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No Thumbnail AvailableProjectMarine fishery resources of Nigeria: A review of exploited fish stocks 1986
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No results found.In recent years there have been several attempts to review the fishery statistical system and the state of the fishery resources of Nigeria. Nobody has found the exercise easy, for there are discrepancies between the ideal planned statistical sampling scheme and the one effectively operated. And, as details on the current system are not available, it is difficult to determine the accuracy or precision of the reported catch figures and to debias them accordingly. In these circumstances, the re still exist discrepancies between reported combined catches of the artisanal and industrial sectors and estimated yield potential of the Nigerian continental shelf. Some workers have tried to use some results of limited studies, partial sampling and isolated productivity values as rules of thumb, hoping that the inshore fisheries are more or less homogeneous and constant, and also that such results obligingly apply to the entire coastline. The trouble is, however, that the Nigeri an marine fisheries are characterized by temporal and spatial variations, and anyone studying them will soon realize the need for more basic data from the various sectors of the fishery. The complexity of the aquatic ecosystem poses a great challenge to natural science. In the first instance, a comprehensive survey of fishing units and exploited multiple species stocks presents a formidable obstacle. It is therefore understandable that fishery biologists investigating the dynamics of coastal ecosystems have to abstract general principles from the interrelationships of the many species. More recent data on activities of artisanal and industrial fleets reveal rather complicated interactions. (...) -
No Thumbnail AvailableProjectMarine Fishery Resources of Liberia: a review of exploited fish stocks 1987
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No results found.Liberia is situated in the southwestern sector of the great bulge of West Africa. It lies between 4°34'N and 6°56'N, and 7°32'W and 9°26'W. It is bordered to the north by Sierra Leone, to the east by the Republic of Guinea and Côte d'Ivoire. The Liberian coast extends about 590 km (370 mi) in a northwest direction from Cape Palmas on the border with Côte d'Ivoire to Robertsport on the border with Sierra Leone. Liberia has an Exclusive Economic Zone of 200 miles. The conti nental shelf is from 16 to 56 km (10–35 mi) wide and the EEZ is about 18 400 km2. The hydrographic regime of Liberian waters is affected by a relatively stable shallow thermocline lying at mid-shelf. The average depth of the thermocline is between 20 and 35 m in most areas of West Africa, but in Liberia and elsewhere in the Bight of Biafra, the thermocline can be as shallow as 12–14 m. The inshore multiple stock fisheries are exploited with a variety of gears (gilln ets, cast-nets, beach-seines, trawls, purse-seines, ringnets, traps and hooks), operated from different artisanal and industrial fishing boats. The artisanal fishery has undergone less development than the industrial fishery. The total annual catch of the artisanal fishery is about 2 000 t, mostly consisting of coastal pelagic species. The total catch of the industrial fleet including imported finfish landed in Liberia ranges from 4 500 to 9 000 t. The total annual catch of shrimp landed in Liberia is now less than 500 t whereas the annual catch of tuna and tuna-like fish is 330–480 t. The results of the 1981 trawl survey undertaken by USSR using R/V BELOGORSK led to the following biomass estimates (in t) of demersal species (ATLANTNIRO, 1981): (...) -
No Thumbnail AvailableProjectMarine Fishery Resources of Cameroon: a review of exploited fish stocks 1987
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No results found.Cameroon is located on the west coast of the wet forested Equatorial Africa. The hydrographic regime of Cameroonian waters is characterized by the relatively stable thermocline, steep temperature gradient and stable oceanographic conditions below the mixed layer throughout the year. The Eastern Tropical Zone (ETZ) of the Gulf of Guinea from Cotonou (Benin) to Cape Lopez (Gabon) is not affected by seasonal upwelling. But even in this sector, the surface water temperatur es are known to fluctuate between 25°C and 30°C. Seasonal changes are due to the effect of the monsoonal wet surface water salinities. The multiple-stock fisheries are exploited by artisanal fishing units and industrial fleets (finfish trawlers and shrimpers). Both dugout and planked canoes of variable sizes are used by the artisanal fishery to operate a number of fishing gears: e.g., (a) drift net (waka-waka); (b) artisanal purse seine (watsha); (c) beach-seines (draw ing chain); (d) cast net (mbunja); (e) conical shrimp nets (ngoto); (f) multifilament bottom-set gillnets (musobo net); and (g) hook and line. The available data are not adequate to enable the use of conventional stock assessment techniques in assessing the yield potential of exploited species on the Cameroonian continental shelf, estuaries and creeks but preliminary estimates of potential yield made in the sixties indicated that the magnitudes were modest, and lower t han the present combined annual catches of the industrial fleet (12 000–20 000 t) and the artisanal annual catches which amount to more than 20 000 t. (...)
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