The River Niger enters Nigeria from Niger Republic about 162 km north of Kainji Lake. The Sokoto River joins the Niger about 75 km downstream of the border and extends upstream with a broad floodplain for about 387 km (Hughes and Hughes, 1991). Altogether, there are an estimated 470,000 ha of seasonal floodplains on the Niger/Sokoto system.
The upper reaches of the Sokoto and Rima rivers (Fig. 2) are fed by numerous streams and rivers which are usually filled by rain water run-off during the rainy season and dry up during the dry season. These streams and rivers are characterised by narrow width, of not more than 30 metres, shallow depth of 1 – 3 metres, and swift currents at high water level. The river banks usually have a steep slope into the water, and flooding over the banks is not usually a common phenomenon.
Flood ponds are common within the flood basins of most of the major rivers and are usually cut off from the main river channels during periods of low water. The seasonal streams and rivers are also segmented into series of pools in the deeper areas of their channels. Typical of such flood ponds are the Mashe Lakes on the Rima River flood basin near Argungu, while the Baja Lakes along the channel of the River Gaminda and the Fakka/Uwamange series of lakes on the River Gawan Tsamiya channel represent the pools.
These ponds and pools range in area between 10 and 100 hectares of water surface, and as a result of their progressive reduction in surface area and water volume during the dry season, they provide a good concentration of fish for easy harvesting during the periods of lowest water level (FACU, 1989). Most of the pools have low fish production on account of their high turbidity and low fish supply since they are usually overfished prior to the next flood season.
Fig. 2. Map of the Sokoto-Rima river basin.
The income levels of those who fish these water bodies is comparatively low, ranging from about $1.00 to $2.00/day (U.S. dollars) during the poor fishing season and increasing to between $4.00 and $10.00 per day during the peak fishing season*. This is equivalent to catch rates of between 2 – 4 kg and 8 – 20 kg per day respectively. The average catch per fisherman per annum is estimated at 1.5 metric tonnes.
The lower reaches of the Sokoto River are perennial and characterized by wider river beds of about 30 – 100 metres and deeper waters of up to 5 metres. This sector of the river is endowed with extensive flat plains which are flooded during the rainy season. These plains provide good breeding and nursery grounds for fish and also increase the total water surface area, with the attendant boost to the natural productivity of the water bodies.
Some multipurpose reservoirs have been built by harnessing some of the major and minor tributary rivers e.g. Goronyo reservoir (20,000 ha) on the Rima River and Bakolori reservoir (8,000ha) on the main Sokoto River prior to its confluence with the Rima River. Scattered across the plain are small natural lakes, among which are Kware (200ha), Kalmalo (5,000 ha), Natu and Saru lakes.
These categories of water bodies present the largest surface area of water across the Sokoto River and its plains extending from the confluence of the Sokoto River with the River Niger right up to the Rima River. Table 5 presents the surface areas of these various water bodies and their expected fish production. The pools of seasonal rivers and their floodplains have a total surface area of about 496,500 ha. This category is characterized by the seasonality of fishing on account of the fluctuations in the water level. The average concentration of fishermen per square kilometre is lower than that of the River Niger. The catch, although high during the flood season, reduces drastically during the dry season after the mass cropping of fish from stagnant pools of seasonal rivers. However, on account of the large surface area, the total catch is comparatively high (about 34,000 mt/yr.).
* All prices given in this text can be assumed to be 1989–90 prices ($US1.00 = N10.00) unless otherwise stated.
Floodplains of Argungu Local Government Area
In the Argungu area, as well as most parts of the Sokoto-Rima River floodplain area, most active fishing takes place during the dry season (January to April). During the wet season months (May to September) fishermen engage in farming and do fishing part-time.
This local government area is noted for its Fishing Festival which has gained both national and international recognition. The Argungu festival started about 70 years ago, when the Emir of Sokoto, Hussan Dan Muhazu of Sokoto came to Argungu to make peace with the Emir of Argungu after a series of tribal wars between the Kabawas and the Fulanis. To entertain the Emir of Sokoto the Emir of Argungu, Mohammed Sama authorised his people to go into the Rima River to catch fish for the visitor. Thereafter, that day was marked by a fishing festival in Argungu.
At the start of the festival the “Sarkin Ruwa” or Chief of Fishermen pours libations and says some incantations to enhance the fish catch. Afterwards there are usually cultural displays and a competition to determine the most skilful fisherman. The best 30 fishermen are presented with gifts. All the fish caught at the festival, which normally lasts for about 4 days, are bought by the State Government and later these are presented to important dignitaries from all over the country who attend the festival.
The site of the fishing festival is a 1 km by 50 metres stretch along the Sokoto River. During a visit in the month of June, the estimated maximum depth of the river was about 5 metres. The river was fast flowing and turbid. The littoral margin was lined with patches of aquatic vegetation mostly Polygonum, Echinochloa and Nymphaea species. The shoreline was steeply sloping with limited breeding areas for adult fish. However, the Sokoto Rima River at Argungu is located on a flat river bed with the flow almost at ground level and areas of extensive flooding along the valley. The width of the valley is approximately 6 km (as measured along the Natsini/Argungu Road). On either side of the festival area can be observed some flood-ponds which could be developed into breeding and nursery ponds for Tilapia for subsequent release into the festival stretch of the river. Such introduction would encourage an influx of carnivores such as Lates, Heterobranchus, Gymnarchus and Clarias which are highly prized during the festival, since the fisherman with the biggest catch (often ranging from 20 to more than 50 kg) is usually donated a car, together with some cash.
The fishing operation is a well organized business in this area. At the beginning of each fishing season, the “Sarkin Ruwa” fixes a date and all the fishermen move to a particular lake to fish. They continue to move from one lake to another until they come back to the lake where they started. This usually takes between 2 and 4 weeks to accomplish. The “Sarkin Ruwa” has the authority to start or stop fishing in the area. Usually, during the farming season he stops all the fishermen from active fishing until farming activities end. He then informs the Emir of Argungu and initiates real fishing activity. The title of “Sarkin Ruwa” is hereditary in this area. It does not depend on how skilled the fisherman is. Anyone belonging to the Royal Sarkin Ruwa family is free to compete for the post.
Fishing gear used in this area includes clapnets and long lines, unbaited with closely arranged hooks (Mari Mari). clapnets are used during the dry season when the water level is low while the hook and line method can be used during both dry and flood season along the shallow littoral margins of the lakes or floodplain. The use of gillnet is prohibited by the local government in this area. This is to ensure that resources are conserved for the Argungu fishing festival.
The fishing craft most used is the calabash, but the fishermen using castnets prefer to operate from small dugout canoes made from date palm trees. The canoes are about 6 metres long overall, 0.5 metres beam and 0.5 metres deep. They are shaped with a stern piece for seating, but with a straight cut-off bow. The canoes are also used for racing competitions during the fishing festival.
