Global warming, sea-level rise and a series of resultant changes in the coastal, as well as the inland aquatic environment should no longer be taken as mere conjectures of some scientists; these are now appearing more and more as stark realities. Bangladesh is one of the countries which are feared to be drastically affected, and that too relatively early, because of its vulnerable geographical position and low land elevation. The scientists predict that in Bangladesh vast low-lying coastal areas, measuring nearly one-third of the country -- will go under the rising sea water much before the end of the current century.
As a matter of fact, signs of sea-water rise and the resultant salinity intrusion, affecting paddy yield and horticulture in the coastal districts, are already being observed. Some sweet water rivers, including the Madhumati, that flows through Gopalganj or the bordering Narail and Faridpur districts, have become perceptibly saline causing concerns to the agricultural farmers. The water of these rivers in dry months is often not suitable for agricultural irrigation or drinking.
The impact of rising salinity is not limited only to agriculture; it extends to fresh water fisheries also. Occurrences of brackish water aquatic fauna, which were once a rare phenomenon or totally unheard of, in the upper reaches of the Madhumati and many other sweet water rivers, are becoming increasingly common. The frequency of tidal surges, in the form of Sidr, Nargis, Aila etc. is on the rise. The people, even the common rural people, no longer disbelieve that major changes are taking place in Bangladesh environment, and more frequent natural calamities in different forms are likely to occur in the future.
The scientists, policy makers, planners and our development partners - all realise that precautionary or adaptive measures at local and national levels are to be taken without delay so that the people can suitably adapt their living, housing, agricultural and aquaculture practices and all other activities to the predicted and already experienced environmental changes.
SOME PREDICTED ENVIRONMENTAL CHANGES AND THEIR IMPACTS: Some of the more apparent effects of global warming on aquatic environment in Bangladesh and elsewhere are as follows:
Temperature increase in the aquatic environment: This parameter may produce the following impacts on the aquatic fauna:
* Quicker physical growth
* Early sexual maturity
* Changes in the reproductive cycles
* Impact on the number of eggs and size of the eggs and the young ones
* Migration to areas of preferred temperatures
* Changes in the spawning grounds
Rise in sea-water level and the concomitant salinity rise in the inland waters: Gradual rise in sea-water level will slowly lead to a series of changes in the coastal wild fisheries, aquaculture and agriculture:
* Progressive upstream ingression of salinity will affect agriculture and terrestrial and aquatic flora and fauna
* Fresh water aquatic fauna and flora will be pushed more and more upstream
* Brackish and marine flora and fauna will be gradually replacing the fresh water species from the downstream to more and more upstream
* Galda shrimp spawning grounds will be shifting northwards or upstream
* At least some of the carp spawning grounds will be pushed upstream from their present positions in the Halda and possibly some other rivers
* Progressively higher and higher inundation of and disruption to the low-lying mangrove areas and growth of new mangrove swamps northward are likely to take place
* Along with the disruption to the low-lying mangrove covers, hazardous consequences will take place in the existing nursery areas of commercial shrimp and many species of marine fish and other aquatic fauna
* Shifting of shrimp and fish nurseries upstream with the progression of mangrove covers upstream will inevitably happen
* With the rise in sea-water level and progression of saline water upstream, a gradual shift from fresh water aquaculture to brackish water aquaculture can be logically expected
* With progressive rise in the sea-water level and the resultant inundation of the southern land masses, (i) structural changes in the existing aquaculture infrastructure, (iii) changes in the culture technologies and (iii) shifting of aquaculture infrastructure from south to north will be inevitable
More frequent monsoon floods of longer duration: Higher atmospheric and sea-water temperatures accelerating sea-water evaporation and formation of more clouds than in the past, are likely to result in heavier and longer monsoon on an average. With this, coupled with the rising sea level, the following conditions may be expected:
* Monsoon runoff water in the inland areas will take longer and longer time to drain out into the sea
