SUMMARY
1. INTRODUCTION
2. IMPACT ON FLOOD CONTROL DRAINAGE AND IRRIGATION PROJECTS ON FISHERIES
3. MITIGATION OF ADVERSE IMPACTS OF FCDI PROJECTS
4. OPTIONS FOR INTEGRATION OF FISHERIES DEVELOPMENT COMPONENTS IN ALREADY COMPLETED FCDI PROJECTS
5. CONCLUSIONS
REFERENCES
by
Ainun Nishat
Professor, Dept. of Water Resource Engineering, Bangladesh University
of Engineering & Technology, Dhaka-1000, Bangladesh
and
Muhammed Ali Bhuiyan
Associate Professor, Dept. of Water Resource Engineering, Bangladesh University
of Engineering & Technology, Dhaka-1000, Bangladesh
The present trend of land and water development, with the single objective of increasing agricultural production, mainly paddy, has led to neglect to other water sectors, such as fisheries, navigation, environment management and industrial water supply. The main casualty of the present development process has been the fisheries sector. It is now recognized that great opportunities exist for utilization of the land and water resources of the country in an integrated, balanced and comprehensive manner that will not only lead to growth both in the agriculture and fisheries sectors but also resolve many environmental problems.
In the past, the water development included interventions aimed at i) flood protection with polders in order to enhance agricultural productivity, ii) drain wetlands for making them available for crop production, and iii) provide irrigation by pumping either groundwater or surface water. These have led to loss of habitat and prevented the movement and migration of fish from rivers and waterbodies to flood plains and vice versa. This has contributed to a rapid decline in openwater fisheries. However, flood protection improved conditions for expanding and intensifying pond fish culture.
To mitigate the adverse affects of flood embankment and regulators in flood control drainage and irrigation projects (FCDI) the introduction of fish passes has been proposed under the Flood Action Plan and, at present, pilot level projects are being implemented.
While mitigatory measures are being evolved, there exist many opportunities for integration of fisheries development components in already completed FCDI projects. These include i) fish stocking and fish cultivation in burrow-pits; ii) aquaculture in ponds/tanks; iv) aquaculture in dead channel/rivers; v) integrated fish farming; vi) fish culture in paddy fields; vii) pen culture of fish; and viii) shrimp culture in the coastal polders.
Finally, the paper recommends proper integration of fisheries management requirements in all future water development projects.
There is a distinct pattern in the annual water cycle which dominates life in Bangladesh: excessive water during the monsoon, causing flood, and insufficient water during the dry season, creating a drought-like situation. These two extremes have influenced the planning strategy for the development of land and water in Bangladesh requiring effective measures for flood mitigation, irrigation and drainage. Water resources development, including flood management, has till now been considered the key factor in the economic development of Bangladesh. In fact, developments in irrigation together with flood mitigation and drainage infrastructure, in areas where they have already been completed, have created a regime wherein other agricultural inputs may be effectively utilized to enhance the yield rate of rice crops. However, this trend in land and water development with the single objective of increasing production in agriculture (mainly paddy), has led to neglect to other water sectors such as fisheries, navigation, salinity control in the coastal area and domestic and industrial water supply. Concerns are being expressed about the various adverse aspects of water development projects and questions are being raised about the present strategy of land and water management in the country. It is being recognized that great opportunities exists for utilization of the land and water resources of the country in an integrated, balanced and comprehensive manner that will not only lead to growth, specially in the agricultural and fisheries sectors, but also resolve many environmental problems (Nishat 1986, UNDP 1989, and MPO 1986, The World Bank 1989). The main casualty in the present development process has been the fisheries sector.
A predominantly agrarian society dependent on climate and weather, evolved in Bangladesh over the years. Excepting for the farmers themselves lifting water from ponds and streams to provide supplementary irrigation by indigenous methods, there were no major efforts in water development. Agriculture was mainly rain-fed and the traditional rice varieties, aus and aman, were the main crops. There was no conflict with growth of fish in the wetlands, food plain and rivers.
But with the rapid increase in population, it soon became a fact of life that Bangladesh suffered from a chronic shortage of foodgrain. It became clear that increased production of foodgrain had to come from intensified use of available land as well as by increasing the yield from the crops grown, as there was virtually no additional land to be brought under cultivation. The situation was reviewed in 1957 by a UNDP-sponsored mission and it was concluded that water development was essential for higher agricultural production and that the control of floods was the central issue (Siddiqui & Nishat 1986).