The economics of fishing in this area depend on the season. During the active fishing season a good fisherman can catch about 15 to 20 kg of fish and make about $15 to $20 dollars daily. Occasionally a single Nile perch Lates niloticus or catfish Heterobranchus bidorsalis could weigh between 8 kg and 15 kg and would sell for about $8 to $15 dollars. The cost of a fishing unit, including calabash ($6.00) and clapnet ($19.00), is about $25.00 dollars. It is estimated that during the active fishing season of about 90 days between January and April a good fisherman can earn about $450.00 dollars or about N4,500.00 (Nigerian Naira).
The fish caught are sold fresh to middlemen who move with the fishermen from lake to lake. The fishermen are not involved in any form of processing. The middlemen are responsible for processing and preservation of the fish, usually by smoking and frying, in preparation for the various weekly markets in the area including Argungu market, which is held on Fridays.
Small Reservoirs and Natural Lakes
Fishing activity in these small water bodies is well described in FACU (1989). Fishing is a year-round activity in these bodies of water with the highest intensity of operation occurring during the dry season (i.e. November to April). Fishing effort is usually reduced during the rainy season when fishing operations have to be combined with farming.
In addition to gillnets, the entangling hook, line and clapnets, other fishing gear in use in these water bodies include:
longlines, known locally as “Lingo”. These long lines are used all year round. They are made of hooks (Nos 7 to 16) with the standard line consisting on average of 100 hooks. The twine size of the hook lines varies with the sizes of the hooks while the main (long) line is usually made of No. 6 kuralon line. The hooks are baited with small fish, preferably alive, in order to attract large carnivores.
castnets, locally known as “Brigi” are also in use. These castnets are of a standard design, about 3 – 4 metres long with a spread circumference of 15 – 20 metres. The netting is made of nylon with small mesh sizes of between 38mm and 51mm in 210D/3 twine. Such castnets are widely used in most of the small lakes and reservoirs.
gear combinations fishermen operating in small reservoirs and natural lakes mostly combine longlines with gillnets.
The fishing craft is the prototype plank canoe, designed and built at Yelwa, in Yauri Local Government Area of Sokoto State. This canoe, which is flat-bottomed, usually has the hull constructed out of 5 pieces of specially sawn plank. The bottom sheet consists of one plank wide enough to give a beam of up to 0.9 – 1.0 metre and long enough to give up to 9.0 metre length overall. This plank is shaped at its extremities to provide narrow and pointed stern and bow which, in combination with 2-piece side walls, give the canoe the required sleek and streamlined form for ease of propulsion. The wood joints are sealed with a solution of styrofoam in petrol, which hardens on evaporation of the solvent to an effective glue, and are held in position by iron nails. The major hull supports are the 5 – 6, 150mm wide thwarts in the standard canoe, plus gunwale runners about 50mm wide along the top of each side from bow to stern, which also help to keep the thwarts in position. A well shaped stern-piece is provided for seating the paddler and helmsman, while a flat deck piece is installed, forward of the first thwart, to provide a standing facility for cast-net fishing.
This prototype canoe, made of mahogany (Kharea irorensis) 20 – 25 mm thick, was found to be quite suitable for such fisheries. Sizes depend on the requirements of the particular fishery and range from 3.5 metres upwards to 10 metres for fishing purposes. Larger canoes of this type are also being built for the transportation of goods. The fisheries on small reservoirs and natural lakes mostly utilize canoes of 5.5 metre overall length with a beam amidships of 33cm, and maximum depth of 40 – 45 cm.
Table 6. Estimated fish production along the Niger/Sokoto River floodplain system.
|1.||Small natural lakes and reservoirs||40,000||3||1,200||1.0||1,200|
|2.||Pools of seasonal rivers and floodplains||496,500||2||22,680||1.5||34,020|
|3.||River Niger north of Kainji Lake||87,500||8||7,000||1.8||12,600|
Source: Modified from FACU (1989)
Fish production from small reservoirs and lakes (total surface area of about 400 km2) is about 1,200mt/yr, (Table 6) and the concentration of fishermen is about 3 per km2. Fish production in most of the reservoirs is low on account of their high turbidity and low initial fish supply from stagnant pools of water which are usually overfished prior to the next flood season. In Goronyo and Bakolori reservoirs, for example, fishing is seasonal, with the peak fishing season coinciding with the early flood period (September to November) and the receding flood season (March to May). These reservoirs require stocking with fingerlings of indigenous species to enhance their productivity.
The natural lakes are more productive than the reservoirs, as was evident from observations in the field. Kalmalo Lake for instance has a booming Tilapia and Clarias fishery all year round. Others like Kware and Natu have their peak fishing season but the few full-time fishermen engage in fishing throughout the year.
The catch per fisherman in reservoirs and natural lakes is comparatively low and ranges from 2 – 4 kg per day during the poor fishing season to between 5 – 10 kg during the peak fishing season. The average catch per annum is therefore estimated at 1.0 tonne/fisherman.
The Kaduna River is another major tributary of the Niger. It rises from the Jos Plateau, flows in a north-westerly direction and then southwards to join the Niger downstream of Wuya at Pategi. It covers a distance of about 575 km and drains an area of about 66,300 km2 of diverse topography.
The river is dammed at Shiroro, about 348 km down its course, to form a reservoir with a surface area of about 312 km2. Another dam is currently being proposed at Zungeru about 77 km downstream of Shiroro with a proposed surface area of about 974 km2.
The river can be divided into two topographical zones:
The Upper zone starting from Zungeru town. This area is generally undulating with many rocky hills and rapids.
The Lower Kaduna zone starting from Zungeru town down to the confluence, a distance of about 150 km. This area is characterized by the presence of an extensive floodplain covering a total of about 150,000 ha down to the Niger.
There is limited fishing activity along the upper Kaduna River where the river flows through a hilly terrain with steeply sloping shorelines. Landings of artisanal fishermen examined in December 1990 (NIFFR, 1990) revealed a predominance of Tilapia, Lates, Alestes and Chrysichthys in the catch. Other species of lesser importance include Schilbe, Clarias and Auchenoglanis. A total of about 19 species have been identified in commercial landings at Shiroro Reservoir with Tilapia species dominating the catch two years after impoundment. Seven years after impoundment, Lates niloticus became the dominant species. The predominantly rocky shoreline, coupled with the presence of clupeids in the reservoirs, possibly favoured the development of Lates.
Fishing is more intensive along the lower Kaduna River and its floodplain. The fishing gear include gillnet, castnets, clapnets, hooks and lines and assorted local traps. Fish fences are also used by the Nupe fishermen to trap fish during the retreat of flood waters.
The River Niger north of Kainji Lake, from Yelwa to the border with Niger, is estimated to flood about 88,000 ha of the plain on either side. Below Yelwa, the Niger expands into Kainji Lake and then into Jebba Lake for a distance of about 100 km below Kainji dam. Prior to the creation of Jebba Lake, the portion of the Niger between Kainji and Jebba was characterized by rapids and steeply sloping shore lines without extensive bank overflow. However, from Jebba to the Niger/Benue confluence, a distance of about 300 km, the river frequently overflows its banks forming extensive floodplains on either side whose width of about 15 km upstream reduces to 10 km along the lower 80 km stretch. Altogether there is an estimated total floodplain area of about 385,500 ha in some flood years (Hughes and Hughes, 1990).
