T. Petr, Senior Fishery Resources Officer
Fisheries Department, FAO, 00100 Rome, Italy
The expected one billion increase in population over the next 10 years will require more food, much of which is to come from the expansion of irrigated land. As a result the demand on water resources will be even greater than at present. New engineering works will be required, many of them in arid and semi-arid zones. Thus, the natural water systems will be further modified through more dams, reservoirs, channelization and water diversion, and the water quality will further deteriorate as some water bodies will receive agrochemicals and excess of nutrients from irrigated fields. All these changes need to be taken into consideration by fishery scientists, planners, managers and decision makers. In Central Asia and southern Kazakhstan over 95% of the total water use is for irrigated agriculture. Under such conditions, fishery management is a challenge as it requires that managers adjust to conditions created by the manipulated environment. In spite of the considerable experience gathered in Central Asia with introductions of exotic species and their food organisms, in the long run this has only succeeded in arresting the decline in fish catches but has not led to a sustainable growth in fish stocks. With the increasing population the demand for fish is growing and this requires the introduction of a more dynamic approach to fish production which would enable it to keep pace with or surpass the growth in human population. Wide exchange of information between the countries of Central Asia and other countries of the arid belt in Asia through an expert consultations or another similar mechanisms would be a good start for developing better strategies for fisheries development in irrigated areas.
Water abstraction for irrigated agriculture is a common practice worldwide. It has been estimated that about 36% of total crop production comes from the 17% of arable land that is irrigated. The recent FAO study "Agriculture towards 2010" estimates that in the year 2010, 45% of the global food production will come from irrigation.
In developing countries 80% of water used is for irrigation. To develop irrigation on such a large scale, many engineering works are needed. At present there are over 36 000 dams in the world (Pircher, 1993), with an equal number of artificial water storages, many of which serve irrigation. Some rivers now have a cascade of reservoirs, with little or no free flowing water in between them. The impact of damming the rivers on fish stocks is well known: the riverine fish stocks in dammed rivers become greatly diminished and in the best circumstances are replaced by fish species of standing waters. As damming for irrigation serves to store water for its diversion into irrigation canals, additional negative impacts on fish follow: pumping and water distribution are the most damaging for the fish, with especially the young fish mortalities approaching 100% in some cases, where irrigation uptake and diversion coincide with the peak periods of fish reproduction and nursing.
In arid and semi-arid zones water of some rivers is completely diverted and used for irrigation. Such rivers may cease to reach their original destination, i.e. the sea or a terminal lake. But the most common effect of withdrawals of water for consumptive use is the reduction of the flow downstream of abstraction. When coupled to reservoir storage, the pattern of flow can be significantly altered. Capture fishery activities depend on maintaining a connection between the floodplain and the river channel. Loss of the floodplain and of channel diversity create serious environmental consequences.
In 1987, in 93 developing countries of the world, a total of 164.7 million ha of land was irrigated. This is expected to increase to 220 million ha by year 2000 (Rydzewski, pers.comm.; World Agriculture Toward 2000, FAO 1993). The UNDP is looking for a 3% compound rate of growth in irrigated agriculture to meet the needs of an extra one billion people in the next 10 years (Pircher, 1993). The importance of irrigation is highlighted by its relation to arable land: Asia - 33%, Near East and North Africa - 21%, Latin America -8.5%, and Africa 2.7%. Within each region there are great variations, with for instance Egypt 100% and Pakistan 78% dependent on irrigation.
The quality of water available to agriculture is as important as the quantity. Depending on the sensitivity of the crop, when the composition of dissolved salts and pollutants in the water exceeds threshold levels, crop production decreases with increasing concentrations. The same applies to freshwater fish. Salinization of surface waters resulting from reintroduction of drainage and wash water from irrigated fields is a common problem in arid and semi-arid zones. While water with salinity over 1 mg/l is considered unsuitable for the usual crops, less is known about water salinity levels harmful to especially the young of the native fish of arid and semi-arid climates. Agricultural practices can also affect surface and ground water quality. Excess plant nutrients in surface runoff and deep percolation from both irrigated and rainfed areas can contribute to eutrophication of surface water bodies and to the growth of aquatic weeds in canals and water courses. Effluents from agro-industries and aquaculture also contribute to serious water quality problems. A heavy use of pesticides and defoliants, such as required for cotton production, is a major hazard for fish and the end consumers - birds and man. Where drainage and wash waters are diverted into desert depressions without an outflow, concentrations of agrochemicals there may gradually increase to unacceptable levels making the fish unsuitable for human consumption. An example is the Sarykamysh Lake in Karakalpakstan in Central Asia (Pavlovskaya, this volume).
