M/S. Development Consultancy Services Ltd. and M/S. Engineering Consultancy Services Ltd. have been entrusted by Food and Agriculture Organisation of the United Nations through an agreement executed on 18 March, 1983 to undertake Tidal Area Study under Fisheries Resources Survey System. The project work was initiated from April 1982 on mutual understanding.
This report is the result of consultants undertaking of field survey on hydro-biological, soil, agro-aquacultural economy and collection and compilation of data from different agencies.
The objective of the study is to create a data base for tidal area resources for determining the comparative use on the tidally inundated land for agriculture, fisheries or a combination of these. For this those specific areas were selected for survey.
Polder 1 & 3 of Satkhira.
Chakoria Sundarban Area in Cox's Bazar.
Khepupara thana area in Patuakhali.
The scope of works for the study are as follows:
Collection of relevant existing data, maps, charts, etc.
Collection of reports and publication on fisheries, soil and Agriculture, climate and hydrology, socio-economic. etc.
Collection and analysis of field data on investigation, survey and sampling on hydro-biological, soil, agriculture and agro-aquacultural economy.
Analysis os climatological and hydrological data.
General assessment of
Soil and land potentialities of the tidal area.
Effect of salinity on soil for paddy.
Effect of shrimp culture vis-a-vis rice.
Within the perview of the survey, three areas were selected by the FAO, for the sample survey. These areas are :(1) Polder-I and Polder-III in Satkhira sub-division where presently shrimp culture is being practiced in paddy field. (2) In Chakaria Sundarban Area in Cox's Bazar sub-division where shrimp culture is being practiced by deforesting mangrove forest. (3) In the Khepupara thana area of Patuakhali district where shrimp culture is not being presently practiced.
Extensive areas of low lying land in the tidal zone of the southern Bengal are flooded with saline water as well as by direct rainfall. The area roughly parallels the Bay of Bengal along a strip 330 miles and verying in width from a few hundred feet to over 50 miles.
For many years, under Zamindari system, areas were protected with small dwarf embankment (bherry bund). Zaminders or the big land owners undertook the responsibility to construct & maintain the dykes to protect the land. Zaminders gave life-long lease to the tenant farmers who paid a part of their income of paddy production to the Zamindars. However, the fishery rights were excluded from the land lease and were leased out to the highest individual or the group bidders. Fishermen were engaged to perform the operation including fish harvesting.
Paddy cultivation in rotation with fish production were the main activities of the people of the area. The procedure adopted was as follows :
During rainy season tide water were introduced in the area by cutting the bherry. Fish laden water were retained in the creeks and trenches travesting the paddy field. During rainy season fish spread all over the area finding extensive grazing ground on the flooded paddy field. The fish were prevented from escaping from the bherry areas by fixing grating made of split bamboo fence across the wooden sluice gate.
Fish harvesting used to be done by draining rain water. Fish harvesting started in August and continued upto December. The land remained fallow till advent of monsoon. Since then the same procedure was followed. With the arrival of monsoon, gaps in the bherry were closed. Rain water retained in the paddy field until the whole area was covered with vast sheet of water. During the rainy season, the surrounding river water is comparatively sweet and occassionally the water is exchanged to bring down the salinity within the permissible limit for paddy cultivation. The field were then planted with paddy seedlings. Normal production of paddy was 10 to 20 mds. acres. (M.H. schuster) Yield of fin fish and shrimp were said to be 6 mds./acres.
Dykes constructed by the Zamindar were of inadequate section, low quality and required continuous maintenance. Dykes often collapsed due to hydrostatic pressure and errosive action of wind and current. Drainage facilities provided were also inadequate.
After abolition of Zamindari system in Bangladesh, the Govt. undertook the responsibility to construct the Coast. Embankment project through the U.S.AID assistance. Implementation of the Coastal Embankment Project started in 1961.
Coastal Embankment project extends over an area of approx. 5000 square miles in the Khulna, Bakherganj, Noakhali and Chittagong district. The majority of the area lies within the delta of Ganges-Brahmaputra-Meghna-Matamuhuri river system and has been formed by the sedimentary deposits in recent times. The lands within the project area were subjected to saline inundation and flooding during portion of the year or round the year depending on location and elevation.
The low lying areas are interlaced by an intricate rivers and tidal channel system which cuts the land into numerous segments In the decade 1960–70 a large programme was undertaken to empolder the individual land masses with earthern embankment known as polders. In the process of construction large number of streams were closed off from their former connection with the networks of coastal streams.