In 1959, the present Bangladesh Water Development Board (BWDB) was established and was assigned responsibility for water development, i.e. to plan, design, construct, operate and maintain such development schemes. A Master Plan was prepared in 1964, the broad strategy of which was to reduce damage to crops, first, by providing flood protection, and then, boosting crop production through use of modern agricultural techniques, e.g. chemical fertilizers. Irrigation was to be introduced at a later stage. Such a strategy essentially required large flood-protection schemes and most of the major projects of BWDB have been developed by following this strategy. In the meanwhile, the present Bangladesh Agriculture Development Corporation (BADC) had been created in 1961 and entrusted with the task of procurement and distribution of inputs and equipment for modem agriculture, such as tractors, low lift pumps (LLPs), tubewells (TWs), seeds, fertilizers and pesticides; and they became the instrument for implementation of small, quick maturing irrigation projects, i.e. installation of LLPs and TWs.
In 1972, the Land and Water development strategy was reformulated with assistance from IBRD and high priority was attached to small schemes that emphasized the use of agricultural inputs, winter irrigation and quick drainage of low-lying areas for cultivation of winter boro paddy. This strategy constituted a major ingredient in the programme of the BWDB and BADC, and was reflected in all the Five-Year Plans of the country formulated so far. These activities succeeded in giving a boost to foodgrain production.
To respond to the need for development of an integrated land and water development strategy, the National Water Plan (NWP) project was initiated in 1983. The project was given the task to formulate a perspective water development plan for the period 1985-2005 based on a comprehensive assessment of all natural, human and financial resources. The plan was to allocate a fair share of the scarce water resources to various sectors and to formulate water development strategy and plans so as to ensure harmonious growth in different water use sectors. Phase-1 of the NWP study was completed in 1986. In Phase-11, completed in 1991, the Phase-1 report was updated. Unfortunately, agricultural production remained the target of the NWP and the incorporation of the requirements of the fisheries sector continued to remain unattended.
In 1987 and 1988, Bangladesh experienced two of the most severe floods on record. Widespread damage was caused to crops, roads railroads, cities and towns, and more than 3000 people lost their lives (World Bank 1989). Floods cause a major setback to the country's economy, in part because of the heavy expenditures incurred by the Government in its relief efforts and in part by the disruption of economic activities. The flood of 1988 stimulated the Government to undertake a comprehensive review of the planning approach of ongoing activities and work began on a flood policy study and a flood preparedness study (UNDP 1989). Studies were also carried out by professionals from Japan, France, U.S.A and China (Nishat 1992). All these studies were reviewed and an integrated approach for flood mitigation based on the concept of 'controlled flooding' was recommended (UNDP 1989). The Flood Action Plan (FAP) was formulated and study of different components under FAP is going on (World Bank 1989). In fact, it was envisaged that the studies to be undertaken under the FAP umbrella would pay full attention to the needs of the fisheries sector while preparing land and water development plans. But though some attention to the fisheries sector has been given in the FAP's regional studies, the focus still remains concentrated on the agriculture sector. However, one special study was commissioned, known as FAP-17, which was to recommend how fisheries development could be integrated in land and water development projects. The FAP process is expected to be reviewed by the end of 1995, in order to set out the future course of action. As such this National Seminar is being held at a very opportune moment and its recommendations would provide concepts and strategies for integrating the fisheries sector in the management of the country's land and water resources.
2.1 Impact on the capture fisheries
2.2 Impacts on culture fisheries
Impacts on fisheries due to the present Flood Control, Drainage and Irrigation (FCDI) projects have been evaluated in a number for studies (e.g., Ahmed 1987). The FAP has contributed significantly to the literature. Notable among them are the Fisheries Study (FAP-17), the FCDI Agricultural Study (FAP-12) and the Northeast Regional Study (FAP-6). Growing awareness of the cumulative negative impact on inland capture fisheries of the progression of flood control embankment and polder type projects throughout Bangladesh, and of the general lack of basic information with which to assess the scale of the problem, led to the inclusion of a fisheries component in the terms of reference for FAP-12, wherein 17 projects were evaluated through the Rapid Rural Appraisal (RRA) technique. Five of these projects underwent further in-depth study through Project Impact Evaluation (PIE) methodology (FPCO 1992a). This section summarises the findings of FAP-12 on the impacts the FCDI projects have had on fisheries.
The RRA surveys were carried out from late April until mid-July 1991, during the first half of the monsoon flood season when fish production is lowest, whilst the PIE'S took place in the second half of the monsoon, from July to October. The latter period includes the peak time for subsistence floodplain fishing and the time when the beel and river fisheries are revived and move towards their peaks around November to January. The timing of these studies was dictated by circumstances rather than by choice, but from the fisheries side, it was advantageous to see conditions during the flood season, despite the difficulty of contacting fish pond owners and fishermen.