However, irrigation can also assist in developing new types of fishery. This is a major challenge for fisheries management and if the already available management know-how is applied conscientiously, much can be achieved. Manipulation of rivers for irrigation results in the creation of reservoirs and irrigation canals. Often new lakes form from seepage water alongside the major canals, and seepage and drainage discharge may also create large areas of wetlands. Eventually, where drainage waters are discharged into depressions, new water bodies may form, some of which can reach sizeable proportions. Each of these water bodies can be managed for fisheries purposes, unless the water is of very poor quality. While our experience with managing water bodies resulting from engineering works required for large-scale irrigation is much better for fisheries in high rainfall humid tropical zones than for the arid and semi-arid zones, considerable experience also exists in the CIS (Confederation of Independent States) countries, which were among the first to transfer or introduce a number of fish species from distant water catchments, mostly within the ex-USSR, to arrest the decline in fish stocks in rivers and reservoirs through establishing new fisheries on introduced species. Not only fish were introduced, but also their food organisms, such as mysids, gammarids, cladocerans and molluscs. A long-term monitoring of the impact of fish transfers and introductions into reservoirs is also available and makes possible the evaluation of the impact of this management measure. Similar experience is also available for artificial terminal lakes, such as Sarykamysh, where in addition to following the impact of the gradually increasing salinities on fish, concentrations of selected toxicants in fish and water have also been monitored.
Another well tested management approach is the use of fish to control aquatic plants in irrigation and drainage canals. This has been tested in a number of countries, including USA (Florida) and Egypt. The grass carp effectively controlled especially the submersed plants and the cost of stocking the fish can be turned into profit where the fish is marketed (van Zon, 1982). The control of aquatic plants has been successfully applied in the Karakum Canal which branches off the Amu-Darya River in Central Asia.
A better use of drainage and seepage waters for fisheries is fully justified when considering the costs of soil rehabilitation for agriculture. Investment in land drainage today is in the order of US$ 1000-2000 per ha (Rydzewski, pers.comm.). A large quantity of water is needed to keep the soil salinity low; this must be added to the typical annual water use per hectare of 12 000 m3, with water salinity of 300 mg/l, which can potentially leave 3.6 tons of salt per hectare. Return of the salts into the river aggravates the living conditions for aquatic organisms but also can make further use of the river water for irrigation impossible. South Australia's stretch of the Murray River now has salinities over 1000 ppm which is twice the level set by the WHO as acceptable for drinking. Some fish, such as tilapias, can make good use of salinized waters. The efficient uses of the brackishwater environment, including artificially salinized waters resulting from agricultural practices, for fish production becomes a vital alternative. For example, three species of the tropical tilapias (Oreochromis mossambicus, O. niloticus, O. aureus) as well as the hybrid red tilapia grow well at salinities of 10 ppt (Suresh and Kwei Lin, 1992). But some freshwater species of temperate waters such as the common carp and pikeperch are also quite tolerant of saline waters, and they have proved very successful in slightly saline waters of Central Asia.
The damming of the rivers in Central Asia and creation of reservoirs had a major negative impact on the local fish fauna that required floodplains for their biological cycle. Dams have also blocked the migratory path of fish of the Amu-Darya and Syr-Darya, with several species, viz. shovelnose, sturgeon and Aral trout now threatened with extinction (Pavlovskaya, this document; Kamilov and Urchinov, this document). A further problem has been caused by the gradual desiccation of the Aral Sea which functions as the final destination for migrations of some fish species, and from which other species initiate their upstream migrations. Thus, as a result of the large scale consumptive irrigation uptake, the original fish fauna of Central Asia has been greatly disturbed.
