3. RESULTS OF THE FISH SURVEY WORK

3.1 Fish abundance and distribution Togo - Cameroon
3.2 Fish abundance and distribution Equatorial Guinea - Congo
3.3 Allocation of fish resources on EEZ's

The records of fishing operations are shown in Appendix III and the processed results from the length measurements in Appendix IV.

3.1 Fish abundance and distribution Togo - Cameroon

Figs. 4 and 5 show the distribution of small pelagic and demersal fish from Togo to Cameroon. An assessment of biomass within the borders of investigation in the region gives 190,000 tonnes of pelagic and 117,000 tonnes of demersal fish i.e. a total of ~310,000 tonnes of fish of which abt 60% consist of small pelagic. The surveyed area is practically the shelf area from 50 to 200 m depth which was the aim of the survey to cover in this northern part.

Table 2. Distribution of catches by main families in and by bottom and pelagic trawl respectively in the area Togo to Cameroon in August 1981.

Catch grouping:	1-9 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
GEAR : DEMERSAL NO OF HAULS : 26
PRIACANTHIDAE	7	1	0	1	0	35	38.5	24
SPARIDAE	10	8	0	0	0	69	15.1	19
ARIOMMIDAE	2	3	1	0	0	23	32.7	14
CENTRACANTHIDAE	2	3	0	0	0	19	19.6	7
SHRIMPS	4	0	1	0	0	19	15.4	5
SHARKS	1	1	0	0	0	8	25.5	4
SQUIDS	12	1	0	0	0	50	4.1	4
TRICHIURIDAE	3	1	0	0	0	15	9.3	3
CARANGIDAE	8	0	0	0	0	31	3.6	2
CONGRIDAE	0	1	0	0	0	4	24.0	2
POMADASYIDAE	6	0	0	0	0	23	4.8	2
RAYS	7	0	0	0	0	27	4.4	2
SERANIDAE	1	1	0	0	0	8	14.1	2
TRIGLIDAE	3	1	0	0	0	15	6.8	2
ALBULIDAE	2	0	0	0	0	8	6.1	1
BROTULIDAE	1	1	0	0	0	8	9.1	1
CLUPEIDAE	3	0	0	0	0	12	3.1	1
JELLYFISH	0	1	0	0	0	4	10.8	1
SCIAENIDAE	3	0	0	0	0	12	2.9	1
SPHYRAENIDAE	2	0	0	0	0	8	4.2	1
Other fish	-	-	-	-	-	-	2.7	4
TOTAL	3	12	6	1	0	85	55.3	100
GEAR : PELAGIC NO OF HAULS : 3
ARIOMMIDAE	0	1	0	0	0	33	17.0	35
CLUPEIDAE	1	0	0	0	0	33	9.0	18
SCOMBRIDAE	2	0	0	0	0	67	2.4	10
SYNODONTIDAE	2	0	0	0	0	67	1.4	6
BALISTIDAE	1	0	0	0	0	33	1.7	4
CARANGIDAE	1	0	0	0	0	33	1.0	2
TRICHIURIDAE	1	0	0	0	0	33	1.0	2
Other fish	-		-	-	-	-	3.8	23
TOTAL	1	2	0	0	0	100	16.3	100

Table 2 shows the distribution of the catches by main families and by bottom and pelagic trawl separately. The main object of the trawling carried out is to identify the targets detected by the acoustic system. The catch distribution of species in the total number of trawl hauls carried out in a region is thus a combined effect of the distribution of species in situ and the aimed trawling which gives a highly non-random sampling. Table 2 shows that of 26 bottom trawl hauls only one gave catches of more than 200 kg/hour, indicating a relatively low density of demersal fish. 64% of the total catch is made up of species from the families Priacanthidae, Sparidae, Ariommidae and Centracanthidae. The dominating species are Priacanthus arenatus, Dentex angolensis, D. congoensis, Ariomma bondi and Spicara alta.