Between Idah and Onitsha, there is another extensive floodplain of about 165,000 ha.
The River Benue enters Nigeria from the Cameroon flowing south-west, and has an extensive floodplain for a distance of about 187 km. It varies in width between 3–10 km. Below this, the river is confined within its banks for about 100 km before flowing over the banks again, up to the confluence. There are extensive floodplains throughout the 200 km from Karkurdi to the confluence with widths of about 10 km, mostly along the South bank. Altogether there is an estimated 312,000 ha of floodplain along the River Benue.
The stretch of the River Niger from Jebba to Lokoja covers a distance of about 300 km with an estimated floodplain area of about 385,500 ha. This floodplain includes lakes (e.g. Lake Ndakolowu), swamps and marsh lands. A frame survey conducted in 1985 identified a total of 1,780 fishing boats (of which 503 were mechanized) and 5,193 fishermen, of which 1,780 were boat owners and the rest assistants.
Commercial catch statistics along this stretch obtained in November/December 1985 showed the numerical predominance of Tilapia (25.6%) followed by Synodontis (24.8%) and Labeo (8.3%), Citharinus (6.3%), Schilbe (6%), Mormyrus (5.6%), Bagrus (5.2%), Alestes (4.6%), Gymnarchus (3.3%), Clarias (2.6%), Lates (2.5%), Heterotis (2.2%) and Chrysichthys (1.4%). Other species of lesser economic importance included Auchenoglanis, Clarotes, Malapterurus, Heterobranchus and Distichodus.
Tilapia also dominated the catch in terms of weight making up 20.1%, followed by Synodontis (15.1%), Citharinus (10.9%), Labeo (9.3%), Mormyrus (7.5%), Gynnarchus (7%), Bagrus (6.4%), Lates (6.3%), Clarias (4.7%), Alestes (4.1%) and Heterotis (3.1%). Other species of lesser importance included Chrysichthys, Schilbe, Clarotes, Auchenoglanis, Malapterurus, Heterobranchus and Distichodus. These made up less than 6% of the total landing of 610 kg of fish in the sampled villages. The estimated daily catch per boat along the stretch was 11.3 kg while the estimated total annual fish landing was 4,431.6 mt.
Judging from the order of relative importance of species in the catch, no carnivores being dominant, it could be assumed that the bulk of the catch came from the floodplains rather than the main river channel, supported by the fact that the period of the survey coincided with the flood season. In view of the importance of floodplains to the fish production of this and other river systems in Nigeria, a case study of the floodplain lake (Lake Ndakolowu) located along this stretch of the river will be summarized.
Lake Ndakolowu (also called Lake Tatabu) is a floodplain lake of the River Niger downstream of Jebba Dam. It is located between 9° 12' –9° 14'N and 4°52' –4°58'E, about 24 km from Jebba along the Ilorin - Kaduna road (Fig. 3). The damming of the Niger at Kainji in 1968 and at Jebba in 1983, and the subsequent water control from these dams, resulted in drastic reduction of the floodplains downstream of Jebba Dam up to Lokoja and beyond. One of the most badly affected floodplain lakes was Lake Ndakolowu.
Some interesting studies have been carried out in this area. Its potential for agricultural and fisheries development has been reported on by Mutter (1972b). Awachie (1976) also discussed the fishery potential of the Lake Ndakolowu area. Investigations into the fisheries of this lake were also conducted by the Kainji Lake Research Institute between 1977 and 1979. In 1971 the surface area of the lake was estimated at 9 km2 and by 1977 it was reduced to 6 km2. By 1979 the area was much less than 6 km2 and after the completion of Jebba Dam in 1983 the open water area of the lake was completely obliterated and the lake was reduced to pockets of overgrown swamps.
In April 1988 the lake completely dried up, with terrestrial vegetation covering the entire area, leaving a few ponds here and there. Between April and June 1988 the embankment along the Niger was excavated down to the level of water in the river in order to permit inflow of water, along the 6km channel (Fig. 3), into the lake during the flood. The experiment was successful and in September 1988 the lake was restored with increased fish landings.
The hydrology of the River Niger before and after the construction of the Kainji Dam has been well documented (NEDECO, 1961; FAO, 1973; Zimmermann et.al., 1976; Bidwell, 1976 and Sagua, 1977b). Two distinct floods occur annually, the black and the white flood. Before Kainji Dam the black flood reached the Kainji and Jebba areas around November with a peak flow rate of 2,000 m3/sec. and the white flood arrived in August with a peak flow rate in September/October of 4,000–6,000 m3/sec. Before the dam, the lowest level and discharge rates were between May and July and the highest in September/October with a subsidiary rise between December and February. After the dam, this pattern continued only upstream. Flow was greatly altered downstream due to flood control by the dam authority although, even when outflow is delayed in order to allow the lake to fill, it still reflects the two flood types.
Fig. 3. Lake Ndakolowu and other floodplain pools cut off from the River Niger by the Kainji Dam.
The new flood regime in the middle Niger (Jebba - Lokoja), after the construction of the Kainji and Jebba Dams, has a regulated flow all year round with a reduced white flood and higher flow rates than previously during off-flood periods. The resultant effect of the changed flood regime on Lake Ndakolowu was the silting and gradual obliteration of the lake.
The vegetation cover of the floodplain lake area has been well documented in Daddy et.al. (1989). The open water area of the lake is dominated by Pistia stratiotes, Nymphaea lotus, Lemna paucicostata and Echinochloa stagnina. The permanently moist soils contain Cyperus distans, Echinochloa sp., Phragmites karka, Ipomoea aquatica and Sacciolepis africana. The exposed dry areas due to the complete recession of water for about two decades were colonized by terrestrial vegetation such as Andropogon gayanus, Digitaria sp., and Aspilia africana among others.