The overall conclusion of FAP-12 was that there were two main areas of fisheries impact: firstly, relating to pond fish culture, which benefited from FCD, and secondly, inland capture fishing, which almost invariably suffered severe damage. The pond culture benefits accrued mainly to land owners and farmers, whose land-holdings already benefited from positive agricultural impacts, whereas the impact on capture fishing adversely affected large numbers of landless fishermen. The net impact was negative in the majority of cases.
Indications from the RRA surveys were that virtually all the projects contributed to the decline in fish stocks targeted by inland capture fisheries by obstructing fish mitigation routes, thereby reducing the riverine spawning stocks and preventing the return distribution of fish fry to the floodplain. Land reclamation by drainage works has greatly reduced the areas of permanent water bodies and, especially within FCDI projects, many once perennial beels have been rendered seasonal if not permanently dry. The spawning and rearing areas for a number of non-migratory, resident floodplain and beel fish species have, thereby, also been reduced, with similar effects on the stocks of such fish. Catch rates have also declined, with fishermen in several of the projects, studied claiming reduction of upto to 75 percent which they blamed in large part on the FCD project concerned. RRA findings with regard to submersible embankments, which only protect against early monsoon flood, were that they cause less damage to fish stocks because they only delay fish migrations to and from the rivers rather than prevent them.
Other significant findings pertaining to the capture fisheries were:
- All the projects, except for the submersible embankments have greatly reduced the right of free common access to catch fish for subsistence needs during the flood season.- Virtually all the projects, except for the submersible embankments have resulted in many former full-time fishermen having to seek other work, at least on a part-time basis. At the same time, there has been an influx of other landless people into part-time fishing for the first time.
- All the projects, except for the submersible embankments facilitate the development of enhanced commercial fishing, based on regular restocking of water bodies with hatchery-produced fingerling. Fishermen and traders confirm that this is happening, but they have doubts whether the stranglehold of the local elite and wealthy on such fisheries can be broken in favour of the fishermen.
- The existing designs for FCD sluices and regulators cannot be operated to enable fish to pass in either direction, and conventional fish ladders are not suited to the needs of local fish species.
An important PIE finding on capture fisheries was that the daily catch, per fisherman, now averages around 2.5 kg., compared with 4.6 kg before the FCDI projects. Current and pre-project control area averages are both lower than these, partly because fishermen on the affected areas have a better chance to make up some of their open water losses by catching pond fish for pond owners who lack the means to harvest their own fish. As expected, the great majority of fishermen reported decreases of 25 percent or more in catches of all the major species groups, namely the major carps, Hilsa, catfish, live fish (Shing, Magur and Koi) and the Snakeheads, showing that riverine and floodplain species were equally vulnerable.
RRA findings were that all the projects, except for the submersible embankments, created improved conditions for expanding and intensifying pond fish culture and culture-based fisheries in some other permanent waterbodies. However, it was also found that the anticipated benefits did not occur in parts of some of the projects which were subject to rainwater congestion caused by inadequate drainage provision or where there were frequent breaches of the embankments. Even in areas where flood protection could be maintained, the RRAs concluded that the response by pond owners frequently fell far short of expectation because there was repeatedly a general lack of credit to finance pond re-excavation and rehabilitation as well as problems stemming from multiple ownership of many ponds and the inability of aquaculture extension staff to meet the needs of prospective fish farmers.
Pond owners' views on the reasons for improved performance in the impacted areas included flood protection, higher fish prices, improved availability of good quality fish seed and improved technology, all leading to increased profitability., However, many problems still remain, notably the high risk of fish being affected by the current epidemic of ulcerative syndrome fish disease. The supply of fisherlings still presents difficulty in some parts of the country, and the risk of over-flooding is still unacceptably high.
The findings on the impact of FCDI projects on fisheries are summarized in Table 1. The principal conclusions arising from FAP 12 are:
- There has been a very substantial decline in the freshwater capture fisheries resources and catches concurrently with the implementation of major parts of the FCD and FCD/I programme.- Despite the general lack of reliable data, the study has established that fish stocks and production overall have fallen by more that 25 percent in recent years and that in some places the loss may be upto 75 percent as reported by many of the fishermen concerned. A major cause of the decline is the blockage of fish migration routes by FCD structures.
- Consequent on these declining catch rates, there has also been a drop of up to 50 percent in the number of full-time professional fishermen coupled with an influx of at least a similar number of new part-time fishermen according to RRA report. These changes are not recorded, but the pattern suggests that the total effort may not have greatly increased since the late 1980s.
- Given the reduction in fish stock size, even an unchanged level of fishing effort will cause overfishing and the present widespread use of illegal small mesh nets only makes matters worse. FCD and illegal overfishing are both implicated in the decline to date, but unless changed or checked both have the potential to inflict even greater damage in future.