* More frequent and longer duration monsoon floods
* Stagnation of water in extensive low-lying inland areas, in addition to the traditional floodplains
* Reduction in the agricultural land area
* Increased unemployment in the agricultural farming sector
* More and more efforts to significantly intensify agricultural production in the gradually shrunken agricultural land
* More and more dependence for employment on capture and culture fisheries
FLOODS, AN ADVERSITY, CAN BE USED AS AN OPPORTUNITY:
Fishery can harness benefits from floods: Floods in Bangladesh are a recurrent natural phenomenon and cause heavy damages to all sectors of the country's economy. Floods are traditionally considered as a curse - a source of immense destructions and untold human adversities. But just cursing the floods and the sea-water rise will not help us. We should better courageously face the inevitable environmental changes and find out ways and means to utilise the sea-water rise and the floods as opportunities, rather than taking them as a source of only destructions and miseries. Fisheries offer a unique opportunity to harness large socio-economic benefits from the floods, transforming the curse into a boon or asset. Intelligent use of the flood water through organised fish production on a large scale, involving the rural people, including those displaced by the floods, can create immense opportunities and benefits for the people and the country as a whole.
Some initial efforts with promising results: Driven by the need, many people have already initiated efforts to make use of the floodplains and rivers through aqaufarming using pen culture and cage culture (net, wire mesh or bamboo split enclosures). One could see crude forms of pens in deeply flooded paddy areas, dead or seasonal rivers, haors (floodplains) and (baors) ox-bow lakes in various parts of the country. The technology consists of enclosing a part of the floodplains or a stretch of a stagnant or a slow moving river with some kind of fencing materials, stocking large-size fish and prawn fingerling in them, providing the young fish and shrimps with suitable feed stuff and then harvesting a full crop of high-priced fish and prawn in five to seven months' time. Production of 3-5 MT of fish/Ha is not uncommon and the production rate can be significantly increased. In cages, placed in slow moving perennial rivers, fast growing tilapia production, in excess of 50 MT/Ha, has been demonstrated in certain places.
SOME SUGGESTIONS FOR FUTURE PLANNING:
* Mapping of estimated inundation line and depth as a result of gradual sea-level rise up to 2050, at 10-year intervals
* Determine the best suited species for coastal aquafarming in response to the salinity increase
* Determine suitable farming practices to integrate coastal aquafarming with agricultural farming
* Identify and bring in from wherever possible paddy varieties and horticultural species having higher resistance to salinity
* Monitor salinity ingression in the strategic rivers and the floral and faunal changes in them
* Monitor the changes in the breeding grounds of Galda and Bagda shrimps and exportable crabs and take measures to conserve them
* Monitor any changes in the breeding grounds of the major carp species in the Halda river and other rivers which are likely to be affected relatively early
* Identify and demarcate suitable areas in the floodplains, dead rivers, slow moving rivers where pen and cage culture technologies can be employed involving rural people
* Identify environment and technology-specific culture species, giving adequate attention to the need for using seasonal waters for fish farming and new employment creation
* Organise rural people into farming groups and demonstrate pen and cage culture of brackish water and fresh-water fish, shrimps and crabs in the coastal and inland floodplain areas as models of community-based aquaculture development in non-conventional aquaculture areas
* Identify suitable pen and cage materials for brackish and fresh waters and their sources of availability
* Produce feed suitable for various culture systems
* Identify future sources of drinking water in the coastal areas, already affected or to be affected by salinity ingression
* Develop specific pathogen-free Galda and Bagda shrimp broodstock and fry
* Refine technology for large-scale introduction of fast growing 100 per cent pure mono-sex tilapia
* Carp breeding area conservation
* Carp broodstock improvement
* Introduce and enforce hatchery and feed certification system to ensure their quality and food safety
Mahmudul Karim, PhD is with the Bangladesh Shrimp and Fish Foundation.
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