Contents - Previous - Next

This is the old United Nations University website. Visit the new site at

7. Ecological and socio-economic aspects of environmental changes in two mangrove-fringed lagoon systems in southern Sri Lanka

A. T. Mahinda Silva

Sri Lanka, with a coastline of about 1,700 km (fig. 1), has numerous coastal lagoons, with a total area of about 122,000 ha (Sivakumar 1980). About a third of these lagoons are shallow, with extensively developed tidal flats, mangroves, and salt marshes. The rest are relatively deep, though often fringed with mangrove forest or salt marsh. The mangrove resources of Sri Lanka are largely distributed through these coastal lagoons and on the shores of inlets and sheltered embayments around the coastline. Although people do not live in the mangrove areas, there are many villages and towns close to them. The mangroves have long been used as a source of timber, charcoal, and fuelwood and have provided an environment that sustains fisheries and shellfishing.

A recent research project, sponsored by the United Nations University and structured and carried out by the Marga Institute of Colombo, studied environmental changes, ecological conditions, and sociological aspects of two coastal lagoon ecosystems in southern Sri Lanka (Fernando 1985, 1986). Results of these studies provide a basis for a local assessment of the role and relationships of mangrove ecosystems in the ecology, livelihood, and economic development of people living in this coastal region.

The two lagoon systems are Rekawa and Kalametiya (together with the adjoining Lunama), in the administrative district of Hambantota on the south coast, south of the main coastal highway, east of Tangalla (fig. 2). Rekawa lagoon (fig. 3) is an estuarine system within which, until recently, sea water has been diluted only by relatively small runoff from the land. Kalametiya lagoon (fig. 4) was once similar but has been freshened in recent decades by the inflow of water draining from an irrigated rice area to the north. Lunama is a brackish backwater.

FIG. 1. Coastal lagoons of Sri Lanka. The location of the area shown in figure 2 is indicated at the bottom.

The Setting

Environmental Features

The mean annual temperature in this area is over 26C, and the average rainfall is often less than 1,200 mm. There are marked seasonal fluctuations in rainfall, and occasional droughts. Soils are chiefly reddish brown earths, but regosols, sandy soils, and silty clay alluvial soils also occur. Under these conditions of climate and soils, the land vegetation consists mainly of short, thorny scrub. There are fresh-water wetlands in river valleys, and the lagoons and their fringes have a distinctive swampy vegetation.

FIG. 2. The area of the Rekawa and Kalametiya-Lunama lagoon systems on the southern coast of Sri Lanka

FIG. 3. Rekawa lagoon

The area is accessible only by minor roads and tracks leading south from the coastal highway. Population density is low compared with the better-watered south-west lowlands. Settlements are widely scattered, and there are extensive areas of bare, unused land and thorny scrub. The chief occupations of the people living in the coastal region are agriculture, fishing, and the quarrying of shell grit. Chena (a type of slash-and-burn farming) and irrigated rice cultivation are the most important types of agriculture. With a few local exceptions the standard of living is low.

The infrastructure and service amenities of the area are poor. Flooding is extensive in the lowlands. Some villages do not have sealed roads from the highway, and tracks become submerged and impassable during the rainy season. Provision of clean drinking water is a major problem because in the dry season the local water supply is poor and adversely affected by high salinity. There are a few public water tanks provided by the government, but in general the water supply is inadequate. Another problem is lack of access to schools. Education is hampered by the fact that attendance is irregular, especially when flooding cuts off access.

