|Marine||479||152||No||Quéro, J.-C., J.-C. Hureau, C. Karrer, A. Post and L. Saldanha (eds.), 1990|
|Freshwater||319||45||No||Daget, J., J.-P. Gosse and D.F.E. Thys van den Audenaerde, 1984|
|Conservation||Knowledge of the status of the freshwater fauna is limited. While a full species list is available from the Checklist of Freshwater Fishes of Africa, there has been little attempt to assess the status of Nigeria’s freshwater fishes. A paper on the Conservation of Freshwater Fish Species in Nigeria was published in 1994 (Bankole et al., 1994). Nigeria has many inland waters. Ita et al. (1985) identified over 12.5million ha of inland waters including natural and man-made lakes, reservoirs, flood ponds, flood plains and cattle ponds as well as rivers and streams and the lagoons and creeks of the delta areas. Major river systems and lakes include: the Niger/Benue River system; Anambra River; Ogun River; Oshun River; Kainji Lake; and Lake Chad. Freshwater fishes are threatened by a combination of natural and man-induced activities. Damming of rivers causes habitat changes that are detrimental to fish species. Fish may become stranded, lose their spawning grounds through vegetation clearance or be affected by the dominance of species that can adapt to the new lacustrine environment. The construction of the Kainji Dam caused the loss of 70,000 ha of downstream floodplain (Motwani, 1970), and Lelek and El-Zarka (1973) reported that the annual tonnages of fish catches at Jebba, downstream of the Kainji Dam, dropped from 19.6 in 1967 to 12.2 in 1969. Drought is a particularly serious problem in the northeast in the Nguru wetlands and Chad basin. Fish distribution in Lake Chad was affected by unusually severe droughts in 1972/73 and 1983/84. The droughts led to Clarias species and other hardy species becoming dominant in the fauna. Lake Chad has become divvied into northern and southern basins, with the northern basin being liable to complete desiccation. Draw-down is also a major problem. It has been estimated that 25-30% of the Lake Kainji bottom is exposed annually (Bidwell, 1976). This results in massive mortality of shallow-water invertebrates and sometimes of rooted aquatic plants which provide food and cover for fish, and may affect the spawning of some shore-line species. In Lake Kainji following dam creation there was an increase in the abundance of fish and subsequently in fishing intensity. Uncontrolled fishing finally resulted in the cropping of juvenile fish which was extremely damaging to the fishery (Balogun, 1985). The same was observed at Lake Chad (Stauch, 1978). Bankole et al. (1994) listed 59 threatened species from 29 families for a selection of river systems and lakes. Of these 15 were regarded as rare, 37 as susceptible and seven as intermediate. The intermediate species were not commercially important or rare but were vulnerable to the effects of drought or fishing intensity. Most of the threatened species were from the Niger/Benue system with lesser numbers from Lakes Kainiji and Chad. The conservation of aquatic resources needs urgent attention. It is essential that full environmental impact assessments are undertaken for major water management schemes. Fishing pressure needs to be reduced by registering and licensing fishermen and their craft, by imposition of closed seasons, and by strictly enforced mesh-size regulations (Ita, 1982; Ita et al., 1982, 1983). This should be part of an integrated approach to: 1. Identify all freshwater fish species in Nigeria so that changes in biodiversity can be recorded; 2. locate breeding and nursery grounds of species and, if necessary, protect them from fishing; 3. establish a database to show diversity, distribution and status of the fish fauna; 4. conduct awareness campaigns to enlighten fishermen and the general public regarding the danger to fish populations from habitat mismanagement and overfishing; 5. involve fishermen in the rational exploitation of aquatic resources and in decisions for their regulation and management; 6. restore some of the dried-up swamps and flood plains by means of recanalisation, to link them with their former watercourses , as was done for the Tatabu flood plain in Niger State (Daddy et al., 1988), although in was that do not create new ecological problems. Contact: N.O. Bankole, A.N. Okaeme and J.S.O. Ayeni, National Institute for Freshwater Fisheries Research, P.M.B. 6006, New Bussa, Niger State, NIGERIA.|
|Geography and Climate||
Nigeria has four main topographic areas. There is a hot, humid coastal belt which varies in width between 16 and 90 km and is covered with mangrove forests. Inland from this, there isa tropical rain forest zone which penetrates up to 160 km into the interior. The central plateau of the country is high (2,000 - 2,500 m), relatively dry and covered with open woodland and savanna. The extreme north of the country is semi-desertic and lies within the Sahelian zone.
There are two well-marked seasons during the year. The wet season, and a dry season which lasts from October to April in the north and from November to April in the south. The climate becomes progressively more arid toward the north of the country.
Although Nigeria is predominantly agricultural, there is an active petrochemical industry in the Niger Delta area and industrial development is expanding, particularly in the south. Heavy urbanization along coastal rivers and lagoons, and intensive agriculture for cash crops in some other parts of the country, may give rise to local pollution problems.
Ref. Vanden Bossche, J.-P. and G.M. Bernacsek, 1990
Lakes: during the "Normal Chad" phase, 5,500 sq. km. (25%) of Lake Chad lie within Nigeria. However, during the "Little Chad" phase, the waters of the lake are concentrated entirely within Cameroon and Chad, and the Nigerian portion virtually disappears.
There are numerous (about 100) small lakes scattered throughout the country, totaling about 91 sq. km.
Rivers, floodplains and swamps: the Niger River drainage covers most of the hinterland of Nigeria. Two main arms, the Niger itself (which flows for about 1,300 km through the country) and the Benue (1,440 km long) are joined by several major tributaries such as the Sokoto, the Gongola, the Kaduna and the Anambra Rivers. The main channels of the Niger and Benue Rivers are flanked by extensive floodplains: 3,000 and 1,810 sq. km. respectively, at peak floods.
The main Nigerian tributaries to these rivers also have extensive floodplain systems. Total inland floodplain area in Nigeria reaches 5,150 sq. km. The southern coastal part of Nigeria is drained by a series of shorter rivers, principal among which are the Ogun, the Oshun (267 km) and the Cross Rivers.
Reservoirs: one major reservoir has been formed on the Niger River behind Kainji Dam. Kainji Reservoir covers a maximum area of 1,270 sq. km. There is a large reservoir at Tiga on the Kano River. Other large reservoirs are in project. There are numerous small reservoirs, totalling about 2,750 sq. km. surface area.
Coastal lagoons: there is a very extensive lagoon system running parallel to the coast in western Nigeria. This consists of three main elements: (a) the Badagri Creek which carries excess flood water from the Ouèmè and Oshum Rivers to (b) the Lagos Lagoon, which connects through a series of creeks to (c) the Lekki Lagoon. The whole system covers over 700 sq. km. The Niger Delta, which covers a total of 36,260 sq. km. consists of a network of distributaries up whcih saline waters penetrate for a considerable distance. There are estimated to be over 15,000 sq. km. of swamplands in the delta which are suitable for aquaculture.
Ref. Vanden Bossche, J.-P. and G.M. Bernacsek, 1990