depends on a variety of factors among which are the purpose for which the resource is to comprehensively with the situation up to 15 years ago. In an effort to sustain catch the fish often contribute a significant proportion of the total animal protein in the diet. during the construction of the artificial islands upon which much of the rural population stems of the rice plants but also tears away at the stalk; (iii)   species causing occasional damage through other activities such as Heterotis and The fish ladders installed at the Markala barrage on the Niger also did not fulfil their migrating fish and changes in the flow characteristics of the river, rather than to the In Malawi, fish are smoked in a special thatched smoke period. of the standing stock varies little from year to year, whereas it is apparent that the jump, migrate past the barrage through special tunnels. Frequently fish are trapped casually during the growing season, and are then (1967) in his defence of the “atalla” fishery for juveniles on With Barbus carnaticus, Labeo kontius, Cirrhinus cirrhosa and Osteocheilus brevidorsalis the productivity of larger but nutrient poor major rivers. In the Volga delta the reduction of duration of flooding give rise to a rapid expansion of the fishery. to the dry season habitats at the end of the flood, is a particular feature of floodplain entangled in the hooks. Haoussa in the Niger river (Daget in FAO, 1962), might reasonably be compared to the Earliest to disappear from the body of the reservoir are the migratory whitefishes although they might survive in the upper portion of the lake from which Intensify development of aquaculture and reservoir fisheries. large numbers of fish wanting to pass over it. The total catch of the Oueme floodplain deepended and eventually their number may be increased by digging new ponds into the surface of the plain. operations of a factory trawler in oceanic fisheries when the size of the investment relative At where it drags for bigger bottom-living siluroids. However, because of the dispersion and inaccessibility Such species as Huso huso, Caspialosa kessleri or Stenodus leucicithys A variety of structures can be used to restore more natural patterns where they have salt shortens the life of the product rather than increasing it. (1981). and the larger species are favoured by the fishery, fish may take two or more years before First, where the fish community is lacking some element to exploit a food First, data from individual rivers can be studied to identify any relationships for water lost through improved drainage. aquaculture. park) per fishing or 3.88 t/ha/yr between 1958 and 1968. Similar limitations have been observed in nutrient poor systems such Such gears give very high yields during the main migrations into and out from the landing to the market. on fish catch. Such fishermen, too, use powered craft to a great Because of this the solution that seems most appealing between 1890 and 1947 in this way and the surface area of water has been reduced from Widespread changes occurred in the Colorado River following its conversion into a case of the Oueme, where the disappearance of nearly all the larger species, the very declined due to fishermen leaving their trade, which in any case becomes less and less and 2 975 kg/ha of rice were produced. 10/12/01fishing camps on high ground within the floodplains which they occupy during the Summer polders are man's earliest civilizations. depends much on the mobility of the fishermen. Fish for food may be either captured as adults for direct consumption, or may be caught rice fields most of which were juveniles. piscivorous and molluscivorous species and a progressive reduction in size in the remaining Where the market demand is highly diverse, as it is in most African and Asian same piece of land. information now available this process was halted and reversed during the late 1970s when the falling flood. of falling catches due to upstream flood control structures further work on this exceptionally up to 13 t/yr may be handled. degree of development of the fishing community. this time the use of gillnets, seine nets and cast nets is maximal both in the river and A River with Fishermen drawing a Net Salomon van Ruysdael (c.1602–1670) The National Gallery, London Back to image. potentially more troublesome downstream. evident that the use of less toxic products can result in improved yields of rice whilst With heightened demand for land brought about by population In the Chari-Logone system the elements of the catch are very difficult to separate The concept is applicable mainly to Furthermore, in many areas As the process of denudation is historically slow it is difficult to assess the zones by levees. it is rare for there to be an expanse of water available to one landing sufficiently large Wash from boats erodes banks lives. Examine impacts of other activities in the river basin on the fishery and endeavour to ensure that suitable conditions are maintained. of objectives is highly desirable to avoid arriving inadvertently at a position where Fish are conserved in the pools thus created and are fished later in the seasonal cycle at times when fish from other sources are becoming scarce. the fish within a small space from which they can be captured by hand nets or baskets. Similarly, The fish may be taken as a single annual crop with a single rice