In CIS countries this situation is not limited to Central Asia. Similar problems have been faced in Kazakhstan, in Russia, Ukraine and Azerbaijan. In Kazakhstan, damming of the Ili River has contributed to fishery problems in Lake Balkhash, the final destination of the Ili. There the problem is largely associated with the gradual desiccation of the deltaic lakes in which many fish previously spawned and found excellent nursery areas (Petr and Mitrofanov, 1995). The same problem was faced in the deltas of the Syr Darya and Amu-Darya rivers. There lakes started desiccating as a result of the drop in the water level of the Aral Sea, which combined with the virtual stop in delivery of the river water to the lakes from upstream as all the river water was used for irrigation.
On the Don River, irreversible water uptake for irrigation plus evaporation from the water surface consumes 45% of the water. After the construction of the Tsimlyansk dam, the downstream discharge declined by 24 per cent. The worst affected were the spring discharges, i.e. during the period most important for fish. Engineering works on Kuban (Ukraine) serve exclusively for irrigated agriculture in Krasnodar and Stavropol regions, and as flood protection. The Kuban River now has 14 reservoirs, retaining 5.62 km3 of water. Three km3/y of water is used for irrigation in the Stavropol region. During the April-August period sturgeon enter the river for breeding, and there is also a passive downstream drift of the young fish. The river discharges have declined from a mean of 5.9 km3/y to 3.6 km3/y, and water discharge into the delta lakes declined from 5.3 km3 to 1.3 km3/y. This has led to a reduction in spawning sites in these lakes from 169 000 ha to 86 000 ha, to a reduced water depth, increase in salinity, eutrophication and as a consequence to reduction in the stocks of migratory fish (Dubinina, 1992).
The irreversible water uptake from the Ural, Terek, Kura and several other rivers of the Caspian Sea basin now reaches about 10% of the long-term mean, with 20% reduction in discharges during the spring season, the most important for the fish life cycle. Lower discharges also result in higher levels of water pollution.
Defoliants, pesticides and fertilizers used in irrigated areas and around them eventually end in rivers, reservoirs and drainage lakes. The situation is known to be critical especially on the Lower Amu-Darya, but also much further upstream. The use of defoliants in orchards and on cotton plantations of the middle Zarafshan leads to their high concentrations in soils, from which the agrochemicals are washed away into rivers or are carried away in dust storms. Both the residents of Bukhara who take water from the Kuyumazar reservoir, and populations on the Lower Amu-Darya have been exposed to high doses of agrochemicals for over 40 years (Rakhmatullaev, 1993). No doubt the same agrochemicals are concentrated in the reservoir fish. The worst concentrations appear in the fish in terminal water bodies, which are maintained by drainage and wash waters from irrigated fields. Such fish are unsuitable for human consumption. Discharge of drainage waters from rice fields has had a negative impact on all aquatic organisms in the receiving water body, especially on the invertebrate fauna on which the fish feed. Kholina and Vasileva (1992) calculated the economic loss from the loss of fish and concluded that on the lower delta of the Volga River fish production should receive priority, and the area of the rice production should be reduced. The use of toxic chemicals should be banned.
Fishery managers in Central Asia and arid Kazakhstan have been dealing with the continuously changing conditions as best as they can. The major tool applied has been the introduction of fish and fish food organisms from outside Central Asia and arid Kazakhstan, both from Asia and Europe. Far Eastern cyprinids (Chinese carps) with pelagic eggs and larvae have proved to be very adaptive, especially to conditions in clear waters of major irrigation canals and reservoirs, and have established self-reproducing stocks. A number of introductions were carried out prior to the major impact of the regulatory measures serving primarily irrigated agriculture and hydropower production. The purpose of such introductions into the large natural terminal (and saline) lakes, i.e. Lake Balkhash and Lake Issyk-kul, has been primarily the increase in fish production. The impact of these introductions has been closely monitored, and analysis of the data often led to more introductions. At present, there is probably not a single water body in the region left with only the original indigenous fish fauna (Petr and Mitrofanov, 1995). Where there are fisheries, the proportion of introduced fish species may constitute 50% of the catch (Lake Balkhash) or even more.