The coastal embankment scheme was intended to increase the agricultural production by preventing the saline inundation, reducing the flooding and preserving sweet water in the internal channel system.
Effects of the river confinement and future land use pattern were not taken into consideration at the planning or implementation stages of the project. Century long practice of fish cum paddy culture in the low lying areas were stopped. Although it was acknowledged that the fish industry has been affected in the project area by polder construction (evaluation report) but no action was taken or advised to provide necessary infrastructure for promoting the fish production.
An important consequence of the river confinement was the rapid river siltation. This problem was very much pronounced in the western zone of the delta. Channels in this area was maintained by the inflow and outflow of tides in and from the surrounding land mass. Eventually, the entire river system started dying when the spilling was prevented. Drainage sluices provided in the embankment failed to operate due to sedimentation in the river. Crop land were inundated due to rainfall during monsoon for failure of the flap gates provided in sluice. Automatic flap gates installed with the regulators were buried with the mud, as a consequence of siltation. It failed to operate automatically to drain out accumulated rain water due to deposition of silt and the low lying areas with the polder are virtually being turned into man-made lake during rainy season preventing cultivation of crops. Even if it would have been possible to plant the crop depending on the weather condition but at any stage during the cultural period always there is chance of large scale major inundation of paddy plants due to heavy drainage congestation.
The confinement by embankment prevented over bank flow of silt laden water into the polders from the rivers and this also affected the reclamation of low lying areas. Rapid siltation of the rivers and channels has also greatly damaged the fishery potential of the area and the livelihood of fishermen.
There are very large potentials for developing coastal aquaculture in Bangladesh. The extensive tidal lands provides excellent condition for water control, good tidal range, conducive temperature regime and high production of phyto and zoo plankton. Depending on the above echological condition, it was therefore, obvious that the brackish water aquaculture involving shrimp and fin fishes has been practiced for long time in Bangladesh. The century long practice of this culture was blocked due to the construction of coastal embankment. However, towards the later part of 70, the shrimp cultural activities gained its momentum owing the high value of shrimp in the World market and demand for fin fish for the domestic consumption. Poor agricultural output on the paddy field vis-a-vis attractive financial return from fish culture induced entrepreneurs to cut open the BWDB embankment for introducing saline water in the poldered land.
Coastal embankment project has created a situation favourable to the spread of brackish water shrimp and fish culture in the area In the sixties the price of frozen shrimp was so low that it did not attract the attention to start the culture disowing the ban imposed on entry of saline water in the poldered areas. However on a small scale the fish culture continued on narrow strips of land between the newly created embankment and water edge by taking lease from the Water Development Board.
The increased demand of shrimp and comparatively high export price attracted the entrepreneurs and the land owners to defy the imposed restriction on entry of brackish water into the polder. As a result, shrimp farming inside the polders during dry season was reactivised in the low land where facility existed to provide water exchange through regulating arrangement.
The traditional bherri operation is the coastal areas prior to C.E.P. and the present day shrimp culture practice has a basic difference.
For bherri operation, water was introduced is the paddy field during monsoon when water turns more or less sweet or losses salinity, Fish and paddy were cultured simultaneously.
Under the present system of shrimp culture is Khulna area, saline water is taken during January and February and inundation and exchange of water is continued throughout the shrimp culture period.
Many observer consider that shrimp culture is replacing T. aman. This is partly true. In the western belt of Khulna district, poor drainage facility from the poldered area inadequate rainfall during crop season, specially lack of supplemental irrigation supply during drought period is not at all conducive for growing paddy. At times high rainfall creates serious drainage congestion and submerges the rice crop. General trend in that area is to go for year round shrimp and fish culture which is economically more prospective than the paddy cultivation which is considered as a risky crop.
Shrimp culture activities gradually encroaching the paddy field in the poldered area of the belt. Land used for shrimp culture in this belt vis-a-vis the poldered area is tabulated below from 1981 to 1983.
| Polder No. | Total Area in polder. | Shrimp Culture Area in Acres | Total Area. | ||
| 1980–81 | 1981–82 | 1982–83 | |||
| No.I | 70,100 | 5,120 | 5,568 | 5,980 | |
| No.2 | 33,725 | 91 | 266 | 482 | |
| No.3 | 45,400 | 2,843 | 6,120 | 8,286 | |
| No.4 | 24,225 | 828 | - | 53 | |
| No.5 | 1,36,900 | 405.50 | 378 | 1,663 | |
| Polder 6–8 | 60,705 | 40 | 182 | 1,121 | |
| 3,71,055 | 9,377.5 | 12,514 | 17,589 | 4.74% | |
Above table shows that only a scanty portion i.e. 4.74% of the gross poldered area is occupied for shrimp culture. Rest of the area barring homestead land is still used for ra infed paddy culture.