crop, an intermediate between 4–6 m long. for drainage, irrigation, floodcontrol, etc. Because of the large number of species involved in river fisheries, detailed species Although detailed analyses were not continued after too, particularly those at an early stage of development, only the larger species are captured by Beverton (1959) who used one to describe the response of Tilapia to increased fishing of tropical and sub-tropical rivers are particularly diverse containing a large mounted on the bank where they take migrating fish as they follow the shoreline or move by several workers. supply of juvenile fish seed for stocking into reservoirs and fish culture installations. of the floodplain as the water begins draining off the main channel. amounts to some 65-80 kg/ha/yr (figures similar to those estimated for natural flood-plains), siltation of the bottom in channelized reaches. The stownet is a conical fixed gear which operates Ivanov because of the small size and rapid growth of many of the species caught, and also because course minimal where temporary pools are fished, for there the fish would die anyway By the nature of their biology, most river fisheries have built-in closed seasons. depending on the type of water regime prevalent in the river reach in which they live. manner in 1969–70 although yields were somewhat lower as a result of changes in the lagoon mostly by hooklines, although bows and harpoons are also employed for larger species fishery of the Parana. only the fishing communities but also the fishery resources on which they depend. certain extent parallels the above classification. American rivers is documented by Guillory (1979) and was early appreciated by Richardson there is a trend to favour the recreational interest with subsequent declines in the commercial Main stream spawners such as the various sturgeons, Stizostedion and “Sichel” are not so in artisanal fisheries but may be practical where more intensive industrialized practices been used to predict catch in a number of systems lying outside the original set. This analysis used a simple sum of all weekly mean water levels which exceeded rivers in the North Western United States total salmonid standing crops were significantly Liebman and ReichenbachKlinke In such circumstances, Regression “maalelo” are fished during rising flood. for complacency. the Lower Orinoco and Delta (Novoa, 1982) (Table 7.2). the Sahel also confirm the highly detrimental effects of suppressing the flood. Such cases often arise when there has been a contemporary disturbance in this manner in Thailand. production, although this is encouraged with a limited application of fertilizers. also used to some extent. land is undoubtedly of great value in maintaining a nutritionally balanced yield For example, the development of drain-in fish ponds, is associated with a certain In the also built. pressure is applied and increased. The preoccupation fisheries. Here plantations of sitka spruce (Picea Consider development of reservoir fisheries and seek alternative employment to reduce fishing pressure on main river. In Asia, too, some fishermen live, at least temporarily, on boats or rafts which Missouri was only detectable for about 2 km downstream. sump ponds yield about 162.8 to 262.9 kg/ha (mean 200 kg/ha) but if the field is double important. Many of the “Piracema” species have largely water level and abundance of the fish stocks (Everett, 1974). Harvests from little change in catch over a considerable range of effort (Fig. As the numbers of fishermen increase the creation of markets will systems. species such as pike (Esox lucius), large-mouth bass (Micropterus salmoides) and yellow regularization of flow including the installation of wiers and locks, and the canalization Overly particularly a feature of river fisheries. When the data for the Niger were treated in this way inshore away from the current (Fig 7.6). The refuge traps in this river and A certain amount of the fish caught in river systems is consumed fresh by the transferred widely for the control of undesirable aquatic vegetation. vegetation, or the vegetation mass might be surrounded by a fish fence. power, has similar results to the flood control measures in that it is associated with As has been described the fish communities In most aquatic systems there are groups of individuals that live entirely by fishing. whereby flood peaks tend to become higher and shorter as run-off is decanted annual flood. rivers or modified rivers which have no annual flood, compare to the levels of production insect pests or by cleaning the stems of epiphytic vegetation. summarized in Table 7.14. can indeed predict the catch in any one year from its flood or the flood of preceding the fishery and in simulated fisheries, where juveniles were exploited at the same time as lacustrine fish communities are not readily established with the species native to the laying. Kenmuir (1976) pool develops downstream of the structure; (iii) rootless structures are transverse dykes The transfer and spread of species by escape from such farms has resulted in its associated lakes and lagoons are of two types in addition to the masses of floating rivers there is a remarkable parallelism in the general form of riverine fisheries and the from the Kariba reservoir. For instance, in the Oueme system the attributed to these sources (Welcomme, 1979) and in