Only 3 pelagic trawl hauls were made in the region, indicating the low presence of pelagic resources. The mean catch was 16.3 kg/hour and Ariomma bondi, Sardinella maderensis and Scomberomorus tritor were the species with highest presence.

Analysis of variance in acoustic biomass estimates is encumbered with a lot of methodological problems, but one can assume that the relative sampling error will increase with decreasing densities of fish. In areas with very scattered fish distribution the relative accuracy will be lower both in the acoustic system and in the judgements made by the scientist interpreting the echo-traces.

Figs. 4 and 5 show that most of the investigated part of the shelf holds fish resources, but in very scattered densities. The mean density for the covered area is 39 tonnes/nm² , the equivalent mean integrator output is 2.9 mm per nm steamed and at this level the precision of the acoustic system is low. As can be seen from the figures almost all of fish resources were found in a widely distributed but very scattered pattern, and this makes it difficult to split between pelagic and demersal resources in the daily judging of the records from the acoustic system. Hence one should not put too much reliance on the above given biomass figures. They indicate more an order of magnitude of the resources than absolute estimates.

Fig. 4. Pelagic fish distribution Togo - Cameroon, 7-20 Aug. 1981.

Fig. 5. Distribution of other fish Togo - Cameroon, 7-20 Aug. 1981.

3.2 Fish abundance and distribution Equatorial Guinea - Congo

The distribution of pelagic and demersal fish in the region is given in Figs. 6 and 7 respectively. The biomass estimates within the investigated area are 360,000 tonnes of pelagic and 130,000 tonnes of demersal fish resources. This gives a total of 490,000 tonnes of fish of which abt 70% is classified as pelagic. Approximately 2360 nm² of the shallow part of the shelf is not covered in the survey, and if one assumes the same density as in the covered part of the shelf, one should add 90,000 tonnes of fish. This gives an estimated grand total of 580,000 tonnes of fish. The mean density is 39 tonnes/nm² and thus same as in the northern part. As can be seen from Fig. 6 parts of the pelagic resources form aggregated patterns and can thus easily be distinguished from the echo-traces of the demersal resources. But large areas are at the same time covered with low densities of small pelagic fish. The reservations taken for the estimates in the northern part of the survey (see 3.1) applies for the southern part as well. 86% of the total catch in the bottom trawl was from the families Sparidae, Carangidae and Lutjanidae (Table 3) among which Dentex congoensis, D. barnardi, Sparus caeruleostictus, Decapterus rhonchus and Lutjanus agennes were the most prominent species.

Fig. 6. Pelagic fish distribution Eq. Guinea - Congo, 20 Aug. - 3 Sept. 1981.

Fig. 7. Distribution of other fish Eq. Guinea - Congo, 20 Aug. - 3 Sept. 1981.

The mean catch for all 17 bottom trawl hauls was 222 kg/hour. This is four times higher than in the northern part of the survey (see 3.1) but still far below the catch figures in the northern CECAF region where the mean bottom trawl catch during the "Fridtjof Nansen" surveys in May and in September was 1500 kg/hour (from STRØMME et al. 1982).

The pelagic trawl catches (Table 3) were dominated by the families Clupeidae (45%) and Carangidae (20%), mainly of the species Sardinella aurita, S. maderensis, Alectis alexandrinus and Decapterus rhonchus. The mean catch in the pelagic trawl was 142 kg/hour, again considerably higher than in the northern part of the survey, but far below the values in the northern CECAF region (960 kg/hour, from STRØMME et al. 1982),

Table 3. Distribution of catches by main families and by bottom and pelagic trawl respectively in the area Equatorial Guinea - Congo in August 1981.