Poldered area in Khulna sub-division is not yet facing drainage problem as found in the western belt of Satkhira. Shrimp farming in rotation with T. Aman is reported to be widely practiced in Khulna sub-division. Most of the shrimp/prawn. fish culture activities are seasonal and at present taking place in the season from January to July when the condition are not suitable for T.Aman cultivation.
By mid July the fish is harvested and the ponds are drained out. The remaining fish if any are taken in the internal channels and creeks and are allowed to grow there: The ponds are now dried, ploughed and transplantation is started.
Transplanted Aman Cultivation in rotation with shrimp has several complimentary advantages:
During harvesting of paddy, the corns that drop down and the remains of the paddy plant stem forms food for the periphyta by bacterial decomposition. In turn these periphyta are the food for the shrimp.
During shrimp culture, the molted shells of shrimps and the metabolite load enriches the soil through mineralisation and helps organic fertilisation of the soil for paddy culture.
Sediments deposited during water exchange for shrimp culture, enriches the soil for paddy culture, sediments deposited also gradually reclaims the land and leads to improvement of drainage although over a long period the land will thus go out of shrimp culture.
During shrimp culture period, the land remains under saline inundation and as a result the weeds remain controlled. Also less number of ploughing is necessary (normally two ploughings instead of four ploughings when fish is not cultured) during transplantation of Aman paddy. Subsequently effort of weeding required is also minimal.
The area of Chakaria Sundarban is within the delta of Matamuhuri River. In response to the increased public demand some 1900 ha of forest land has been leased out to 40 private parties. After obtaining the lease from the forest department dykes were constructed and wooden box sluices installed.
There is general misconception that Chakaria Sundarban area are being cleared by public for developing shrimp fisheries. This is possibly not the case.
For whatever reasons, Chakaria Sundarbans forest started detereoration long back and the land as a forest land was not producing its expected yield. Since, the land was lying fallow, some enthusiastic fishery enterpreneurs managed to obtain the lease through fishery department.
Either of the following two reasons or a combination of the two caused destruction of the forest.
Because of high demand of fire wood, for salt production in the past, indiscriminate falling of trees caused ultimate destruction of the forest to its present state. Since most of the area is above the general tide level during dry season, when the salinity is optimum the area is not suitable for a natural habitat of shrimp.
With the gradual deposition of silt, the land elevation became higher and higher so that land is flooded only during monsoon and the water being comparatively sweet during this season, is not favourable for sustaining mangrove forest.
The Matamuhuri basin and the Cox's Bazar area is characterised by the higher rainfall intensities. Flash flood in the Matamuhuri river causes sudden drop down of the salinity which restrict the proper growth of the shrimp. At times the mortality rate is also high.
The forty private parties who have taken lease of land for shrimp culture grow shrimp only during the period from May to October. During remaining period of the year the tidal range do not permit gravity inundation of the land.
The fish culturist have built up their own dyke system and installed indegenous wooden box culverts and pucca structures. After harvesting of the shrimp the land remain fallow and dried from December to Feb./March. Then as the tidal height gradually rises the ponds are inundated and shrimp starts growing.
It has been assessed that year round shrimp culture is possible in Chakoria Sundarban area by installing low lift pumps. Preliminary estimate shows, five nos. of 2 cusecs low lift pumps can provide adequate inundation and water exchange for year round shrimp culture economically for 50 ha. plots.
Table below shows soil characteristics of Rampur Area:
| Rampur | Mechanical Results of Soil Sample. | ||||
| Depth | % Sand | % Silt | % Clay | P.M. Value | Textural Name |
| 0 | 2.8 | 62.10 | 35.10 | 4.7 | Silty clay loan |
| 1 | 3.7 | 60.5 | 35.80 | 4.2 | do |
| 2 | 4.8 | 59.6 | 35.6 | 3.9 | do |
| 3 | 6.2 | 58.10 | 35.7 | 4.1 | do |
| 4 | 5.8 | 59.30 | 34.9 | 3.3 | do |
| 5 | 7.10 | 57.80 | 35.10 | 3.1 | do |
Textural composition of soil is silty clay loam and is highly acidic. The land will not be suitable for ordinary agriculture practice without costly and a long drawn process of land treatment.