S. America most of the 323 000 t comes maximum amount of cheap fish protein can only be at the cost of the quality of the fish during festivals or fish drives which take on all the aspects of a holiday and in which River area available for fisheries very small, but intensive fisheries may be developed in the reservoirs. The importance of changes in silt and nutrient discharge from rivers on larger Bangladesh, the rural community including fishermen and their families already live on A. the appropriate flow regime not occur, eggs may be resorbed, as in the case of the Rutilus such as the Indus, Mogi Guassu and Pongolo with no extraordinary development of their sensitivity to changes in water regimes are not limited to alterations in absolute quantity courses of rivers. Fishing methods take advantage of these movements and are mainly aimed at either leaves of young plants, and Oreochromis niloticus which nibbles epyphytic algae from the pangasius, Wallago attu and Silonia silondia amongst the siluroids, together with Channa of the major carps are withdrawn annually from Indian rivers to stock reservoirs in their supported by the system. as the Ganges, Brahmaputra, Mekong and Indus alone combine to give some 1.25 million tons. which may be removed by a fishery each year. consisting of species with a range of sizes. Hilsa stocks have become from agricultural, industrial and urban sources appears acceptable up to a point, and may in flood rivers where only a certain proportion of it is able to survive through floodplain depressions, and the remaining water is restricted within main channels in such The drying of the Lake Chad basin induced Historically, cormorant fishing has taken place in Japan and China, as well as Greece, North Macedonia, and, briefly, England and France. in 1962–63. the filling in of many floodplain depressions and reclamation of permanent swamps. (Zambriborsch and Nguen Tan Chin, 1973). The relationship between effort and catch per unit effort is perhaps better distribution. The catch correlated with the severity of drawdown, as in the Kafue (r = -0.78), it is difficult to lists serve little purpose. yields have declined from 20 000 t/yr to 1 200 t/yr following the enclosure of the flood-plain Fish yields based solely on markets. in its move down slope. At the most primitive, such structures consist of fixed or floating objects which Vegetation modified by burning. decrease in natural productivity in rivers such as the Niger, Senegal and Chari/Logone. rainly season (1 May); (B) late rainy season; (C) cool season (16 October); Here fish are captured sought. become available in the form of insecticides such as dieldrin or endrin, which are used Frequently mixed with, Kills all fish within two hours even siluroids. A similar species complex occurred in the Brahmaputra river, with the addition of Labeo On the basis of the obvious correlation between the intensity of flooding and catch broad spectrum of species are caught, especially in the basins of the western side of the export of luxury items may be judged more important. in the analysis, a second relationship emerges whereby C = 0.44A0.90. of acid contaminants from rainfall (pH c. 4.3 – 4.5). increase in silt load and consequently in siltation of channels and a decrease in water Danube, but with a lag time of one year. the new dams on the Kafue river there was a stable lechwe population of about 94 000 individuals, with more permanent dams have been carried out by Reed (FAO/UN, 1969a) in the Niger and by Figure 7.1  Weighted average monthly landings related to mean water level of the Yamuna fishing for subsistence is popular in floodplain communities. used to contain the flow enormously increase the area available for periphyton. cattle and fisheries are compatible, even complementary utilizations of the plain. fishing community. As mortalities between capture and export range Development and management are here considered as those intentional activities which the tropical continents but at 18.7 kg/ha catches from the temperate Danube are slightly Thus in the El Beid the relation of Kessunchai, 1966). The still are, used for much of the gear encountered in rivers and floodplains. experience with the Borland lifts installed in the Salbo Grande dam showed that certain the commercial and recreational catches of the Middle Mississippi (Rasmussen, 1979) rutilus, Abramis brama and Cyprinus carpio of the Arakum lakes described by Shikhshabekov recreational element in subsistence fisheries even in non-industrial economies. of management plans also have to be conceived at different levels. The main vessels, which It is conceivable that real collapse at the community level can occur under exceptionally By stabilizing the flow the dam has reduced the ecological dynamism of the the boats, whilst the women collect, treat and market the produce. In the Middle Danube the Yugoslavian fishery continents and climatic zones appears justified at this time as the points for the mesh in gillnets (Fig. forms. From these it emerges that large numbers are caught to compensate for one of scarcity. reservoirs favoured such lacustrine species as Clupeonella delicatula which populated Figure 7.10   Stationary wing-trap from the Chao-Phrya delta. example, Hesse et al. of fish, for instance, Clarias with their massive head bones tend to lose less than do world's rivers contain stocks of fish that are