9. ANALYSIS OF CATCH PER UNIT EFFORT DATA

9.1 The Sherbro Division
9.2 The Senegal/Gambia area

9.1 The Sherbro Division

Data obtained from three different sources were compared by the group (Table 7). The first series (first column) of data were obtained from the annual reports of the Sierra Leone Fisheries Division. The second set were taken from the report of the Third Session of the CECAF Working Party on Resources Evaluation, Rome 1976. The third series is that of the Ivorian fleet operating in the Sherbro Division.

The high Ivorian CPUE may have two causes. It may be partly due to higher horsepower engines (400 HP) and may also partly be due to local trawlers underexporting their catches or discarding low valued fishes. It is also noted that the effort units are not directly comparable because the Sierra Leonean effort is expressed in days out at sea while the Ivorian effort is given in hours dragging.

The group was unable to estimate the total catch made in the Sherbro Division because of the complete lack of data from the Soviet fleet operating on the Sierra Leone continental shelf as well as vessels operating from Monrovia. As regards the Ivorian fleet, the group felt that the catch and effort data for the early years do not reflect exactly the stock abundance because of progressive changes in discarding practices. The catch and effort of the last three years (1974-1976) may reflect the current abundance of the stocks since the fleet do not discard any fish. More information on the evolution of catches per unit effort can be found in Appendix 10.

Although the fishing effort in this division has increased with the entry of Senegalese, Soviet, Liberian and Ghanaian fleets, the CPUE on the whole has not shown any marked decrease. It is possible that the stocks are not excessively fished as yet, though the increase in apparent efficiency resulting from learning and reduction in discards has certainly masked the actual decrease in stock abundance.

9.2 The Senegal/Gambia area

Evaluation of fish stocks of the Senegambia area is not easy because of the following problems:

(i) Seasonal migration of fish from Mauritania to Guinea Bissau

(ii) A very active artisanal component (about 6 000 canoes) contributing to about two thirds of the total demersal fish catch

(iii) Participation of foreign vessels in the fishery, performances of which are not well documented

(iv) Considerable quantity of discards at sea; data on discards are also not available

(v) Successive changes in the fishing pattern with the fleet shifting effort from one target species (shrimp) to others (finfish).

Year	Sierra Leonea Kg/day fishing	CECAFb Kg/day at sea	Ivory Coastc Kg/h (400 HP)
1960
1961
1962	1249
1963	1214
1964	1100	1950
1965	1330	1450
1966	1600	1830	204
1967	1248	2370	-
1968	1436	1460	267
1969	1245	1770	236
1970	1171	2290	193
1971	1063	2560	234
1972	1074	134O	225
1973		1220	192
1974		1670	246
1975			235
1976			278

Note: Italian vessels operating from Freetown have 250 HP engines while Ivorian vessels operating on the Sherbro Division have 400 HP engines

Pagellus coupei -

An estimation of the discards has been made for P. coupei by comparing the length frequencies of catches made by research and commercial vessels operating at the same area and season. This study indicates that about 30-40 percent of P. coupei catch are discarded during the fishing season. Selectivity studies conducted on P. coupei shows that if fishermen abide by mesh regulation in force, this problem would be solved without much loss to the fishery. In the north zone P. coupei is more exploited by canoes. In the southern zone, trawlers, particularly the larger vessels with 1 000-1 500 HP engines, exploit P. coupei more than canoes. Between 1973 and 1976, the catch of this species (discards included) increased from 50° to 2 000 metric tons per annum for the southern zone. In the northern area, during the same period, trawlers caught (discards included) between 200 and 300 metric tons per annum while the canoes catch has been estimated at between 1 000 and 1 500 tons. The yield decreased from about 600 kg per day (for a standardized 250 HP trawler) in 1973 to about 300 kg in 1976.

Pseudupeneus prayensis -

The red mullet was exploited traditionally before 1965 but no investigations were conducted on it. Between 1965 and 1970, its exploitation was practically stopped. In 1971, with the arrival from the Mediterranean of 10-12 vessels specifically designed for catching red mullet, the exploitation of this species expanded rapidly. This was the beginning of a diversification period during which there was also rapid increase in the landings. It is possible that before this period the hard bottom grounds have been exploited seasonally (April to June) by Italian vessels, the size and the catch of which remain however unknown.

Analysis of available data show that landings at the port of Dakar increased from about 200 to 750 tons from 1971 to 1976.

Other species -

For the other species landed, the interpretation of the CPUE should be done with care. It is likely that because of changes in target species the specific variations in CPUE do not always correctly represent the variations in abundance. Appendix 9 further discusses these evaluations.