The fish species composition of floodplain waters generally depends on the flood regime. Consequently, fish are concentrated in permanent water bodies at low water levels, but disperse further afield over the floodplains during the flood phase. Migration of fish within tropical river systems has been well documented (Motwani, 1970; Welcomme, 1969 and 1975). The major controlling factor is dissolved oxygen concentration. A lower level of dissolved oxygen is observed (Egborge, 1971; Carey, 1971; Welcomme, 1971) at low water than at high water and in floodplain waters than in the main river channels. Consequently species found in floodplain waters are adapted for survival in low dissolved oxygen conditions. The dominant fish family by weight in Lake Ndakolowu in 1977 was the Osteoglossidae, closely followed by the Cichlidae, Clariidae and Gymnarchidae. However, in 1978, the order of dominance changed to Cichlidae, Hepsetidae, Gymnarchidae, Clariidae and Mochokidae. It was interesting to observe that even by number the Hepsetidae ranked high. The appearance of the hepsetids marked an increased incidence of carnivorous species. Otobo (1977) observed that piscivorous centropomids and characids dominated the middle Niger. A critical examination of the catch records revealed that:
Although Lake Ndakolowu was fed by the over-spill of the River Niger at Jebba, the lake and the associated river channel had different dominance orders with respect to their fish species compositions. While the lake was dominated by primary and secondary consumers, the river channel was dominated by the piscivorous species and, even when carnivores came into prominence in the lake in 1978, they were the “stalking” species like Hepsetus as against the “pursuing” species in the river channel such as Lates and Hydrocynus. Furthermore, there was an indication that the gymnarchids, clariids and ophiocephalids were restricted to the lake while the bagrids, cyprinids and citharinids were restricted to the main channel.
In the lake itself some very striking re-arrangements in the dominance order seemed apparent over a two year period. The cichlids and the ophiocephalids retained their positions at the top and bottom respectively; the mochokids showed a decrease in number but the gymnarchids an increase. The most striking change however, was the increase and decrease of the hepsetids and osteoglossids respectively.
Direct estimates of the standing stock in Lake Ndakolowu are not available but weights of fish caught after one week of sampling per month from February to September 1977 and 1978 have been used to estimate the annual catch from the lake. Consequently the collective weight of fish families and/or economically important species was obtained. Furthermore, as the same number of fishing days and gillnet (length and mesh sizes) were used throughout the period of investigation it has been possible, for comparative purposes, to express the catch in “kilograms per unit effort” where this represents the total catch for 7 days per month. Lelek and El-Zarka (1971) used a similar unit of measure. The gillnet fleet used consisted of seven nets each measuring over 30 m × 5 m with mesh sizes of 3.75cm, 5cm, 6.25cm, 7.5cm, 8.75cm, 10cm and 12.5cm (1.5", 2", 2.5", 3", 3.5" 4" and 5").
In 1977 a total of 1,417 fish weighing 382.69 kg were caught while in 1978, a total of 1,564 fishes weighing 219.99 kg were caught. This gives a computed yearly catch estimate of approximately 600 kg from just one fishing boat operating at the rate of only 7 days in a month. In 1977 the average total catch per month during the dry season - corresponding, in the Kainji Lake area, to the “flood phase” - was higher than that of the wet season, “dry phase”. This is the reverse of what has been observed in reservoirs and could perhaps be explained by the fact that, although the fish were more widely dispersed over the floodplain during the flood phase, the total ichthyomass increased considerably due to spawning and this offsets the negative effects of dispersion over a wider area. Conversely, at low water, with migration of the fishes back to the main river channel, there was a significant drop in the total ichthyomass present over the floodplain, if only because the smaller volume of water persisting at this time has a lower overall carrying capacity. Figures obtained for 1978 showed a fall in the number of fish caught during the flood season and a rise in the number caught during the low water season. Despite this the average weight of catch in the dry (flood) season in 1978 surpassed that in the wet, indicating that although fewer fish were caught they were bigger.
A critical examination of the mesh selection revealed that in both years, and for all the families, the most effective (which caught the highest numbers and weight of fish) mesh sizes were 2.5", 3" and 3.5". Selective cropping of fish in Lake Ndakolowu by the judicious use of these three mesh sizes would sustain the fisheries and fishing potential of the lake because the majority of the species caught were mature adults and their capture would not be detrimental to the fishery.
The lake serves three small fishing communities - Tatabu and Tsafa to the west and Bachwa to the east. gillnet, usually of 1.5"–4" mesh, are used by the local fishermen and very rarely are hooks used. Beside these two types of gear the villagers permit no other on the lake. This restriction arises from their belief that for as long as gillnet alone are used the lake will be productive. This belief is associated with a nearby shrine of a water god. Most of the fish caught are smoked in earthen kilns and the regular sale of these fish has transformed Tatabu - a fishing village with a population of less than 5,000 - into one of the few major fish markets along the Jebba to Kaduna road.
Commercial catch statistics obtained in May 1979 (low water season) at five out of the seven fishing stations along the shore of the lake revealed that there were over 60 canoes operating on the lake with a mean catch of about 7 kg of fish per boat per day. Of a total of over 370 kg of fish landed by 54 boats, Tilapia and Sarotherodon topped the list with a total weight of 234 kg, followed by Heterotis with 82 kg. Other species of commercial importance were Clarias sp. with 29 kg and Gymnarchus weighing 11 kg. Updated canoe counts revealed that the lake was capable of yielding over 90 metric tonnes of fish annually.
Commercial catch statistics obtained in April 1988 with catches from pockets of swamps, prior to the resuscitation of the lake with the influx of flood water in August of the same year, revealed the presence of only Oreochromis, Clarias, Heterotis and Channa comprising 55%, 36%, 9% and 0.3% respectively. By October of the same year, after the influx of flood water, the number of species had increased from four to seven and the dominance order also changed with Heterotis dominating the catch by number and weight (48% and 43% respectively) followed by Polypterus with 29% and 39%. Other fish were Oreochromis (3% and 2%) Mormyrops, Channa, Protopterus and Synodontis.
About four fishing stations and 10 boats were recorded in September 1988 (Daddy et.al. 1989). The fish landings had been restored to 7 kg/boat/day as was recorded in 1979 when the lake level was considerably reduced. By June 1990 the order of species dominance in commercial landings had changed with Oreochromis taking the lead in terms of abundance (36%) followed by Clarias (28%), Alestes (9%), Citharinus (7%), Heterotis (8%), Auchenoglanis (3%), Labeo (4%), Synodontis (4%) and Schilbe (0.2%). It is apparent that species succession is still undergoing some changes, but it is expected that the dominance of the tilapia group may never possibly be overtaken by other species.
The importance to the fish production of this floodplain lake of restoring the surface area of Lake Ndakolowu cannot be overemphasized. The booming roadside fish market at Tatabu village, which had disappeared when the lake dried up, has been restored. It is possible that other smaller floodplain lakes along the stretch which has been affected by flood control could be restored in a similar manner. In addition to refilling dried up ponds and swamps by means of a channel, Reed et.al. (1967) attempted to retain water for longer within the floodplain along the middle Niger around Lokoja, by blocking the connecting channel between the swamps and the river with a simple earthen dam and sluice gate.
The philosophy behind this approach was that:
The surface area of the swamp would be increased and perhaps doubled. The increased area would be shallow water covering fertile grassy banks and forests thus leading to increased production of algae, plankton and insects and these would provide rich feeding grounds for most fish species leading to faster growth rates.
The additional flood water available, and also the increased area suitable for young fish to shelter from predators, would increase the percentage survival of juveniles and thus numerically enhance the stocks.
The harvesting of fish could be delayed by a few months and during this time the fish would increase in weight significantly.