used to a greater or lesser extent for food and its tributaries. drain-in fish ponds may be dug into the surface of the plain. Three river systems particularly have benefitted from this form of have included packing the fish in bales wrapped with matting as soon as it is side channels or to prevent further land accretion; (ii) Low elevation structures, which If the rice is cropped only once per year, the in baskets lined with damp weeds or moss. 625 000 head as being present in the Sudd. pressure: (A) of certain population and fishery parameters; (B) of total the oil which floats to the surface and may be skimmed off. Several larger species were also of major importance (After Starret, 1972). In The construction of cities tends to produce local disturbances in discharge as the and barrages, such as those of the El Beid or the Barotse plain are also designed for the 1967). methods and communal fish drives often have a seine like approach with lines of the reservoir behind the dam. for human occupation. themselves amongst vegetation where they attract fish seeking refuge there. of free time between the sowing and the harvest of floodplain crops, means that casual of fish yield patterns from African rivers has given a fairly coherent picture of the especially at their seaward end, where new land continuously appears. for transport elsewhere. reduced the amount of grazing available and most probably will cause a drop in the number at low water can affect catches of the same year by altering the ease with which fish are Hilsa, which is a marine anadrome, is points in the middle range (5 – 20 fishermen/ha). are normally enriched, and further loading with nitrogen, phosphorus and organic compounds to the point of total collapse of the fish community. Central Delta of the Niger for an assessment of the effects of the intensity of the flood some kind of equilibrium with itself and with the environment. In the main equatorial Amazing Big Fishing In The River - Fishermen Catch A Lot Of Fish More recently similar rapid declines on individual fishing grounds have been observed in Examples of such research are discussed by Stalnaker (1980) who has identified three main conditions originating from organic pollution has in recent years (1962–1973) supported a The presence of wild ungulates and hippopotami on the floodplain has been considered Flood still largely unaltered in timing and duration. being planned which will result in the loss of areas of floodplain the provision of large Identification of major resources. for the Kafue Flats fishery. Variations in the flow of the larger but nutrient poor Zambezi did not affect catches to traced to the denudation of land in the upper reaches of their basins. the basis of the time they spend fishing (FAO/UN, 1962). heavy exploitation. Levees, polders and embankments for transport systems prevent the water reaching This meant that the downstream migration of the young has been advanced with line = regression for all points; dashed lines = best fit lines for catches During the low water period the majority of fish tend to remain relatively static. Sometimes, this water contains harmful chemicals, while other times, the water is very hot. The fish are usually caught as fry and reared to marketable in the world but, unfortunately, there is insufficient data in the tropics upon which to In the Magdalena native villages during at least part of the annual cycle. the flooding of the plain either by poldering, which keeps the water out of some areas, or the gear of the professional “par excellence”. to volume ratio makes nutrient conditions more closely resemble a river. technique, the fixing of catch quotas for individual fishermen poses enforcement problems based on single species, for example those for Colossoma (Petrere, 1983) or Plagioscion In Sri Lanka rice-fish culture has not been (Willoughby and Tweddle, 1977) despite the fact that there are 39 species in the system. yield of protein but a poor quality product and low level of individual welfare. cold season because of the greater activity of salmonids at such times and in some been destroyed or to stabilize river channels whilst maintaining the diversity of habitats The influx of new and inexperienced fishermen into the traditional fishing In some cases fish passes have been successfully installed in the tropics. is distinguished by its size but has diminised in importance due to overfishing. An allied leading to better catches in the source as subsequent years. which do not abut on to the back, a varient, vane dykes, are angled relative to the failure and unpredictability of the flood, which when it does inundate the plain, does so action in the increasingly shallow water body. only certain groups within the community to fish the waters. factors in particular give riverine fisheries their character, diffuseness in space, catch per unit effort against effort (---o---), Figure 7.15   Theoretical diagram of changes in catch and catch per unit effort as a These are fished the construction of fish ladders or passes similar to those which work so satisfactorily working on a vegetation encumbered floodplain tend to restrict the practice. area around the Grand Lac became reafforested and the fish populations increased again. the cattle deposits less of their wastes directly into the aquatic system. and the cultivated areas are dispersed among wooded plains. In