- Among the recommendations for future mitigatory and remedial action, it is proposed that all future FCD projects give particular consideration to fisheries impacts, make appropriate adjustments to structural design and include specific mitigatory provisions to assist the fishing communities whose livelihood will unavoidably be adversely affected. The DOF must be fully involved and assisted where necessary. To marshal the resources needed, publicly-owned waterbodies in project areas should be protected and managed to optimize fish production instead of being drained. Riverine fish breeding stocks should be rebuilt by all possible means and, in particular, all existing fisheries regulations governing fish protection must be vigorously enforced.
Table 1: FCD/I Project Impacts on Fisheries (Source: FPCO 1993 a)
|
Project |
Type |
Capture Fishery Production |
Culture Fishery Production |
Fishermen's employment |
Fishermen's earnings |
Overall |
Remarks |
|||
|
Rivers |
Beels |
Flood plain |
Fish ponds |
Larger bodies |
||||||
|
Chalan Beel "D" |
P |
-2 |
-2 |
-2 |
+1 |
+1 |
-2 |
-2 |
-2 |
The loss 'leader' |
|
Kurigram South |
P |
-1 |
-2 |
-2 |
+2 |
+1 |
-2 |
-1 |
-2 |
Fish culture OK, otherwise negative |
|
Meghna Dhonagoda |
P |
-2 |
-2 |
-2 |
+2 |
+1 |
-2 |
-2 |
-2 |
Fish culture OK, otherwise negative |
|
Zilkar Haor |
S |
-1 |
-1 |
-1 |
0 |
+1 |
-1 |
-1 |
-1 |
Less damaging to fish stocks |
|
Kolabashukhali |
P(T) |
-2 |
-2 |
-2 |
+1 |
+1 |
-2 |
-2 |
-2 |
Good potential for fish culture |
|
Protappur |
P |
0 |
0- |
0 |
+1 |
|
0 |
0 |
+1 |
A neutral project |
|
Nagor River |
P |
-1 |
0 |
0 |
+1 |
|
0 |
0 |
-1 |
Without cuts would be -2 |
|
Sonamukhi |
D |
0 |
-1 |
0 |
+2 |
+1 |
-1 |
-1 |
0 |
Could improve |
|
Sakunia Beel |
P |
-2 |
-2 |
-1 |
+1 |
0 |
-2 |
-2 |
-2 |
Good potential for aquaculture |
|
Silimpur |
E |
-1 |
-2 |
-2 |
+1 |
|
-1 |
-1 |
-1 |
Sandy soil inhibits aquaculture |
|
Katakhali Khal |
E |
-2 |
-2 |
-2 |
+1 |
+1 |
-2 |
-2 |
-2 |
Area no longer a surplus fishery |
|
Halir Haor |
S |
-1 |
-1 |
-1 |
0 |
0 |
0 |
-1 |
-1 |
Less damaging to fish stocks |
|
Kahua-Muhuri |
P |
-2 |
-2 |
-1 |
+1 |
+1 |
-1 |
-2 |
-2 |
Could be improved |
|
Konapara |
E |
-2 |
-2 |
-2 |
+2 |
0 |
-1 |
-2 |
-2 |
Major restocking effort in beels needed |
|
Polder 17/2 |
P(T) |
-2 |
-2 |
-1 |
+1 |
-1(*) |
-2 |
-2 |
-2 |
Shrimp farming needs controlling |
|
BRE-Kamarajan |
E |
-1 |
-2 |
-2 |
-1 |
-1 |
-2 |
-2 |
-2 |
Drainage congestion floods ponds |
|
BRE-Kazipur |
E |
-1 |
-2 |
-1 |
-2 |
-1 |
-2 |
-2 |
-2 |
Erosion of BRE main problem |
Source: PLEs and RRAs
Project Type: P=Polder; P(T)=Tidal polder; S=Submersible embankments; E=Single Embankment, D=Drainage only.
Fisheries Impact: 0=No change; +1 = Increased by some extent; +2 = increased substantially; 1 = d
(*) The area of shrimp farms has reduced since Polder 17/2 were completed, so could be rated -2 but the remaining area seems stable, and with proper control could be expanded for benefit of local small farmers.
3.1 Life cycles of fish
3.2 Migration characteristics
3.3 Impacts of water control structures
3.4 Fish passes
3.5 Applications in Bangladesh
A major concern when embankments are used to protect areas from extreme floods in Bangladesh is the perceived detrimental effect on the important floodplain fisheries (FPCO 1992a, FPCO 1992b). There may be several reasons for this and one that has been put forward is that the gated structures (regulators) used to control the flow into the embanked areas, inhibit fish movement or damage fish in passage. It is possible to mitigate the negative impacts due to restriction of river bank overspill, through structural additions and/or modifications to flood schemes. Fish passes can be installed to assist both upstream migration and to facilitate downstream movement of adults and passive drift of hatchlings (FPCO 1992b).