Shrimp culture is relatively new introduction in Chittagong district. At present, it is located around Cox's Bazar area, from Bashkhali South to Teknaf, Moheskhali island and in Chakaria Sundarban area. Most of the shrimp culture is taking place on salt drying bed during the monsoon season (May to December) when salt production is not possible.
Salt production was once widely practiced in the Coastal Region but now is mostly in the central area of Chittagong District.
For salt cultivation pond is errected in tidally inundated land with small embankment and the salt water is introduced in the pond during dry season where it is evaporated by sun-shine and the crude salt is produced. Some polders in the tidal lands are at present also being used for salt production.
For shrimp culture pond is inundated to hold the water to a depth of 3 to 4 ft.
Before the construction of Coastal embankment in the region the individual land holders constructed redimentary embankment to protect their agricultural land from saline water. At that time salt culture was practiced outside this embankment and the area was limited. Due to lack of proper maintenance of the embankment the saline water inundated the agricultural land. Subsequently the low elevated agricultural lands with the dilapidated embankment was utilised for salt production. After the construction of coastal embankment, the salt producers living inside the embankment continued to do the business as before by taking sea water though the sluice or cutting the W.D.B. embankment. About 13000 hectares are at present used for salt production.
Effect of Shrimp Culture on Paddy
There are a few complimentary beneficial effect on T. Aman cultivation in rotation with shrimp as has already been stated in Chapter-3.2. However, there could be a few adverse effect also as enumerated below:
Shrimp pond operation is different from bheri operation for fish culture in rice field as used to be done prior to present day shrimp. Shrimp fields are kept constantly under saline inundation and as such before going for transplantation of paddy seedlings, the ponds soil has to be very carefully leached out. In years of drought. This may be difficult as rainfall will be scanty and river water will still remain highly saline.
The leasee for shrimp and rice cultivation are different groups of people. With high price of shrimps, the leasee for shrimp may easily influence the land owner to delay the harvesting of shrimp for increased yield. But this will affect the paddy cultivation, if the water in the pond is not timely drained out and land vacated for transplantation.
Shrimp culture is less labour intensive. If the lands gradually goes over to year round shrimp culture, the employment opportunities will decrease, and income redistribution will be a problem. Only a few will be benefitted by shrimp culture.
Presently shrimp-cum-paddy culture is being done within the polders at more or less scattered locations. Since the setting of the shrimp fields are not properly planned, the adjoining paddy field areas where shrimp is not cultured, the paddy fields are affected due to seepage and percolation of saline water from the adjoining shrimp field.
Effect on Livestock
With the gradual extension of shrimp fields and encroachment in the homestead areas, the following adverse effects are being noticed.
Grazing ground for cattle heads are fast diminishing.
Sweet water for stock feeding and domestic consumption are becoming scarce.
Both these adverse effects will lead to decrease in cattle population.
Effect on Forestry
For whatever reasons, the Chakaria Sundarban is fast dying out and the land is being occupied by the shrimp farmers. Instead of making an effort to regrow the mangrove forestry, any unplanned shrimp farming is likely to accelerate the destruction of the highly productive mangrove eco-system, Planned extension of shrimp farming with provision of regrowing mangrove forest in between shrimp fields and foreshore area will be a highly complimentary and productive system.
In areas other than forest every village home has a backyard/ encircled garden of trees. Gradual encroachment of the homestead areas by shrimp farms are likely to adversely affect the domestic plants, fruit trees, vegetable gardens and create problems for availability of fire wood.
Dwarf embankment is constructed or repaired around the paddy field in December or January just after Aman harvest is over. The enclosed area is locally called ghers ranges from 5 acres to 550 acres. Wooden Box sluices (3'×3') are installed by cutting the BWDB embankment. Nos. of wooden sluices required for water exchange depends on the pond area. When the embankment and water control structures are ready, fish laden water is taken into the pond. Flooding the field continue in each successive spring tides until water depth reaches to 2 to 3 ft. Inundation of the field with postlarval and juvenile shrimp as well as fin fish generally starts in Khulna district from January. The shrimp and fin fishes are left to grow and mature. Normally they feed naturally occuring food phyko-plankton, zoo-plankton and algae etc.). Seldom additional fish meal are supplied.
Harvesting of different varieties of small size species of shrimp starts from March. Generally M. bevicornis and M. monoceros are harvested in March and April and P. monodon at a later stage in month of May. Peak harvesting time of P. Monodon is in the month of June. It was observed that with supplemental stocking the harvesting season can be continued upto September.