Catch grouping:	1-9 kg/h	10-49 kg/h	50-199 kg/h	200-499 kg/h	500 kg/h	% incidence in total no of hauls	Mean catch	% of total catch
GEAR : DEMERSAL NO OF HAULS : 17
SPARIDAE	3	4	3	0	2	71	214.1	68
CARANGIDAE	5	1	2	1	0	53	42.6	10
LUTJANIDAE	1	0	3	0	0	24	71.8	8
Other fish							30.9	14
TOTAL	1	5	4	2	2	82	221.5	100
GEAR : PELAGIC NO OF HAULS : 20
CLUPEDIAE	1	0	1	1	1	20	318.4	45
CARANGIDAE	4	0	0	2	0	30	93.4	20
GONASTOMIADE	0	0	0	1	0	5	420.0	15
JELLYFISH	0	0	0	1	0	5	200.0	7
MYCTOPHIDAE	0	1	1	0	0	10	63.4	5
STROMATEIDAE	0	0	1	0	0	5	60.0	2
TRICHIURIDAE	0	2	0	0	0	10	27.0	2
BREGMACEROTIDAE	0	1	0	0	0	5	39.0	1
LUTJANIDAE	0	1	0	0	0	5	16.5	1
MISCELLANEOUS	2	0	0	0	0	10	7.9	1
SCOMBRIDAE	3	1	0	0	0	20	7.6	1
SPHYRAENIDAE	1	1	0	0	0	10	7.5	1
SYNODONTIDAE	0	1	0	0	0	5	13.0	1
Other fish							0.8	0
TOTAL	3	3	4	3	1	70	142.0	100

3.3 Allocation of fish resources on EEZ's

Table 4. Biomass estimates allocated to EEZ's (1000 tonnes)

Country	Pelagic	Demersal	Sum	Density (tonnes/nn2)	Estimate for shallow unsurveyed area	Estimated Grand total
Togo-Benin	14	5	19	22	14	33
Nigeria	55	105	160	33
Cameroon & Fernando Poo	120	5	125	61
Equatorial Guinea	7	7	14	12	0	14
Gabon	310	120	430	45	90	520
Congo	40	-	40	23	10	50
Pagulu	-	2	2			2
Sao Tome	-	14	14			14
Principe	4	4	8			8
Total Togo-Cameroon	190	120	310	39	-
Total Eq. Guin. -Congo	360	130	490	39	90	580

Table 4 shows the estimates of demersal and pelagic fish on the covered part of the shelf, and estimates on biomass in the shallow unsurveyed area, all allocated to the exclusive economic zones. The general cautions on interpreting the estimates should be kept in mind (See 3.1). The main findings for the various countries are:

Togo and Benin

It is not meaningful on basis of the data available to this report to do calculations on biomass estimates for Togo and Benin separately. Both countries have a small shelf and are also expected to hold much of the resources in common. It is therefore more reasonable to split the resources on basis of the area of the shelf. 40% and 60% of the total estimate will then be allocated to Togo and Benin respectively. In absolute figures this gives for Togo 6,000 tonnes of pelagic, 2,000 tonnes of demersal and 6,000 tonnes in the unsurveyed area. The estimated total for Togo is thus 14,000 tonnes of fish. The figures for Benin are 8,000 tonnes of pelagic, 3,000 tonnes of demersal and 8,000 tonnes in the unsurveyed area. The total estimate for Benin is 19,000 tonnes. The pelagic recordings are very scattered on the shelf off Togo and Benin and no pelagic species were prominent in the catches. Four bottom trawl hauls were carried out in the area and Dactylopterus volitans together with various sparids were prominent.

Nigeria

The estimates in Nigerian waters are 55,000 tonnes of pelagic and 106,000 tonnes of demersal fish resources in the covered 50-200 m bottom depth zone. Based on the daily judgings of the echo-traces about 40% of the biomass in the covered zone is classified as pelagic fish.