Migrating adult fish, under normal flood levels, are most likely able to pass through existing structures, but the distribution of fish fry being carried downstream from the spawning grounds to the floodplains is limited and hatchlings are possibly damaged when passing through the regulators. The possible problems when fish fry negotiate regulators are:
- total obstruction to fish passage;- physical damage to the fish through contact with the structure.
- damage to the swim bladder through rapid changes in pressure; and
- damage arising from turbulence downstream of the structure.
A regulator of normal design using vertical life gates, will not completely exclude fish fry, but it may delay them if the gates are undershot and the gate opening is small. Damage to fish by contact with the structure would most commonly occur because the velocities are high. Culverts using impact energy dissipators are unsuitable for fish passage but this type of dissipator is used where tail-water depth is low and fish movement is not likely to be high. Culvert regulators could be improved to some extent for the passage of fish by increasing the size to minimize velocities and by streamlining the entry.
Damage to the swim bladders of fish could be a serious problem and is most likely to occur with undershot gates operating at small openings. Free surface flow, as occurs with overshot gates or fully open gates, will minimize this problem. Turbulence downstream of a regulator is not yet a proven cause of damage to fish fry in passage, but clearly it is preferable if the exposure of fish fry to the often violent downstream fluctuations can be minimized.
In order to evaluate the various options availabe to minimize the negative impacts of flood control infrastructure on fish production, it could be useful to discuss some basic issues with respect to the life cycle of fish and their migratory characteristics. This section has been based on FAP-17 (FPCO 1992b).
A great range of niches are available within the river floodplain complex which contribute towards the characteristics, great diversity and the high biomass of the fish present. Fish of tropical flood river systems tend to show rapid growth and short life cycles compared to lake fish or temperate species.
The life cycles and behavioral patterns of fish which inhabit river and floodplains that have well defined seasonal flood regimes are closely related to changing water levels and river discharge. Large annual fluctuations in volumes of river-and flood water cause seasonal shifts between predominantly aquatic and terrestrial environments. The fish and ecology are strongly influenced by the flood regime and the alteration between aquatic and terrestrial phases. Extreme oscillations, in conditions and in the distribution and availability of resources, exert a profound effort on the productivity, community dynamics, biology and behaviour of the fish. Life cycle patterns of behaviour that have evolved are synchronized with the cyclical nature of the flood regime that determines environmental capacity and food availability. The seasonal changes in the hydrology of the river and floodplain environment are probably the most important stimuli of changes in feeding and breeding activities, dispersal and movements of fish which,, in turn, determine, sexual activity, rates of growth, specific associations and oxygen requirements.
During the wet season, the over-bank spillage of floodwater from the main river channels through secondary rivers, onto the flood plain, provides important pathways for fish to enter and migrate into the floodplain area. The flooded floor plain presents a dramatic increase in environmental capacity (living space) and resources. As the floodwaters recede and the supply of resources upon the floodplain diminish, large numbers of fish retreat to the river channels and drainage systems (khals) and to the residual permanent waterbodies (beels). Growth is rapid in both juveniles and adults in the flood season, but slow or even negative during the dry season. Floodplains are the major food resource for the fish inhabiting tropical river systems.
The flood cycle is an essential element in the life history of most of the fish in the rivers. The inundation of the floodplain provides the spawning grounds, nursery areas and the major feeding opportunities for many of the 256 species which have been recorded as found in Bangladesh (Rahman 1989). Many of these species migrate considerable distances upstream, under the stimulus of the rising waters, to reach the spawning areas, and also move out over the floodplain as the waters spread. These fish depend upon the flood cycle to provide feeding grounds, space for reproduction and the environmental triggers that synchronize their life cycles with the flood cycle of the rivers. The movements of fish populations for spawning and feeding must be co-ordinated and it is the information derived from the changing water conditions during the flood cycle which provides the basis for such co-ordination.
Few flood river fish are confined to one habitat. The species that reside on the flood plain and beels at the height of the dry season tend to be those that have adapted to withstand limiting conditions (such as desiccation, isolation and deoxygenation) in the dry season pools. Of these, some are restricted to a small geographical area and make only short migrations (20-30 km). Others, however, migrate substantial distances, upto several thousand kilometres, between very different habitats.