In places where an abundant supply of suitable species of fingerlings was available near the affected swamps, these could be netted and transferred alive to inside the controlled areas where they could grow for another six months before being harvested.
Based on the above philosophy, Reed et.al. (1967) carried out two experiments around Lokoja floodplain area using the bunded lagoon approach to increase the surface area of the swamps.
The dams were built during the dry season each with a sluice gate in the centre through which water could enter the swamp during the flood season. As the flood rose, all the bunds were submerged and remained so for several months. The dams were built of clay and in some places old sacks were packed full of mud and used in holding back water. The two dams were stocked naturally and had no additional fingerlings added to them.
As the flood receded, when the level of the water dropped to a few feet above the bund, a fish fence was placed along the top of the dam and the gates screened, to prevent the escape of fish. Fishing in the swamps was prohibited after this. In November, when the level of water dropped to the top of the bund, the sluice gates were closed. The total area of water held back by the two dams was over 100 hectares. This represented an area about twice the normal perennial pools of previous years. The lake created by the dam nearest the river was about six feet above the lowest river level while the second was about ten feet higher than the river level.
About four months later, fish screens were put in place, the sluice gates were opened and the water poured out until the levels were reduced to that of the river. Fishing was then declared open. Over a thousand fishermen with assorted fishing gear took part in the fishing operating in the form of a festival with drumming and celebration. A total of about 15 tonnes of fish was harvested, estimated at about 150 kg per hectare. Most of the fish were small and medium sized as expected, but since all the fish were consumed, it was thought more reasonable for humans to consume the small fish than for predators, the natural beneficiaries, to consume them. Since it is reckoned that the feed conversion ration of predators is about 10:1 (food to flesh), it is better for humans to consume about 100 kg of small fish than 10 kg of a big predator.
The species composition of the catch and production per unit area varied from swamp to swamp. Citharinus dominated one of the swamps nearest the river while predators were common farther away from the river in the shallower areas. The fish production from these bunded swamps was estimated to be about double that from those without bunds. Reed recommended the need for more experiments to determine what factors had the greatest influence on the increased productivity.
While the need for identifying the factors responsible for increased productivity of bunded lagoons cannot be overemphasized in order to select ideal areas for constructing more lagoons, it is believed that the need to identify more sites for construction of such lagoons should be the major area of emphasis. The local fishermen could be guided to adapt the technology to enhance more intensive communal fishing as observed during the experimental fishing trial.
The commercial fisheries of the River Benue between the confluence and Makurdi, where the floodplain is most extensive, were surveyed in 1987. The frame survey conducted in January/February 1987 revealed a total of 2,051 boats along this stretch, of which 478 were mechanized. A total of 4,627 fishermen were identified of which 2,576 were assistants giving an average of about 2 fishermen per boat. The fishermen were settled in 140 villages along both banks, with 71 on the northern bank. An average of about 14 boats were estimated per fishing village.
The catch statistics collected in randomly selected villages along the northern and southern banks revealed average monthly landing of about 283 metric tonnes giving a total estimated annual fish landing of about 3,396 mt. The dominant species in the catch in order of importance were Tilapia, Synodontis, Citharinus, Labeo, Alestes, Auchenoglanis, Chrysichthys, Hydrocynus, Bagrus, Schilbe, Lates, Mormyrus, Clarias, Heterotis and Distichodus comprising about 19.6%, 17.1%, 11.5%, 10.3%, 9.3%, 6.2%, 5.9%, 4.0%, 2.9%, 2.8%, 2.5%, 2.3%, 1.7%, 1.7% and 1.0% respectively. Other species of lesser importance in the catch included Heterobranchus, Clarotes, Cynoglossus and Channa (Ophiocephalus) sp. making up less than 2% by number of the total landings of 2,120 fish. The relative proportion by weight of the catch was 13,5%, 9.2%, 6.9%, 8.0%, 4.7%, 7,0%, 4,2%, 4.0%, 4.6%, 0.8%, 20.9%, 4.1%, 2.5%, 6.3%, 0.8% and 1.1% respectively. The remaining three species made up less than 1% of the estimated total landings of about 498 kg during the survey period. In terms of biomass, Lates niloticus dominated the catch followed by Tilapia, Synodontis, Labeo, Auchenoglanis, Citharinus and Heterotis. The period of the survey coincided with the receding flood suggesting that the bulk of the catch came from the flooded plains.
Beyond Makurdi, the floodplain narrows down to less than 5 km for a distance of over 100 km and then expands from Ibi to more than 5 km width for a further 100 km or more. In 1979 a total of about 357 fishing boats were counted along the 94 km stretch between Makurdi and Tunga giving an average of 3.7 boats per kilometre length of the shore on both banks of the river. When this is compared with a concentration of 10.3 boats per kilometre on the stretch between the confluence and Makurdi, it is clear that fishing activity is more concentrated along the lower 200 km of the river. If the 3.7 boats/km is regarded as the average along the upper stretch of the river from Makurdi to the border it could be concluded that there is a total of about 2,220 boats along the remaining portion of the river estimated at more than 600 km. With a conservative estimate of 1.2 metric tonnes per boat per year (based on an average of 5 kg per boat per day for about 20 fishing days per month) it is estimated that a total fish landing of about 2,664 mt/yr. could be expected from the remaining stretch of the river between Makurdi and the border.
This, added to the estimated 3,396 mt/y between the confluence and Makurdi gives a grand total of estimated landings of about 6,060 mt/yr/for the main course of the River Benue and its floodplains.
In addition to the main stretch of the river, there are many tributary rivers and their floodplains and ponds, such as the Gongola, Katsina Ala, Dep, Mola, Taraba etc. all of which contribute to the fish production of the Benue River system. In the former Gongola State (now Taraba and Adamawa States) there are over 5,000 ha of small natural lakes whose surface areas are virtually doubled during the flood season. These are highly productive water bodies which help to increase the protein intake of the people in these inland States.
Estimates of potential fish yield from the Cross River and its wetlands have been attempted by Moses (1981). Using Welcomme's (1975) formula for quick approximation of possible yields from rivers he arrived at estimates ranging between 7,790 and 17,140 mt per year with a mean of 12,405 tonnes. However, he accepted the lower limit of 7,790 tonnes as the approximate potential yield considering the low fish production of the river (about 10 kg/ha/y).
Moses (1987) also attempted to extrapolate the catch from the Cross River floodplains, based on the influence of the flood regime, and arrived at a mean annual catch of 4,791 tonnes over a period of twelve years (1972–1983).
Statistical frame and catch assessment surveys of the artisanal fisheries were conducted between 1985 and 1986 with the objective of substantiating these theoretical estimates and providing a working data base for the management and control of the fisheries and the population of fishermen. A total of 811 boats and 2,214 fishermen were counted along the eastern shore in 43 fishing camps, 29 fishing villages and one resettlement village (Table 7). Along the western shore a total of 929 boats were counted with 2,665 fishermen giving an average of two to three fishermen per boat for the river stretch.