Fishery managers in the region have concentrated on fish production from four major types of water bodies: (i) natural terminal lakes, such as Balkhash and Issyk-kul; (ii) water storage reservoirs; (iii) major irrigation canals, reservoirs and lakes fed from them, and (iv) newly established terminal lakes, such as Lake Sarykamysh and the Arnasai system of lakes, fed by drainage and wash water from irrigated fields.
While the Aral Sea has completely lost its fishery significance, Lake Balkhash has been effectively managed through introduction of a number of fish species and their food organisms (Petr, 1992). The introductions, staggered over many years, have resulted in peaks and lows in fish catches, with a maximum of 18 650 t in 1941, which was far above the unmanaged fish production based on only native fish stocks. In 1963, 83.5% of the total catch was represented by common carp, Leuciscus and pikeperch - all introduced. However, the pikeperch later proved to have almost eliminated the native snowtrout Schizothorax argentatus and Perca schrenki. In Lake Issyk-kul in Kyrgyzstan, by the 1970s an intensive fishery had drastically reduced the stocks of native fish; these were further affected by introducing two predators, pikeperch and the Sevan trout (Salmo ischchan issykogegarkuni). The present fishery exploits two native fish species plus two introduced piscivores, i.e. pikeperch and the Sevan trout. The lake level is currently declining by 5 cm/year (Savvaitova and Petr, 1992) and this lowering reflects diversions for irrigation, although this is not the major cause of it. However, it is recognized that any future expansion of irrigated agriculture must be achieved without increasing diversions from inflowing streams and rivers. One way to achieve this is to change irrigation practices. At present, about 90% of irrigated land involves furrow irrigation in which part of the water evaporates and the rest drains into the lake but contains fertilizers and harmful agrochemicals.
In 1988 in Central Asia there were over 40 reservoirs either already existing or under construction, with a total water storage of approximately 50 km3 (Nikolaenko, 1988). Their major purpose is the storage of sufficient water volume of required quality for irrigation use. Fishery requirements have been subordinated to other requirements, but the situation has been changing recently. The urgency for a new policy is evident as waters are polluted by agrochemicals and industrial pollutants, which act as stressors on fish. Considerable damage to juvenile fish stocks is caused by pumping water for irrigation and other purposes. According to Pavlovskaya (this document) about 90% of the young enter the final irrigation canals and perish on irrigated fields. Virtually none of the Amu-Darya pumping stations and canal heads have fish protecting devices.
In Uzbekistan a fishery exists on seven reservoirs out of the total of over 20. Reservoir management has focused on the following: introduction of new fish species and fish food organisms, management of spawning sites, fish protection, improvement of the efficiency of fishing methods, intensification of fish production in separated or isolated parts of reservoirs, fish production in the littoral zone, and introducing pen and cage culture (Kamilov and Urchinov, this document). Those reservoirs with a low primary and secondary production also have poor fish production. However, where Chinese carps which feed on macrophytes or phytoplankton were introduced, there has been an increase in fish production. It is generally recognized that establishment of reservoirs has had a positive impact on the growth rate of the wild form of common carp, but its recruitment is hampered by sudden drops in water level, exposing its eggs to desiccation. Such water releases are requested by agriculturists for irrigation during the spring season. A fishery management programme has been prepared for each major system of water bodies in Uzbekistan, and it should result in substantial increases in fish production both for the commercial and recreational fishermen (Kamilov and Urchinov, this document).
Fishery statistics for Uzbekistan show that fishery managers have been able to balance losses caused to fisheries through management measures. However, maintaining sustainable growth has not yet been achieved. Considerable potential for increasing fish production exists in freshwater reservoirs and several lakes, with annual yields estimated to be at present less than 10 kg/ha in Uzbekistan and 12 kg/ha in Kapchagay reservoir in Kazakhstan (Petr and Mitrofanov, 1995). A management programme has already been prepared for each Uzbekistan reservoir and this should make it possible to increase fish yields 4 to 6 fold (Kamilov, this document).
