 | 63 504 | 643 | 73 074 | 101 | 27 442 | 107 | 23 476 |
Table 11. Percentage species occurrence in different months (January–August 1966)
Species | January | February | March | April | May | June | July | August | ||||||||
No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | |
Chrisichthys spp. | 204 | 30.68 | 124 | 54.39 | 29 | 60.41 | 334 | 86.75 | 361 | 80.04 | 433 | 77.18 | 191 | 79.90 | 91 | 71.65 |
Alestes spp. | 10 | 1.50 | 1 | 0.44 | - | - | - | - | 24 | 5.32 | 3 | 0.53 | - | - | - | - |
Distichodus spp. | 10 | 1.50 | - | - | 1 | 2.08 | 6 | 1.56 | 10 | 2.22 | 26 | 4.64 | 4 | 1.63 | 1 | 0.79 |
Lates niloticus | 22 | 3.31 | 13 | 5.70 | - | - | - | - | - | - | 1 | 0.18 | - | - | - | - |
Tilapia spp. | 64 | 9.63 | 36 | 15.79 | 11 | 22.92 | 31 | 8.05 | 22 | 4.88 | 60 | 10.70 | 9 | 3.79 | 23 | 18.11 |
Other spp. | 355 | 53.38 | 54 | 23.68 | 7 | 14.59 | 14 | 3.64 | 34 | 7.54 | 38 | 6.77 | 35 | 14.64 | 12 | 9.45 |
Data compiled from the records of the Fisheries Department, Akosombo
Other ssp. include Synodontis (majority): Schilbe/Eutropius, Hydrocynus, Bagrus spp., Ophiocephalus, Ctnopoma and Mormyridae
Table 12. Percentage species occurrence in different months (January–August 1966)
(From Wuddah, 1967)
SPECIES | JANUARY | FEBRUARY | MARCH | APRIL | MAY | JUNE | JULY | AUGUST | ||||||||
No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | No. | % | |
Chrysichthys spp. | 217 | 21.70 | 134 | 56.07 | 188 | 36.37 | 377 | 53.25 | 472 | 63.36 | 236 | 50.11 | 188 | 79.66 | 65 | 36.93 |
Synodontis spp. | 530 | 53.00 | 6 | 2.51 | 121 | 23.40 | 57 | 8.05 | 17 | 2.28 | 9 | 1.91 | 6 | 2.54 | 38 | 21.59 |
Tilapia spp. | 108 | 10.80 | 84 | 35.15 | 104 | 20.12 | 80 | 11.30 | 36 | 4.83 | 24 | 5.10 | 9 | 3.81 | 18 | 10.23 |
Schilbe/Eutropius | 53 | 5.30 | - | - | 29 | 5.61 | 78 | 11.02 | 63 | 8.46 | 9 | 1.91 | 25 | 10.59 | 12 | 6.82 |
Ctenopoma | 7 | 0.70 | - | - | 7 | 1.35 | 36 | 5.08 | 33 | 4.43 | 126 | 26.75 | - | - | 10 | 5.68 |
Hemichromis | 3 | 0.30 | 2 | 0.84 | 8 | 1.55 | 27 | 3.81 | 66 | 8.86 | 21 | 4.46 | 1 | 0.43 | 10 | 5.68 |
Alestes spp. | 18 | 1.80 | 1 | 0.42 | 18 | 3.48 | 27 | 3.81 | 20 | 2.68 | 9 | 1.91 | - | - | 6 | 3.41 |
Distichodus spp. | 15 | 1.50 | - | - | 9 | 1.74 | 6 | 0.85 | 14 | 1.88 | 17 | 3.61 | 4 | 1.69 | - | - |
Labeo spp. | 2 | 0.20 | - | - | 9 | 1.74 | 1 | 0.14 | 9 | 1.21 | 7 | 1.49 | - | - | 6 | 3.41 |
Lates spp. | 22 | 2.20 | 9 | 3.78 | 1 | 0.19 | 1 | 0.14 | - | - | - | - | - | - | - | - |
Polypterus | - | - | - | - | 4 | 0.77 | 3 | 0.42 | 2 | 0.27 | 4 | 0.85 | 1 | 0.43 | 6 | 3.41 |
Auchenoglanis | - | - | - | - | 2 | 0.39 | - | - | 2 | 0.27 | 1 | 0.20 | - | - | 1 | 0.57 |
Others spp. | 25 | 2.50 | 3 | 1.25 | 17 | 3.29 | 15 | 2.13 | 11 | 1.47 | 8 | 1.70 | 2 | 0.85 | 4 | 2.27 |
Total: | 1,000 | 239 | 517 | 708 | 745 | 471 | 236 | 176 |
Table 13. Species composition of the littoral zone overall expressed as a percent weight (:less than 0.1 percent)
Species | Percent weight |
Pellonula afzeliusi | 1.4 |
Mormyrus hasselquistii | : |
Mormyrops deliciosus | 0.2 |
Gnathonemus senegalensis | 0.5 |
G. pictus | 0.2 |
G. niger | : |
Gymnarchus niloticus | 1.1 |
Heterotis niloticus | 1.1 |
Hydrocyon brevis | : |
Alestes macrolepidotus | 0.5 |
A. nurse | 0.2 |
A. baremoze | : |
A. leuciscus | : |
Distichodus rostratus | 4.1 |
Paradistichodus dimidiatus | : |
Citharinus latus | : |
Labeo coubie | 1.4 |
L. pseudocoubie | 2.1 |
L. senegalensis | : |
Barbus macrops | 0.4 |
B. sublineatus | 1.8 |
B. hypsolepis | : |
B. leonensis | 0.7 |
Auchenoglanis occidentalis | 1.2 |
Chrysichthys auratus | 7.5 |
C. furcatus | 0.8 |
C. velifer | 18.3 |
C. walkeri | 1.4 |
Bagrus bayad | : |
Schilbe mystus | : |
Eutropius niloticus | : |
Synodontis membranaceus | 0.6 |
S. filamentosus | 0.3 |
S. gambiensis | : |
S. schall | 0.1 |
S. sorex | 0.2 |
S. nigrita | 6.8 |
Clarias anguillaris | : |
C. lazera | 0.8 |
Malapterurus electricus | 2.2 |
Epiplatys bifasciatus A | : |
E. spilargyreius | 0.2 |
Aplocheilichthys normani | 0.9 |
Lates niloticus | 2.8 |
Hemichromis fasciatus A | 1.7 |
H. bimaculatus | 4.0 |
Chromidotilapia SAV | 1.4 |
Tilapia zillii | 1.2 |
Tilapia SAV | 0.9 |
T. galileae | 7.0 |
T. nilotica | 13.9 |
Leptotilapia irvinei | : |
Ctnopoma kingsleyae | 0.1 |
Parophiocephalus obscurus | 2.1 |
Kribia nana chevalieri | : |
Nematogobius maindroni | 0.1 |
Tetradon fabaka | : |
Polypterus senegalus | 6.0 |