One area where active conservation is taking place is the Chilaw lagoon; see map below.
Halfway up the west coast this is an area which was formerly mangrove forest. However, a great deal of it has been cleared for shrimp fisheries. Now an NGO, Seacology in cooperation with The Small Fishers Federation of Sri Lanka ( SUDEESA) are collaborating on a scheme to return sections of the lagoon to its former state.
This post is part information / case study and part an exercise sheet which can be adapted by teachers and students. I hope you find it useful.
the following are excerpts taken from online sources. Read through the following excepts re; Shrimp Farming in the Chilaw Lagoon
- The mangrove areas of Chilaw Lagoon have for a long time sustained the subsistence economies of the surrounding human communities, especially through provision of firewood, poles, posts, tanbark and also crabs, shrimps, molluscs and a variety of finfish for consumption. However, population densities have been steadily rising:
1971 350 persons/km2
1981 444 persons/km2
2009 506 persons/km2
- Unemployment levels are around 30% (2009)
- Self employment accounts for 30% of work force
- The population relies heavily on agriculture (23%) and fishing (16%)
- the fishermen and shrimp farmers use traditional boats; outrigger canoes amd log rafts but many don’t use boats at all, just nets
- most shrimp farms are relatively small employeing on average 3 or 4 workers
Shrimp farming did not start until the mid-1980s in the western coastal belt between Kalpitiya and Negombo, but there has been a rapid expansion in shrimp cultivation in recent years.The total number of farms in the Chilaw area has grown to 183 since 1993, when the CEA/Euroconsult survey estimated there to be approximately 18 farms in operation. This is a ten-fold increase on the numbers estimated in 1993. The area under cultivation in 1994 was approximately 52 hectares. In the 2001 survey it was estimated to be 247.8 hectares, nearly a 5-fold increase in a seven-year time-span.
Profits from Shrimp fishing are high but it’s ecological footprint is high; meaning a large area of lagoon is needed to sustain shrimp farming: estimates for the footprint put it at 27.86./ha.
One hectare of shrimp farm needs nearly 30 ha of lagoon to support it and keep it profitable. Overall the shrimp fiseries in the lagoon would require 2478 ha; much more water area than exists at present.
an area cleared of mangrove for a new shrimp fishery
The following important environmental consequences from shrimp farming:
- Valuable mangrove and marsh land rich in plant and animal life are cleared for pond construction and fringing habitats get heavily degraded. This leads to reduced feeding and breeding habitats for commercially important coastal and marine finfish and shellfish, to the detriment of the lucrative coastal fishery
- The operation of shrimp farms requires application of nutrients and chemicals (pesticides, lime). When discharged, these pollute the water, causing eutrophication, resulting in algal blooms (often toxic), severe oxygen depletion and high levels of fish/shrimp mortality.
- Hydrological changes and salinization of ground water occur when brackish water is pumped to shrimp farms situated more inland. Abstraction of ground water for fresh water supply to intensive pond culture may also result in salinization of fresh water aquifers, degrading domestic and agricultural water supplies, leading to social unrest.
- Intensive farming, where organisms are kept at high densities, requires hatchery seed supplies, supplementary feed and chemicals. On the other hand, the traditional extensive farming keeps the animals at low densities and do not require seed from hatcheries and supplementary feeding. However, extensive farming consumes the large areas of mangrove, with very low productivity in return.
- The construction of shallow ponds for shrimp farming is reported to have disturbed the drainage patterns in the area, resulting in the inundation of Chilaw and Puttalam areas during the heavy monsoon rains in 1995, adversely affecting over 3,000 households
- The self-pollution of the lagoon water contributes towards the spread of shrimp disease, reducing productivity, and increasingvulnerability to the shocks and stresses experienced by less wealthy farmers and has negative impacts on household income
- The clearance of mangroves also has an affect on the capacity of the lagoon to sustain the present levels of production in Chilaw. The cleaning capacity of mangroves will continue to be important to the productivity while the farms are dependent on lagoon water working in open-culture systems.
mangrove is valuable to shrimp fisheries in 3 ways
- nursery for larvae
- mangrove provides feed for shrimps
- mangroves can help filter out waste fromn the lagoon
An important feature in (Pambala-) Kakkapalliya is the recent establishment of the Small Fishers Federation of Lanka (SFFL), a non-governmental organisation (NGO) concerned with the well-being of the local fishing community, including their wives and children, and with eco-friendly projects and mangrove conservation
A mangrove rehabilitation project ran by SFFL, lead to the plantation of about 50 000 mangrove seedlings in Pambala Lagoon was inaugurated in 1997. The reforestation plots were visited in the field and estimated to cover about 2.4 ha.
The area required for lagoon water support is calculated to be 4.5 times the surface area of the farms. This means a lagoon water surface area of 1,115 hectares is required per year to support farming in Chilaw. This, perhaps, can help explain the problems the industry in Chilaw, Mundal and Puttalam has suffered from poor quality lagoonwater as a result of self-pollution
An alternative is the use of wetlands as a bio-filter for the effective removal of solidsand the transformation of excess nutrients.
Experimental constructed wetlands, usingplanted vegetation, have been tested successfully for treating effluents from freshwater catfish ponds in the USA, and for treating salt-water shrimp ponds in Thailand
The processes involved in suspended solids and nutrient removal in wetlandsinclude sedimentation, decomposition of organic matter, uptake of nutrients by plants and bacteria, nitrification-denitrification and absorption of ions by soil. Mangroves forests have also been reported as sinks of phosphorous and nitrogen and several authors have reported their effectiveness in removing nutrients from effluent water
The approach of combining shrimp farms and mangroves to act as biofilters, issupported by many environmentalists, as a positive move in the sustainable management of shrimp farms.
The benefits of mangroves as biofilters for shrimp farm effluents may be significant in areas such as Chilaw, where space is limited for the siting of sedimentation ponds, and the regeneration of mangroves may be beneficial to more interest groups than simply shrimp farmers.
Here, the replanting of mangroves, if managed effectively could benefit local communities for livestock fodder, firewood and traditional uses and fisher groups, as the presence of mangroves have been shown to increase shrimp fishery productivity in Chilaw lagoon
mangrove nurseries in Chilaw
Postscript; Check out: mangroves return to Chilaw Lagoon: http://ll.dw.de/en/mangroves-return-to-chilaw-lagoon/av-39532196
1.: Use the search facility on google (Chilaw Lagoon Shrimp Fisheries, shrimp ponds in Sri lanka ) to capture images of the lagoon environment, the traditional fishing outriggers and the shrimp farms; Use the images to describe the environment of Chilaw Lagoon
- Outline the factors which have led to the rapid expansion of shrimp farming in the Chliaw lagoon.
3.. What do you understand by the term eocological footprint (EF)? What is the EF for shrimp farming? Why is the ecological footprint of shrimp farming so high? How does this link to notions of sustainability?
4. Explain the ways in which mangrove conservation could be beneficial both to shrimp farmers and the wider community in Chilaw lagoon
5. Using the following resource links:
- the Guardian report see below
Outline the role the of the local community and especially the role of women in bringing about a more sustainable use of the lagoon resources.
- Effective Management for Biodiversity Conservation in Sri Lankan Coastal Wetlands: a measurement of the ecological footprint of shrimp farming in the chilaw lagoon area.