The estimated total landings along the eastern and western shores of the Cross River during the flood season of June to August 1985, and a combined estimate for the eastern and western shores at the peak of the low water season prior to the onset of the flood in April 1986, is shown in Table 8. The mean of monthly landings for the flood season was about 153mt for the western shore and 216.3mt for the eastern shore giving an overall total for the flood season of 368.9mt. Thus the total landing for the flood season extending between May to October was about 2,213.4 mt, while that of the dry season was estimated at 2,534.4 mt giving a total annual fish landing of about 4,747.8 mt for the freshwater zone of the river.
The above estimates exclude landings along the brackish water areas extending from Calabar creeks on the eastern shore and Oron along the western shore to the confluence towns of Obioko and Effiong Oron on the eastern and western shores respectively. Estimated landings at Calcemco Beach (Calabar Town) in June 1985 gave average monthly landings of 31.2 mt for the flood season. These estimates confirm Moses' (1981) conclusion that the lower figure of 7,790 tonnes is preferable to his upper estimate of 17,140 tonnes. However, in view of the limited number of boats operating along the brackish water area the lower limit of 7,790 tonnes is a good approximation of the total fish landings along this whole river stretch.
The composition of the catch for the two consecutive seasons is shown in Table 9. Chrysichthys made up the bulk of the commercial landings both in June 1985 and April 1986, followed by Clarias and Tilapia in June 1985 and Clarias, Lutjanus and tilapia in April 1986. There was more species diversity in June, possibly as a result of the influx of migratory spawners with the early flood waters, than in April at the peak of the dry season.
Table 7. Distribution of boats and fishermen along the shores of the Cross River in June/ August 1985.
|Type of boat||Total||Size of Crew||Total|
Table 8. Estimated total fish landings along the western (W/S) and eastern (E/S) shores of the Cross River between June and August 1985 and April 1986.
|Name of sampled village||No. of boats sampled per day||No. of boats at frame survey||Total catch||Sum of T/1 – 3||Rf1||G Sum of Rf1||H G(l/p)||I Sum of G(1/p)||J Mean of I||K Monthly total catch|
J ×C (kg)
Key to Notations
D1 – 3 = Days of taking samples
T1 – 3 = Total catch for each day
Rf1 = Raising factor = number of canoes in the village over number of selected canoes
l/p = Inverse probability raising factor = total number of canoes in the minor stratum over total canoes in the selected village
C = Month raising factor = total number of fishing days in the month over number of days of taking samples
Table 9. Catch composition from commercial landings along the Cross River
|Species||June 1985||April 1986||Moses (1979)|
|% No.||% Wt.||No.||Wt. (kg)||Mean|
|% No.||% Wt.||Mean catch|
* Figure represents total catch for family Characidae
** Figure consists of Parachanna (1.2%), Citharinus (5.6%), Ctcenopoma (0.2%), Heterobranchus (6.3%), Xenomystus (0.2%),Crayfish (0.8%), Polydactylus (2.6%), Mullet, Snapper, Sole, Mackerel etc. (15.1%)
1 Here, as elsewhere in this text, this category includes Oreochromis and Sarotherodon.
Moses (1979) gave a more comprehensive checklist of commercial landings, comprising both freshwater and marine species possible caught along the brackish water zones of the Cross River, which were not sampled during the current survey. His data comprise landings, recorded between 1972 and 1975 with tilapias topping the list (Table 9), followed by mormyrids, Clarias and Chrysichthys. Other species recorded by him are shown at the bottom of Table 9.
The mean weights of the four major species identified during the two surveys were higher in June samples than in April, indicative of bigger spawning populations during the flood season. Judging from the relatively large sizes of fish caught by the fishermen during the survey period, the mesh sizes of nets used in fishing were adequate and should not constitute any serious threat to the fishery.
The Anambra River Basin is located between Latitude 5° 55' and 7° 40'N and Longitude 6° 40' and 7° 42'E. It is situated east of the River Niger, into which it empties south of the confluence of the Niger and Benue. The Imo Basin is located south of the Okigwe Hills from where it rises between latitudes 4° 45' and 6° 17'N and longitudes 6° 35' and 8° 10'E.
The Anambra River has a few major tributaries among which are the Rivers Ofu, Okulu, Adada and Mamu. The major tributaries of the Imo River include the Rivers Ibu, Iyiba, Uchu, Anamiri, Iyeachara, Eme and Otamiri. All these tributary rivers are perennial.
The two basins are located in the rain forest zone with adequate rainfall. The rainy season begins in April and lasts for seven months up to October. The inundated soils are composed of clay with a good water retention capacity and hence several flood ponds are left behind after the flood season.
The overflow from the River Niger floods the low lying plain between the Niger and the Anambra rivers. There are an estimated 52 large perennial lakes and ponds on this plain with a total dry season area of about 1,650 ha (Skoup Consultants and Nippon, 1977) giving an average of about 32 ha/pond.
Along the Imo River Basin, the Oguta/Egbema plain is flooded seasonally by overflow from the Niger and Ulasi rivers which flow parallel to each other. Other floodplains exist all along the course of the Imo River.
The Anambra and Imo Rivers have serious navigational problems caused by fallen trees and logs which constitute obstacles to boats. Fishing is possible only in localized areas. Fishing gear used is limited to long-lines, traps, basket-nets and clapnets. gillnet and castnets are used in restricted areas without obstructions. Fishermen frequently use unorthodox fishing methods, such as explosives, Gamalin 20 and other insecticides, to kill fish.
Table 10. Estimated production from some flood ponds within the Anambra/Imo River basin (March – June 1981)
|Name of pond||Estimated size of pond (ha)||Weight of fish landed (kg)||Production per ha (kg)|
The fish production potential of the Anambra/Imo River Basins was estimated at 10,000 mt by the Overseas Development Administration (ODA) for the former East Central State (now Anambra, Enugu, Imo and Abia States). The yield from the rivers is low hence fishermen resort to exploiting the flood ponds.
The former Anambra Imo River Basin Authority engaged in shared cropping of the flood ponds with the Fishermen Cooperatives, who own the ponds, by supplying pumps to bail out water from the ponds. Other inputs supplied included fishing nets, outboard engines and boats. Fish harvested were shared equally with the pond owners. Ojike (pers.com.) supplied information on the productivity of a few of the flood ponds (Table 10).
The production per hectare is comparatively high when compared with the bunded lagoons of the middle Niger which yield about 150kg/ha. This is possibly due to the increased concentration of fish in smaller volumes of water, and also possibly because the estimated surface areas used were calculated after pumping out the water and are therefore not a true reflection of the original surface areas of the ponds.
However, considering the fact that the original river channel was not intensively fished like the Niger and Benue on account of obstacles along its course, the ponds could have higher concentrations of fish than those of the Niger and Benue floodplains. The true production per hectare could be fixed at about one third the observed i.e. about 288.5kg/ha. Even this extrapolated production is relatively high compared with those observed in other African floodplains which were estimated at about 40 – 60 kg/ha/6 months (Welcomme, 1976) i.e. about 80 – 120 kg/ha/yr. The latter production rate is comparable to that estimated by Reed et.al. (1967) for the lower Niger.