For fish inhabiting seasonal floodplain river systems, the extreme spatial and temporal differences in the distribution of resources mean that the optimum habitat for feeding rarely coincides with that for breeding. The two sites may be isolated and separated and migrations between the two will have to be undertaken to optimize available resources. With breeding grounds upstream of the feeding grounds (floodplains), the relatively immobile eggs and hatchlings drift downstream towards the feeding grounds in the first stages of their development. The developing fish are then transported and dispersed by the floods through the secondary river systems and by the time they reach the floodplains they are at a stage in their development when they are able to exploit the rich food resources.
Fish migration is most commonly associated with a behavioral response to currents. The nature of this response can, however, change during the life cycle of the species, the fundamental distinction of response is between active upstream migrations, usually of adults to their spawning grounds, and the passive combined active/passive downstream migrations of juveniles. For the population to be maintained in the river, both phases need to be considered (Fig 2).
Figure 1. The seasonal cycle in a floodplain river (Source: FPCO 1992 b)
Figure 2. Basic pattern of migration between feeding, spawning and nursery habitats
Whilst this is the basic pattern, different species of fish differ in the extent of the various responses. With regard to migratory response, the fish communities of southern Asia are divided into 'black fish' which are essentially resident on the floodplain and 'white fish' which show some distinct migratory movement within the river system, usually associated with spawning.
The 'black fish' community are those which would normally retreat into beds or other residual water after the floods have receded. They are predominantly those species which are commonest in the kua or fish pits, which trap the last remnants of the floodplain waters. As the resident water is used ever more intensively, the dry season habitat and refuges for these species diminish.
The 'white fish' community can be divided into three categories, depending on the extent of migration:
- those with considerable longitudinal migrations, which may be followed by lateral migration onto the floodplain;- those with limited longitudinal migrating followed by latitudinal migrations onto the floodplain; and
- those which are truly anadromous, moving from the sea and into freshwater.
There are few direct observations on the migration of fish in the rivers of Bangladesh. It is necessary, therefore, to infer the most probable pattern of events from observations elsewhere in the Gangetic or Brahmaputra systems or from other regions with hydrological conditions which are essentially tropical. It would appear that by far the greatest number of migratory species in Bangladesh exhibit Category (ii) type migrations (FPCO 1992b). However, it has been suggested that the major carps migrate long distances even beyond the borders of Bangladesh, to spawn (Tsai and Ali 1985), but evidence of fry catches along the banks of the Padma suggest local spawning grounds given that there is little possibility for upstream migration because of the Farrakah Barrage just over the border in India. It is probable that the spawn is locally produced, as in the Kaptai River (Tsai and Ali 1985). The position of catfish in Bangladesh is least clear. The common catfish has been mentioned as migrating onto the floodplain and show movements of the Category (ii) type. The diafromous Hilsa shows large scale movements from the estuary into the river during the monsoon season, such as typical of Category (iii) migration.
Table 2 identifies the possible impacts of FCDI schemes on the fisheries production as a matrix of the alteration of the hydrology of the floodplain against the consequences of various environmental characteristics, fish behavior and fisheries production.
Reduction of flood extent will decrease the extent of the feeding grounds for the fish, with a consequent fall in production of the fisheries.
Reduction of flood depth may increase productivity of the aquatic environment and increase the availability of nesting sites for 'black fish' species; the effect of this on overall fisheries production in uncertain, but could well increase the productive potential of the residential 'black fish' species.
Restriction of river bank overspill will delay the inundation of the flood, which will disrupt the breeding cycles of 'white fish' species and decrease the distribution of 'white fish' hatchlings over the floodplain. This would have a major impact on the biodiversity of the fishery and an unknown effect on the productive potential of the fishery. In addition, restricted access to the floodplain through channels and regulators would allow application of more efficient fishing techniques, leaving the fishery more susceptible to overfishing and a consequent fall in long-term production.