When in rotation with T. Aman fishing generally continues upto end of July. With the advent of monsoon rain, salinity in the river decreases and by August river water almost loose salinity. By this time significant amount of fin fish are caught, water from the field is drained, remaining shrimp and fin fish are kept in low lying areas and in the channel of the field. The fields are now ready for T. Aman transplantation in August. Salinity from the paddy field is washed out by progressive replacement of less saline river water during the process of catching fish. Rain water also washes out the salinity of the field.
The method of shrimp harvesting at present practiced is the traditional trapping method. Most common practice is to trap in a basin near the sluice gate/wooden box sluice by means of fence made from split bamboo screen. With the fall of tide level, water level in the river becomes lower than the field, the box sluice is opened and water starts draining from the field. The shrimp that are already adult follow the flow of water and as a result are trapped in the basin and harvested by means of cast nets. Sometimes the nets are dragge through it. The shrimps have natural instinct to respond to the flow during new and full moon phases. Tide water is exchanged as the tide goes on.
The harvesting continues during day and night. Some farmers perform the catch during day to safeguard and for prevention of theft by the workers. Fishing continue around 7 to 8 days in each spring tides. For rest of the month fishing continues but the yield is too low in comparison to harvesting figure during spring tides.
The field is then prepared for T. Aman cultivation and the transplantation of T. Aman then starts by August. Occasionally the paddy area is flushed with river water through regulator/box sluices to supplement the water requirement for the paddy in case of drought. Recently survey conducted by the Delta Development Project authority around polder 22 in the Khulna area reveals that the transplanted rice suffers little or no damage if the rainfall is adequate and the distribution is regular throughout the period.
Low tide level around Khulna and Satkhira area during February and March limits greatly inflow of post larvae and Juveniles through the incoming tide water when they are most abundant in the river. The tide level gradually increase and by June it reaches a higher stage. Still then a good number of Juveniles and post larvae are available in the river and the water exchange is highly favourable but for the curtailment of the growing season due to paddy plantation sufficient time are not left for them to attain maturity. To avoid this difficulty, most of the shrimp culturists have now started supplementary stocking of shrimp juvenile.
From the recent survey it has been observed that the availability of the post larval and juveniles are scare in the upper region of the Satkhira due to trapping in the down stream reaches of the river. As a result supplementary stocking is being widely practiced in the area by purchasing the fry from the gatherers. Stocking in almost all the gher continues upto June. Considering the economical gain, the culturing period is extended by the shrimp culturist upto September - October. Data collected from the pond harvest during the period indicated that a high proportion of shrimp are catched during August in some pond although the salinity level comes down to a permissible limit for paddy culture. Greater attention is not being paid to continue the P. Monodon harvest so long it is available.
4. In Cox's Bazar Area
In Cox's Bazar area, salt production starts in higher elevated land from December and continued upto April. Salt is produced by using solar energy. After salt production, the land is utilised for shrimp culture.
The land elevation permits entry of water in full and new moon phases. During ebb tides water entry is facilitated in the low areas and creeks. Fish culture is also practiced in the creeks and low contour land through out the year.
Water is introduced in the pond through main sluice gate owned by BWDB. Besides this gate land owner constructed sluice gates along the pheriphery of the embanked area.
Shrimp culture is being practiced by stocking the fry introduced and nursed in the pond with fry laden saline water. Occassionally, shrimp juvenile are stocked in the pond, collecting from the surrounding rivers. Recently, trend has been developed to introduce the water initially in a nursery pond, and screen the predetor in the pond by netting. Subsequently, Juveniles are introduced in the main pond by opening small wooden gate fitted in the nursery pond.
The area is located in the zone of higher rainfall intensities and as such, sudden flash flood in the river is an usual phenomennon. Rainfall also causes sudden dilution of salinity in the pond water. Abrupt changes in the salinity of pond water and as well as in the river water used for tidal manipulation causes high mortality rate of shrimp. Acid-Sulphate problem in the soil is also a major factor for low production of shrimp.
Production of P. Monodon continues through out the year with the peak occuring in October and November. Catch of fin-fish is about the same of P. Monodon by weight. Harvesting peak period of fin-fish coincides with that of P. Monodon Presence of M. rosenburgi is insignificant in the catch. However, the quantum of the different species of shrimp catch is substantial in relation to Satkhira area.
Although the culturing period of P. Monodon including other species extends through out the year but the production rate is lower than in Satkhira area both in terms of quantity and in value in consideration of unit area cultured. The reason for the low production may be attributed to non adoption of supplementary stocking practices, sudden dilution of salinity caused by heavy rainfall and acid sulphate problem in the soil.