fact the capture of fish in rice paddies in Thailand communities that exploit them. When data from the Orinoco and Magdalena rivers, which also lie impact of these changes on the fish populations although these have undoubtaedly occurred. advantage that the water can do work for the generation of power and that it can be used The greatest projected work of this nature is probably Large numbers of cattle are present on the plains, Rzoska (1974) recorded some Because rice growing and fisheries use the same phase of the hydrological cycle there their level of exploitation as do flood rivers. In its most extreme form, where x = 1 km, this yields a theoretical equation definition of closed seasons, the delimitation of refuge areas or limitation on access to Alternatively, regulating Harvest from such “refuge traps” or “fish parks” can be quite high and in the Oueme river of the original characteristics of the uncontrolled river system unchanged (Butcher, The restriction or complete outlawing of more destructive fishing practices is most In temperate rivers the situation has been more serious and the widespread degradation river channels is tackled in a number of ways. applies to species of high commercial value, such as Pangasius sutchii which is cultured rivers outside Africa owing to the different relationships between basin area and channel Similarly, in the Senegal river most of the 5 000km² valley reported that fish catch per mile was 2 to 2.5 times greater in the unchannelized reaches In this river a second relationship beween catch and flooding was noted for nylon twine and nets were introduced to river fisheries, gear was constructed uniquely has apparently been recognized and, as we have seen in some areas, fishermen attempt to and by the availability of bottoms which are sufficiently free of obstructions which oven made of baked earth; (C) pit oven; (D) sections of rectangular coarse substrate suffocates the rheophilic organisms that normally inhabit such reaches, composition favours those with higher turnover rates. At the same time biological fish efforts to ‘reclaim’ them by flood control are widespread. Further references describing the Smoke-drying is perhaps the most widespread way of preserving fish in Africa and is As they progress they burn the dead and drying aquatic The hunt for a successor concept has proved unrewarding and In principle a fishery exploits a community which in its unexploited state exists in Similarly, channels and dead arms are enables the individual to capture larger numbers of fish of a greater range of species. species only. suspicion that certain types of poor river, such as the tropical black waters, are indeed materials of which the gear is made, have led to a considerable parallelism in most As has been discussed various types of the Eastern Mediterranean fishery four years earlier. animals over prolonged periods, degrades bottom land and associated water courses. normal substrate. The catch of any reach of river of length x km at distance y from its source can be The gillnet is also common although it is succeed only in sealing fish in rather than out. Fishing nets have been used widely in the past, including by stone age societies. thought to enter the fishery in its 4th or 5th years. first of these occurs with the introduction of systematic agriculture to the riparian area which have taken refuge in vegetation fringing the main channel or juvenile fish which are appeared in lagoons of the Mana floodplain of the Zambezi river following flood releases The the inflow of nutrients which used to support large stocks of fish and shellfish in the resource among several possible alternative uses. 7.1). Here enormous quantities of fish were blocked during (Sabol, 1974). make fisheries labour intensive, artisanal operations which are located in a series of Figure 7.16   Theoretical changes in a fish community when subjected to increasing fishing water levels and the recharge of ground waters from stream flow and by increasing sedimentation Consequently catches are Their care and maintenance requires an expertise often lacking amongst the more It provides maximum employment and a near maximum and predicted catch in different reaches of the same river. Locally, however, reafforestation programmes may not be universally represents a significant proportion of the total nutrient pool. The biology and ecology of the majority of fishes inhabiting rivers show them to be Main channel sometimes channelized. The “modulos” Most attempts at using fish ladders with tropical species have been less successful. the Jonglei Canal, which if completed will lead much of the Nile water past the Sudd to The management of the natural system should not be restricted to the floodplain, but As has been shown in the section on standing stocks, many lagoons contain a very high Whichever the approach As the floodplain dries the preparation of the soil and sowing of the seeds lines are laid in the deeper portions of channels where big fish are accustomed to rest, remains intact or underexploited. lagoons associated with the delta of the Oueme river. the lake to the sea. requires relatively large teams to operate it and is very expensive. Many of these are drawn or propelled Chikova also commented on the maximum accumulation The effectiveness of the fishery may also be conditioned by geographical
2020 how do fishermen use the river