The total floodplain area of the Niger/Anambra basin is estimated at 165,000 ha, while that from the apex of the delta to the confluence of the Niger and Benue, at Lokoja, is estimated at 635,000 ha (Mutter, 1973). At a production rate of 80 kg/ha/yr the Anambra floodplain could produce an estimated 13,200 mt of fish a year, while the production for the stretch from the apex of the delta to Lokoja can be put at about 50,800 mt/yr.
The Yobe Basin is drained by many rivers (including the Kano, Hadejia and Jamaa're Bunga and Komadugu Gana) which eventually join to form the Yobe River that flows into Lake Chad. The drainage originates as the Kano and Chillawa Rivers along with their numerous minor tributaries. These two major tributaries meet south of Kano town to give rise to the Hadejia. The river cuts the Hadejia valley on a west-east axis. About 24 km upstream of Gashua town it is joined by the Jamaa're Bunga River which rises on the Jos Plateau.
Above the confluence of the Hadejia and the Jamaa're Bunga the floodplain begins about 127 km upstream on the former and about 100km upstream on the latter. At the confluence, the floodplain reaches a maximum width of 62 km, but quickly contracts to about 5 km for a distance of 135 km downstream (Hughes and Hughes, 1991). This area, which has many inter-locking shallow water courses running parallel to the main river channel from above the confluence to the end of the floodplain, has often been referred to as the inland delta. It has an estimated wetland area of about 337,000 ha with another 89,000 ha along the Hadejia River and 63,000 ha on the Jamaa're Bunga River above the confluence.
Another floodplain about 180 km long and 7 km wide (73,500 ha) occurs on the Komadugu Gana River. From the confluence of the Komadugu and the Yobe downstream there is a small floodplain measuring about 20 km long by 7 km (14,000 ha). After this, no other major wetland occurs on the river until just before it enters Lake Chad where there is an extensive swamp area covering about 48,000 ha. There is a total of about 624,000 ha of seasonal and permanent swamplands on this system.
Within this system, the Hadejia Nguru wetland has been identified as a Ramsar wetland area on account of the seasonal occurrence of migrant birds to the area. It is an internationally protected area under a joint project (The Hadejia Nguru Wetlands Project) between the Nigerian Government and several international organizations including:
The Finnish Association for Nature Conservation (FINNIDA)
International Council for Bird Preservation (ICBP)
International Union for the Conservation of Nature and Natural Resources (IUCN)
Nigerian Conservation Foundation (NCF) and
Royal Society for the Protection of Birds (RSPB).
Several studies have been commissioned within the project area among which are studies on the Hydrology and sustainable resource development (Adams and Hollis, 1987); Economic valuation of wetland benefits (Barbier et.al., 1991); Studies on the fishery-related aspects of the protected area (Matthes, 1990) and several other studies.
Adams and Hollis (1987) have identified the impact of drought and dam construction on the Hadejia - Nguru wetlands. Their model reveals that between 1964 and 1971 over 200,000 ha of the project area were flooded every wet season. From 1972 to 1982 between 100,000 and 200,000 ha were flooded, but since 1983 flooding has covered less than 90,000 ha each year with 1984 having less than 30,000 ha of floods. Their model shows that evaporation from the inundated area and flooded soils represents about 64% of the volume of river inflow while the discharge at Gashua into the Yobe River represents about 24% of the river inflow.
A series of large scale irrigation schemes have been developed on the Komadugu Yobe system including the Kano River Project (KRP) fed by gravity from Tiga Dam. A total of 7,238 ha was under irrigation in the 1985/86 dry season. The Hadejia Valley Project (12,500 ha) is almost completed. There is also the South Chad Irrigation Project (SCIP) which started in the 1960s, using water lifted by pump from Lake Chad, but it has remained dry for some years due to the effect of drought on the lake. It is estimated that if all the schemes under development are fully implemented, flooding will never extend over more than 150,000 ha.
Barbier et.al (1991) in their assessment of the economic importance of the Hadejia Nguru wetlands to the local population identified crop production, fuelwood and fishing as some of the key benefits they provide to the people. The economic analysis indicated that the agriculture, fuelwood and fishing benefits are substantial on both a per hectare basis and in terms of the minimum and maximum amount of flood water required to sustain them. Their present worth are estimated at:
Agriculture ranges between $85 and $128 per hectare
Fishing ranges between $24 and $37 per 10,000 m3 of water (maximum flood inputs)
Fuelwood ranges between $37.50 and $56.5 per 10,000 m3 of water (minimum flood inputs).
In addition to the major economic benefits, there are other significant economic benefits provided by the floodplain system such as livestock grazing and groundwater recharge. Other unquantifiable benefits include recreational, educational, scientific visits and control of bird pests. It is reckoned that the sum total of the additional benefits may actually exceed the estimated returns to floodplain agriculture, fishing and fuelwood.
In view of these findings the authors concluded that the benefits provided by the floodplain cannot be excluded as an opportunity cost of any scheme that diverts water away from the floodplain system.
A comprehensive fishery investigation has been conducted within the area (Matthes, 1990). A total of about 60 fish species were identified during the investigation of which 25 were found to reach weights exceeding 1 kg, while about 35 could reach about 100 g or more. Using the generalized estimates for other African floodplains ranging from 50 – 60 kg/ha/yr the author estimated that 100,000 ha of the floodplain could yeild a fish biomass of 5 – 6,000 mt annually. Assuming that about 10% of this biomass survives the dry season in permanent pools/rivers, it was assumed that about 90% of the production is fished out each year.
Frame survey results revealed that of the 25.855 households which make up the 30 villages, the majority have at least one person fishing all year round. In all, between 14,000 and 18,000 households fish most of the year. Based on the estimates from the 30 villages, out of a total of 150 (20%), it was estimated that there were about 40,000 to 70,000 fishermen in the project area. Given an estimated average number of 50,000 fishermen in the area, each catching about 100 kg/yr, it was estimated that annual production from the area was about 5,000 mt. This gives a total estimated fish production for the whole floodplain area from Hadejia to Lake Chad (624,000 ha) of about 31,200 mt/yr. Production for any particular year however, depends on the extent of flooding.
Fishing gear and methods used included foul-hook lines, fish baskets, clapnets, gillnet, seines, traps and pots adapted from Mali fishermen. Gaff hooks, clapnets and seines are usually used during communal fishing parties and festivals along water bodies in depressions (fadama) or residual pools in riverbeds. Castnets, long lines (baited) and gillnets are used in permanent water bodies by professional fishermen. Mesh sizes used are small, ranging from quarter inch for castnets and traps to 1 – 3 inches for gillnets.