This is not reflected in the trawl catches as only one pelagic trawl haul was carried out in the area, and then only small quantities of trigger fish and cardinal fish (Synagrops). were caught. In the 14 bottom trawl hauls carried out off Nigeria the horse mackerels and scads (Carangidae) were found present in 6 catches and the clupeids in 2 catches. Among these groups the catch per hour were in no case more than 10 kg. This could indicate that the pelagic share in the total estimate is quite overestimated. The catch distribution of the bottom trawl hauls off Nigeria is as follows (kg/hour):

Catch grouping (kg/hour)	0	1-9	10-49	50-199	200-499	>500
Number of hauls	1	0	8	4	1

The mean catch in the 50-200 m depth zone is 76 kg/hour and the important families are Priacanthidae (31%), Sparidae (15%), Ariommidae (9%) and shrimps (7%). Shrimps were caught in 4 catches with a mean catch of 18 kg/hour when present.

Cameroon and Fernando Poo

The estimates for the surveyed area off Cameroon and Fernando Poo are 120,000 tonnes of pelagic and 6,000 tonnes of demersal fish, i.e. a total of 130,000 tonnes. Of this about 30,000 tonnes are allocated to Fernando Poo. The uncovered shallow parts in Cameroon are estimated to hold 150,000 tonnes of fish. The prominent families in the catches around Fernando Poo are Arommidae (37%, only one haul), Sparidae (27%, 3 hauls) and Centracanthidae (15%, two hauls). The mean of 5 hauls is 54 kg/hour.

Three bottom trawl hauls were carried out in Cameroon waters, and the mean catch was 26 kg/hour, mainly sparids. Sardinella maderensis was caught in one pelagic haul, but in small quantities only (9 kg/hour). The resources of clupeids and carangids seem rather scarce.

Equatorial Guinea

The pelagic resources are estimated to 7,000 and the demersal to 7,000 tonnes of fish. Practically the whole shelf was covered and gives thus a total estimate of 14,000 tonnes of fish. Three pelagic and four bottom trawl hauls were carried out and the mean catches were 44 and 49 kg/hour respectively. The mean density calculated from the acoustic system was 12 tonnes/nm² . This is the lowest density found in the region covered by the survey.

Gabon

The surveyed part of the shelf off Gabon is estimated to hold 310,000 tonnes of pelagic and 120,000 tonnes of demersal or semi-demersal fish. The estimate for the unsurveyed part of the shelf is 90,000 tonnes of fish. This gives then a total of 520,000 tonnes of fish off Gabon. 60% of the biomass in the surveyed area is classified as pelagic fish. 13 pelagic hauls were carried out and the sardinellas Sardinella aurita and S. maderensis comprise 48% of the total catch with a mean catch of 318 kg/hour when present (4 hauls). The carangids amount to 21% of the catch in the pelagic hauls and were present in 6 hauls and then with a mean catch of 93 kg/hour. The mean catch of fish in all 13 pelagic hauls was 204 kg/hour. 13 hauls were carried out with the bottom trawl and the most dominating families and their catch data were:

	Number of hauls present	Mean catch when present	% of catch in all hauls
Sparidae	8	297 kg/hour	71
Carangidae	6	63 kg/hour	12
Sciaenidae	2	49 kg/hour	6

The mean density was 45 tonnes/nm² , estimated by the acoustic system.

Congo

The biomass estimates off Congo are 40,000 tonnes of fish, all classified as pelagic resources. Almost the whole shelf was covered during the survey, only 10,000 tonnes should be added for the uncovered parts. This gives then a total estimate of 50,000 tonnes for the whole shelf. Only one trawl haul was carried out in the area, and this will in no way give a picture of the species in the area. It seems reasonable that the fishes off Congo belong to the same community as off Gabon. Thus the catches obtained in Gabon could cast some light on the species distribution in Congo as well.

Pagulu, Sao Tome and Principe

Only brief examinations were carried out outside the islands but based on this the biomass estimates were as follows (1000 tonnes):

	Pelagic	Demersal	Total
Pagulu	-	2	2
Sao Tome	-	14	14
Principe	4	4	8

Five hauls were carried out around the islands. Of these the three pelagic hauls gave no catch and the two bottom trawl hauls gave 41 and 270 kg/hour respectively of mainly snappers (Lutjanus agennes) and various seabreams (Sparidae).