In Uzbekistan there currently exists a net of irrigation canals of perhaps 13 000 km as well as 12 700 km of drainage canals. Some of the canals now interconnect several river systems which, until recently, were isolated. Today, as a result of irrigation needs, the Syr-Darya is connected through irrigation canals with the Sanzar River, and the Sanzar with the Zarafshan. The Zarafshan is connected through the Eski-Angar canal with the Kashka-Darya River, and the Kashka-Darya through the Karshin main canal with the Amu-Darya. The Zarafshan River is connected with the Amu-Darya through Amu-Bukhara and Amu-Karakul canals. Connecting various rivers by canals has played an important role in the current fish fauna set-up of the individual water bodies (Kamilov and Urchinov, this document). The fish are now able to move freely from one river basin to another, and this, combined with introductions from elsewhere, especially from the Far East, has led to the enrichment of species diversity in Central Asian water bodies. The construction of inter-connecting canals, such as Amu-Darya-Bukhara, has also improved the fish production by stabilizing water levels in some lakes, previously subjected to drying out which periodically killed eggs and fry, especially those associated with aquatic plants (Urchinov, this document).
Aquatic macrophytes represent a major problem for irrigation canals, and the introduction of grass carp and silver carp has assisted in clearing these aquatic weeds. It took only a few years for aquatic plants to be subdued in the Karakum Canal, after the grass carp was introduced there in 1960. The combination of three Chinese carps - grass, silver and bighead - has been considered very suitable also for maintaining good water quality. Three carp species constituted 75 to 80 per cent of the total catch from the canal and its associated water bodies (Charyev, 1984).
Freshwater lakes situated in deltas of the Amu-Darya and the Ili have been endangered by the diminished inflow of freshwater from upstream and by regulated flow rates, which either completely eliminate the annual cycle in water discharges, or change them so that they do not coincide with the demands of fish for reproduction and nursing. A further problem has caused by the drop in water level of the Aral Sea which has caused the drying out of many delta lakes of the Amu-Darya and Syr-Darya.
Fisheries management of terminal lakes established from drainage waters face the most difficult decisions as the water quality is gradually deteriorating. While initially, during the first phase of their formation, these lakes represent a conducive environment for rapid fish colonization and high fish production, before long their environment starts deteriorating through salinity increase and agrochemical inputs (Pavlovskaya, this document). This leads to decline in both fish production and fish species diversity, replacement of commercially valuable fish species by smaller sized fish, and to accumulation of toxic substances in fish flesh to a level which prevents their consumption. There is no doubt that the future of such lakes will depend on the future strategies of the Government (Petr and Mitrofanov, 1995). However, for the foreseeable future the water quality in terminal lakes established from drainage waters can be expected to further deteriorate. In such cases, fishery management efforts should be directed towards freshwater reservoirs, lakes and major irrigation canals which offer considerable opportunities for increasing fish yields.
Present Government strategies in the region focus on the rehabilitation of rivers and terminal lakes with the aim of arresting and reversing the process of salinization of waters and of maintaining water level in lakes. Such an approach is welcomed by fishery managers as it allows them to develop strategies for optimizing fish yields under more stable conditions. The freshwater lakes, reservoirs and wetlands formed from seepages near irrigation canals have considerable potential for raising fish yields. Culture-enhanced techniques are still another approach which is largely waiting to be applied in the region. Through the judicious application of the available fishery management methods, the current freshwater fish yields in the region could easily increase by ten-fold within the not too distant future.
The sole responsibility for successful fisheries management does not rest entirely with fishery specialists, including fishery planners. What is needed is to place Government priorities for food and other crops and animal husbandry, as well as for hydropower production, into the framework of a holistic approach, leading to implementation of an integrated management programme in which fisheries will be elevated from its frequently subordinate position to an equal partner in discussions and the decision making process (Petr and Mitrofanov, 1995). A fundamental change in agricultural use of water may be needed, such as conversion from largely extensive agriculture, demanding high volume of water to well-managed intensive agriculture based on low demand for water, if all sectors are to equally share in the rational and environmentally friendly use of the water resource.