The existing management system is similar to that of the Sokoto Rima basin system where the “Sarkin Ruwa” (Chief Fisherman) is responsible for determining when and where to fish and when to stop fishing as well as the type of equipment to use. Factors responsible for poor catches by fishermen include an increased population of fishermen, persistent drought and upstream development, leading to the desiccation of most of the floodplain areas. These factors have also given rise to size reduction in the catch and the disappearance of some species especially the larger predators such as Lates.
The fishermen in the area are eager to set up autonomous management councils at village level, in order to have full control over the fishing of their waters. They blamed upstream development for diverting or retaining water and releasing it at the wrong times or too much at once. Most part-time fishermen tend to accept the decline in fish yield as inevitable hoping that improved irrigation farming will generate new income. Full-time fishermen on the other hand were upset and would support any action geared towards the preservation of the perennial lakes and pools.
These three rivers originate from the Mandera Mountains on the Cameroon border and flow into Lake Chad. The Ngadda River traverses a large depression containing 31,000 ha of permanent swamp south of Maiduguri (Hughes and Hughes, 1991). From here it flows for about 120 km north east into Lake Chad across a great seasonal floodplain which extends around the southwestern corner of the lake.
The Yedseram flows east of Maiduguri and enters the floodplain 50 km south east of the Ngadda. The El Beid rises in Cameroon and forms the border between Cameroon and Nigeria for 400 km between Madagali and Lake Chad. It has a floodplain over most of that distance.
No information is available on fishing activity within these floodplain areas. The area is, however, known to be intensively grazed as the floods recede. Cattle move into the floodplain from distant areas and also move across the national boundary into Cameroon.
The open water area of Lake Chad is reported to have fluctuated between 1,000,000 and 2,500,000 ha prior to the 1972/73 drought. Between July 1973 and November 1975 the lake level fell to below 250,00 ha (Hughes and Hughes, 1991). There has been a significant increase in flooding during the 1988/89 season leading to a resurgence of the lake area to about 1,000,000 ha (Sagua, 1991). About 27% of the estimated area belongs to Nigeria (270,000 ha). The main floodplain located south and southwest of the southern portion of the lake, within the Nigerian sector, is estimated at about 1,100,000 ha at maximum flood area.
The major inflow into the lake (about 95%) comes from the Logone/Chari system from Chad and the Cameroon. The contribution from the El Beid River is estimated at 2.5% with another 2.5% entering the lake from the Nigerian Rivers Komadugu Yobe, Yedseram, Ngadda and other smaller rivers and streams. The rainfall around the lake area averages about 300 mm/yr while evaporation is estimated at 2,000 mm/yr. The Nigerian side of Lake Chad is characterized by the presence of numerous small islands and swamps.
Hopson (1967) identified over eighty fish species in the lake but since the 1972/73 drought year there has been a considerable reduction in the number of species, leading to a complete disappearance of Lates and Gymnarchus. The dominant fish are currently Clarias and tilapias. Other genera still persisting include Alestes, Bagrus, Labeo, Distichodus, Protopterus, Malapterurus, Synodontis spp., Mormyrus and Hyperopisus bebe.
Fishing communities are located around the lake on the numerous islands. Fishing activities are at their peak during the flood season which extends between September and February. During the farming season most fishermen resort to farming the drawdown area of the lake. Fishing gear used includes gillnet, castnets, traps and lines. No major frame survey of the fishing communities has been reported for the lake. Because of the distance from the fishing settlements to the neighbouring towns such as Baga and Doro, most of the fish caught are either smoked or sundried after cutting into small chunks. Processed fish are packaged in cartons and transported to Maiduguri and the southern cities.
Sagua (1991) gives current fish production estimates for Lake Chad by extrapolation from the quantity of fish marketed in two major market places (Baga Kawa in Nigeria and Blangoua in the Cameroon) with estimated production equivalent to 25% and 75% of the total lake production. In 1986/87 the fresh weight equivalent of processed fish, estimated at four times the processed weight, was 19,380 mt at Baga Kawa. In 1988/89 fish marketed through Baga was 12,108 mt (fresh weight equivalent) while that passing through Blangoua was estimated at 43,270 mt The author recognises that such statistics, derived from road traffic censuses of vehicles conveying fish, are by no means accurate and there is therefore a need for a more accurate study of catch statistics and a frame survey for the lake. It is however, possible to estimate the potential yield from the lake based on the observed mean yield from floodplains of about 60 kg/ha/yr for the observed area of 1,000,000 ha. This puts the potential yield for the lake at 60,000 mt and about the same figure for the floodplain area.
These are described as large shallow, plains, on impermeable clay known in the northern parts of Nigeria as “Fadama”. These wetlands are well developed north of Kano and between Kano and Katsina (Hughes and Hughes, 1991). The area southeast of Katsina is estimated at about 189,000 ha.
Although these wetlands are not associated with rivers and depend only on run-off during the rainy season, it is possible that they might contain fish as a result of upstream migration during periods of heavy flooding, when the pans overflow and the water finds its way into one of the rivers.
It is necessary to establish the area of the perennial pans to identify their suitability for extensive fish culture in this semi-arid region where most reservoirs dry up during the peak of the dry season.
The Ogun (6° 34' to 8° 57'N; 2° 41' to 4° 9' E) and Oshun( 6° 33' to 8° 20'N; 3° 22' to 5° 16' E) River Basins are located in the extreme southwest corner of Nigeria. They both discharge into the Lagos Lagoon before emptying into the Atlantic Ocean. The total surface areas of the two basins are 2,237,000 ha for Ogun and 1,565,400 ha for Oshun. No estimates of the extent of the floodplains have been reported, possibly because of the numerous minor and major tributary rivers that almost overlap each other.
Fishing activity is concentrated along the coastal region and the brackish water swamps and lagoons. Freshwater fisheries are more frequent on the numerous small reservoirs and the major tributary rivers. A total of ten reservoirs with a total surface area of 3,268 ha have been reported (Elliott, 1979) for the Oshun system, mostly for the supply of domestic water and minor irrigation. More reservoirs are still being planned within the two river systems.
No major fisheries investigations have been carried out on these two river systems. A wachie and Wolson (1978) gave a checklist of species common in the two river systems (Table 2) which shows tilapias dominant in both systems. Elliott (1979) tabulated the order of species importance in the major reservoirs within the Oshun basin showing that, in all but one of the reservoirs tilapias dominate, followed by Clarias spp. in five of the ten reservoirs, and Synodontis, Chrysichthys and Heterobranchus in others. In view of the inadequacy of the catch records no estimates of the fishery potential of these river basins have been attempted.
Because the extent of these floodplains has not yet been estimated it is not possible to use Welcomme's (1976) average figures for floodplains to make an estimate of their potential yield. However, since the total area of the basin is known, his lower average figure of 40 kg/ha/year for rivers and floodplains combined could be used to estimate total production for the basin, including the floodplain. Production from the reservoirs could however be relatively higher (about 60 – 80 kg/ha/yr).