Table 2: FAP Fisheries Production Impact Matrix (Source: FPCO 1992 b)
|
Characteristics |
Possible Impacts of Engineered Flood Control Mechanisms Affecting Fisheries Production | ||||
|
of existing situation |
Reduction of Flood extent |
Reduction of flood depth |
Restriction of river bank overspills |
Reduction of water throughput |
Drainage 'congestion |
|
Environmental capacity |
Reduction of flood-plain environment |
|
Delay of inundation of flood-plain |
|
Uncertain |
|
Water quality |
|
|
|
Increased risk of pollution eutrophication and deoxygenation |
Possible stagnation |
|
Ecosystem production |
Decrease in aquatic productivity. Loss of nutrient input for terrestrial production. |
Increase in aquatic productivity. |
|
Reduction of environmental production. |
Uncertain |
|
Land use |
Increase in cereal production. Increase in aquaculture opportunities. |
Increase in crop security |
Increase in crop security |
Degradation of land and water resources |
Waterlogging. Loss of agriculture |
|
Biodiversity |
Loss of aquatic and terrestrial biodiversity |
|
Loss of fish biodiversity; depletion of migratory species. |
Loss of biodiversity |
Uncertain |
|
Fish migration |
|
|
Loss of migration routes and decrease in distribution of fish hatchlings over the flood-plains. |
Degraded environment |
|
|
Fish reproduction |
|
Possible increase for nesting sites. |
Disruption of breeding cycles. |
Increase in natural mortality. |
|
|
Fish growth |
Decrease in feeding grounds for fish |
Uncertain. |
Loss of access to flood-plains; reduced feeding opportunities. |
Degraded environment, loss of feeding opportunities. |
|
|
Fish production |
Loss in production |
Increased production potential for "black" fish. Outcome for fisheries production uncertain. |
Increased susceptibility to capture due to restricted entry to the flood-plains through regulators and channels. Long-term reduction of fisheries production. |
Reduction in fisheries production |
Uncertain |
|
Environmental stability |
Short-term increase in stability |
|
|
|
|
|
Environmental sustainability |
Possible loss in sustainability |
|
|
|
|
|
Fisheries resource sustainability |
Loss in sustainability |
|
Increased susceptibility to overfishing |
Increased susceptibility to overfishing |
Uncertain |
Reduction of water flow through the flood control scheme will increase the risk of pollution and a consequent degradation of land and water resources, leading to a fall in production.
Finally, increased drainage congestion will increase the aquatic habitat, but the effect on environmental capacity will be uncertain, given the possible impact on water quality; the effect on fisheries production would therefore be uncertain.
It is possible to partially mitigate the negative impacts due to restriction of river bank overspill through structural addition and/or modification of flood control engineering. A number of structures, which might collectively be called fish passes or fish ladders, have been devised to circumvent engineering structures that obstruct fish movement. Normally, these are found in association with structures that are essentially dams which cut across the main flow of the river. Where barrages are planned that require a fish ladder for fish migrating upstream, the methodology for their design has already been developed. What is required is detailed knowledge of the physiology of the local fish involved and the design parameters of the structure. A fish pass design can then be tailored to a specific structure.
Dams and barrages are designed to maintain differences in heads of water far greater than the meter or so head deferential that may result from the flood control embankment engineering in Bangladesh. There are no main river structures intended to maintain water levels above the nature level. The concept of fish ladders to enable fish migrating against the current to surmount large permanent variations in water level is, therefore, generally not applicable in Bangladesh. Nevertheless, the principles used in the design of such structures are essentially the same as for the design of structures that allow the movement of fish onto the floodplain.
There is no experience of fish passes in Bangladesh and very little information on the swimming characteristics of the fish species involved. Those characteristics and the likely response to various types of fish passes will have to be extrapolated from information gathered in other parts of the world. Before the design and operational characteristics of a fish pass can be decided upon, those species of the migratory response which are being catered for need to be identified.
River discharge provides the essential directional clues to physiologically prepared fish to move upstream whilst also offering increased resistance to progress. Fish migrate normally at some intermediate cruising speed and only rarely at maximum speed. If current velocity in the main river channel exceeds their swimming ability, the fish will move closer to the bank where velocities are generally slower. The presence of turbulence or whirlpools tends to disorient the fish.
The concept for fish ladders, to enable fish migrating against current to Surmount permanent large variations in water level, is generally not applicable in Bangladesh, as there are no main river structures intended to maintain water levels above the natural level the common regulatory structures used in Bangladesh are the regulators with vertical gates controlling both the inflow of water into an area and the outflow drainage from it. There are normally situated across secondary rivers and drainage systems that traverse embanked flood control schemes.
Most often, the inflow of water is controlled by large undershot sluices, the gates of which can be opened between compartments and the rising river to allow controlled volumes of water into the cultivated area. The drainage sluices can be of the same type (undershot), but can also take the form of a large steel gate which opens automatically as the pressure builds up behind it. Simpler overshot gates can be used for the same purpose. The drainage sluices allow the evacuation of rainwater flooding from the compartment during the rains and allow the water level in the compartment to be finely controlled in relation to the inflow channels to facilitate rice cultivation.
These regulators and sluices can be modified to improve their 'fish friendliness', prevent fish kills, minimize physical harm to fish, and avert detrimental changes in their behavior.
4.1 Fish stocking and fish cultivation in burrow-pits
4.2 Aquaculture programme in ponds/tanks
4.3 Aquaculture in canals
4.4 Aquaculture in dead rivers/channels
4.5 Integrated fish-farming
4.6 Fish culture in paddy fields
4.7 Pen culture offish
In order to harvest the potential of aquaculture within FCDI projects, both FPCO and Ministry of Fisheries and Livestock (MOFL) have worked out various options for integration of fisheries development in FCDI projects. An innovative proposal suggesting fish culture in rice fields has also been proposed. This section is based on the proposals of MOFL (1993).