With few exceptions, such as the Nile in Egypt and Sudan, inland waters of arid and semi-arid zones have been largely neglected by fishery scientists of the world. This neglect could be understood as these zones are usually sparsely inhabited and often the local inhabitants are not fish eaters. Interest in the inland water bodies has increased with their increasing number and diversification as a result of large-scale development of irrigated agriculture. New dams stored water for later use, reservoirs formed and extensive systems of irrigation canals were constructed. Additional water bodies appeared as a result of discharge of drainage waters. Interconnecting river basins through canals has led to the invasion of new species to catchments which formerly did not have them. In a number of countries fishery scientists have initiated transfer of fish to enhance fish production in water bodies which appeared to have only few commercial fish species, or where fish stocks have already been depleted. Fishery management of water bodies in arid regions has emerged as a specialized field which has to consider how to deal with the unstable aquatic environments which are manipulated largely for irrigation water demands.
In Asia, the arid and semi-arid zone extends from the Mediterranean to China, and includes dozens of countries. In most of these irrigated agriculture is an important integral part of the economy and a sector on which the food production almost entirely depends. Irrigated agriculture is the government's priority, which dominates government decisions on allocation of water resources. The role of fisheries managers is therefore subordinated to this government policy. Fisheries management needs to adapt to this situation, and in a number of countries this is being done quite successfully.
In Central Asia and Kazakhstan, experience with the managing of freshwater fish stocks has been gained both empirically and on the basis of scientific approaches. The empirical knowledge was gathered through a series of adjustments to changes in fish stocks, which were exposed to three major impacts: overfishing of the most valuable fish species, manipulation through introductions of exotic species to boost the fish production, and physical modifications of environment by irrigation structures. As in other natural water bodies, the successes were mostly temporary, with often spectacular increases in fish stocks after a new species introduction, which then was followed by a sharp decline, to be followed by another introduction, as for example in the Balkhash Lake. This has been accompanied by scientific studies trying to find out why one or another fish species was doing so well and others not. Provision of fish food organisms has always been high on the minds of scientists, and this has led to transfers of mysids, gammarids, cladocerans and molluscs in some water bodies.
The creation of engineering works for irrigation has challenged the fishery scientists and fishery managers to identify the best ways to produce and harvest fish from the diversity of water bodies, but also raised the question of how to protect the fish from high concentrations of agrochemicals washed out from irrigated fields. This is the current situation, as best shown by examples from Uzbekistan and Karakalpakstan (see the other documents in this publication). Fishery yields have been largely kept at the same level, which is not considered satisfactory, as the population in the region has been rapidly increasing. Traditionally, most people in the region prefer red meat to fish, therefore any increase in the demand for fish could be satisfied through import of relatively cheap fishery products from elsewhere in the CIS. However, with the formation of independent countries after the USSR ceased to exist, the cost of imports is becoming too high which limits the amount of fish the local population can afford to buy. It is therefore the right time to place more effort in rational development of inland fisheries. Uzbekistan now has a fisheries development plan for each water body which, if implemented, should result in substantial increases in fish production. The Government realizes that the diversity of water bodies resulting from irrigated agriculture needs to be better utilized for fish production, and fishery development is now being placed among the government priorities. Due to long isolation of these countries from the outside world, with the exception of the other ex-USSR countries, there is a need for assistance in planning and implementation of projects which would employ modern fish stock enhancement technologies.
Wide exchange of information among the countries of the arid and semi-arid zone could be a start for developing better strategies for fisheries development in irrigated areas. An international meeting, if held, could have the following agenda: review of the current extent of fishery management in the countries of the region; impacts of engineering works created for irrigation, on fish stocks and fisheries; existing fishery management strategies applied to counteract the negative impacts of irrigational uptake, diversions and salinization of water bodies; institutional arrangements and intersectoral collaborative mechanisms for optimizing the land and water resources in the context of multiple-use in arid environments; identification of problem areas for international collaboration and development of mechanisms for international collaboration in the region. Such a meeting should be a priority for the governments in arid and semi-arid zones, where irrigated agriculture is the mainstay of food crop production.
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