PART II - SYNTHESES OF INFORMATION ON SELECTED AFRICAN RESERVOIRS (continued)

PARTIE II - SYNTHESES DE L'INFORMATION SUR CERTAINS RESERVOIRS AFRICAINS (continuer)

VOLTA LAKE (GHANA) (continued)

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
7.	Total alkalinity	Little difference between surface and bottom values	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
STR.	Sub- Str.	1970		1975		(%) change
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
STR.	Sub-	1970		1975		% change
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
Year	Canoe	Fishermen	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

¹ Others include Schilbe/Eutropius, Bagrus spp., Ophiocephalus, Ctenopoma and Mormyridae (Data supplied by Fisheries Department, Akosombo)

Table 11. Percentage species occurrence in different months (January–August 1966)

Species	January		February		March		April		May		June		July		August
Species	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
SPECIES	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