Burrow-pits, after implementation of irrigation, drainage and embankment projects, usually lie unused. Some fish which grow naturally in some of these pits are caught by poor people. These pits could be turned into nursery ponds and could be used for growing of quick-yielding species. Up to 1.25 million fingerlings per hectare can be produced by modifying the size and depth of these pits besides about 1.5 of high-yielding fish, like Sarpunti and Tilapia. The required rehabilitation includes earth excavation work and water control structures.
Before the flood control and irrigation projects were implemented, production of fish in ponds in flood-prone areas was very low. Aquaculture was risky because there was the possibility of inundation. Once flood control infrastructure was built, this risk greatly diminished. According to present experiences, about two tons of fish per hectare can be easily produced in ponds.
Aquaculture in the canals of the FCDI project is possible by maintaining suitable water levels, and providing some basic facilities without disturbing the irrigation programme. This would require setting up iron-nets or meshes at certain distances and establishing fishing management units. About 700 kg of fish per hectare can be produced in these canals.
Due to the construction of flood control structures, some rivers became closed or semi-closed waterbodies - for example, Dakatia River in the Chandpur Irrigation Project, the Ichamati River in the Panda Irrigation Project and the Kumar River in the Ganges-Kobadak Project. Polders of coastal embankment projects have turned hundreds of rivers into closed lagoons, like the baors of Jessore. Therefore, such methods of fisheries development as followed in ox-bow lakes may well be implemented in these dead rivers. About 500 kg of fish per hectare can be produced in such rivers.
Although integrated fish-farming is relatively new in Bangladesh, the concept and practice of integrated fish production with other rural and agricultural activities is not new outside Bangladesh. Integrated fish-farming has been practised for centuries in China. Integrated fish-cum-poultry is also much practised in Thailand and Indonesia. In Bangladesh, fish-farming can quite easily be integrated with other farm activities such as poultry-rearing, cattle-fattening and growing crops. The system could be highly profitable and economical if an appropriate technology and farm management system is established.
Growing fish in paddy fields is very popular in Indonesia and Thailand. About 23,000t and 90,000t of fish are raised by this process in Thailand and Indonesia respectively, This method of rearing fish is widely practices in Indonesia, where water is provided through canals to rice fields, ponds and pits. In Thailand the method is similar, although not as widespread.
During the rainy season, sufficient water is available in the paddy fields for about four to six months. During this time, the fish grow in a natural way. Suitable and quick-yielding species are cultured. These fish are netted from adjacent canals or lowlands where they move as water recedes at the end of the rainly season. About 300 kg of fish can be produced per hectare in this way.
In Bangladesh, there is a very good opportunity of rearing fish in paddyfields, particularly in paddyfields under irrigation schemes such as those of the Water Development Board this method does not require feeding the fish. Punti, Nilotica and common carps are not suitable for such culture. It is gathered from Indonesian farmers that fish raised by this method fetch much more profit than the rice grown in the same field.
Although pen culture technology is used in the Philippines on a subsistence or commercial basis, its application in Bangladesh is still on an experimental basis. Results from such trials have shown that pen culture is not only technically feasible but also economically viable under Bangladesh conditions. The advantages of using pens to grow fish in that the initial capital cost is low. The pens could be built by using locally-available materials like bamboo, rattan and wood. The expected yield is about 500 kg/ha/yr.
Water development in Bangladesh has arrived at a phase where it has to proceed progressively from easy-to-develop single purpose schemes to more complex inter-related projects. This implies the necessary plan for major infrastructure projects, that would unlock the hitherto untapped water resources of major rivers, as they would require longer development periods. Such a strategy, in no way precludes the continued development of easy-to-draw water schemes wherever feasible. The choice will have to be made among alternative technologies, competing and conflicting usage and allocation. This step, however, requires careful monitoring of the land and water sector so as to mitigate adverse environmental consequences from such development.
It is now recognized that the traditional FCDI projects are highly detrimental to the fisheries sector. Flood control embankments, over-drainage, and over-harvesting have been the main causes of decline in open fisheries. However, the potential of closed water fisheries are still to be harnessed.
The hydraulic structures used in FCDI projects should be modified to make them fish-friendly and fish passes should be introduced for easy movement of adults as well as juveniles. Inside already completed FCDI projects, extensive programmes of aquaculture may be undertaken. Fish culture in paddyfields would open up new opportunities in the fisheries sector.
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