Abstract
The impacts of shrimp farming on water quality parameters and the effluent loading
in the Southwest (Khulna) and Southeast (Cox's Bazar) regions of Bangladesh was
investigated. A considerable amount of information about typical changes of
ecological parameters including nitrogen and phosphorus (eutrophication) and
solids (siltation) was collected. About 12 different water parameters were
continuously monitored from shrimp farms of both regions in year 1, then
investigations were concentrated in the Southwest region. A large shrimp farm
Soladana farm having both inlet and outlet was thoroughly studied in year 2 for
water quality monitoring and quantification of effluent/nutrient loading. The effects
of farm size on production and economic returns of marine shrimp (Penaeus
monodon) was investigated in year 3. Large fluctuations in temperature and salinity
took place during a production cycle and those may create unfavourable living
conditions for shrimp. Stress inducing temperature levels up to 38-39°C were
observed in farms of Khulna region. Salinity levels down to 0.6-1.0 ppt were
observed, which were far below the recommended level. Sub-lethal levels of
ammonia were occasionally present and may create stressing conditions. Except for
the final sampling, the concentrations of phosphorous and nitrogen were
consistently reduced in farm i.e. conc.inlet>conc.outlet. Total solids were always
higher in the intake water and deposited in farms during production cycle except for
harvest time. Eighty to ninety percent of the estimated nutrient input to the farm
was apparently trapped in the culture system. It was estimated that around 0.63 kg
nitrogen and 0.26 kg phosphorus were trapped in the shrimp farm sediment for
producing only one kg of shrimp. Around 514.2 kg/ha/cycle total suspended solids
(TSS) were accumulated in farm. Partial mass budget in the same large farm
indicates that the extensive shrimp culture systems in Bangladesh produce less than
1,000 kg/ha/year, do not pollute surrounding water and act as a sink for nutrients
and solids. The water quality in farms could not be controlled by farmers and was
mainly influenced by the quality of inflowing water. The highest survival (49%)
and production (204 kg/ha) of shrimp was recorded in small farms, while large
farms had the lowest survival (17%) and the lowest production (83 kg/ha). The
small farms were easier to manage, had higher abundance of plankton and lower
concentrations of harmful ammonia nitrogen compared to medium and large farms.
The study on mangrove forests showed that a total of less than 2% of the total
mangrove area of the country was found denuded due to shrimp farming and the
area of the Sundarbans remained unchanged from 1975 to 2001. However, a small
patch of 108 ha was encroached by local people for shrimp farming before 1975.
The Chakaria Sundarbans (8.540 ha) has been totally encroached for shrimp
farming. The production of shrimp in the cleared area is gradually decreasing due to
increasing soil acidity and decreasing litter fall in the area. An area of 133 ha of
mangrove forest of Jaldia island near Teknaf along the Naf river has been denuded
for shrimp farming. and 667 ha near Naf river at Anjumanpara of Panlongkhali has
also been denuded and used for shrimp/fish cum rice culture by rotation.
The study on socioeconomic impacts of shrimp farming revealed that shrimp
farming and related activities helped the concerned people to increase their
household income. which led to have more savings and investment resulting in
better livelihood and socioeconomic condition. Shrimp farming has contributed to
poverty alleviation through creating employment opportunity. The emergence of
commercial shrimp farming and the related backward and forward linkage activities
has opened up new dimension for women's involvement in many activities. Shrimp
processing factories and depots are the largest source of employment for women.
Expansions of shrimp farming play significant role to the development of roads and
communication, electrification, marketing systems and to improve overall economic
condition. However, unplanned development and poor management of shrimp
farms has created some negative impaets. Conflicts of land use have arisen between
shrimp farmers and land lessors. Commercial shrimp farming caused an uneven
distribution of income to the farmers and labourers. The access of local fishermen
and other poor people for open water fishing in shrimp farming areas has been
reduced. Coastal shrimp farming has both positive and negative impacts, however
there is a trade off towards the socioeconomic benefit, which is relatively higher.