FIG. 4. The Kalametiya-Lunama lagoon system


Studies of the vegetation in and around Rekawa, Kalametiya, and Lunama lagoons together with the associated fauna, especially fisheries, were carried out by S. S. de Silva and M. A. Pemadasa of Ruhuna University (Fernando 1986). Rekawa lagoon is bordered by a mangrove fringe dominated by Rhizophora mucronata and Bruguiera gymnorrhiza, narrowing toward the entrance from the sea. In Kalametiya lagoon, mangroves form a thin fringe around the eastern and southern shores, passing transitionally to a fresh-water fen vegetation. The mangroves on the eastern shore include Sonneratia casseolaris, backed by xerophytic vegetation. In Lunama lagoon, mangroves are confined to the southern shore and the channel linking it with Kalametiya Species include Excoecaria agallocha and Lumnitzera racemosa, backed by such xerophytes as Cissus quadrangularis and Cassia auriculata. In each of the lagoons the mangroves are a narrow, fringing community. In Rekawa and Lunama lagoons they persist by natural regeneration, but it is not yet clear whether they will survive in the freshened environment of Kalametiya lagoon, where fen and rush swamp may replace them.


There is local subsistence fishing in each of the lagoons, but only Rekawa has a commercial fishery. Both cast nets and kraals, built to trap prawns, are used for fishing. The kraals are temporary structures rebuilt each year, largely from bamboo and mangrove branches. They are used to trap two species of penaeid prawns, Penaeus indicus, which is the more abundant and productive, and Metapenaeus monoceros, which is present in smaller numbers and only for few months each year. In addition there is an incidental catch of fin fish in the kraals.

The prawn catch varies considerably with seasons and has also shown marked fluctuations from year to year. Variations are related partly to rainfall and runoff regimes and partly to tidal conditions. Biological studies have shown that the two species feed largely on molluscs within the lagoon and its mangrove fringe. Although it is probable that the prawn population is partly sustained by the ecosystem of which the mangroves are a part, this relationship has not been quantified.

Rekawa lagoon also sustains a fin-fish population, notably Mugil cephalus, Etroplus smatensis, Sarothesodan mossanticus, and a gobiid species. The fish population is not large but is sustained by the lagoon and its mangrove fringe as a nursery and feeding area.

As a result of the freshening of its water by the increase in runoff from irrigated fields to the north, Kalametiya lagoon is no longer important as a prawn area. It is possible that ecological changes resulting from freshening will permit invasion by fresh-water species. Rekawa lagoon also appears likely to be modified by the inflow of fresh water from a recently excavated canal.

Responses to Change

The Rekawa and Kalametiya-Lunama systems are subject to natural changes, related to fluctuations in such parameters as rainfall, runoff, and the extent of tidal ventilation as sea water flows in through an entrance of variable dimensions. In addition there have been changes due to human intervention, including the recent cutting of a canal to divert water from hinterland paddy fields into Rekawa lagoon, and the earlier, larger-scale diversion of fresh water into Kalametiya lagoon.

The United Nations University-Marga Institute project studied effects of such changes on the socioeconomic conditions of six village communities, three around the Kalametiya-Lunama lagoon system and three around Rekawa lagoon (Silva 1986). The significance of the mangrove-fringed system to the activities and livelihood of the local people was investigated in each community.

The three Kalametiya-Lunama communities were Thuduwa, Gurupokuna, and Kalametigoda:

Thudawa is a community of 74 households, 21 of which engage in local fishing. The total population is 425. The predominant caste in the village is Karawa, a fishing caste, but 11 households belong to other castes. All are Sinhala Buddhists except for one Christian household and two with Muslim men married to Sinhala women.

Gurupokuna has 60 households, of which 44 engage in sea fishing. The total population is 291. The population is entirely Buddhist, and all but one of the households belong to the Karawa caste.

Kalametigoda has 15 households, all of which engage in sea fishing. The total population is 76, all Sinhala Buddhists, and all but one of the households are of the Karawa caste.

The three Rekawa communities were Godigamuwa, Boraluwa, and Beliwala:

Godigamuwa has 111 households, of which 23 engage in lagoon fishing. All the inhabitants are Sinhala Buddhists and are of the Karawa caste.

Boralowa has 58 households, of which 19 engage in lagoon fishing. All the inhabitants are Sinhala Buddhists and belong to the Rajaka caste, whose traditional occupation is farming. Their involvement in fishing activities is relatively recent.

Beliwala is a community of 30 households, of which 22 engage in lagoon fishing. With one exception -a Muslim woman married to a Sinhala man - all are Sinhala Buddhists and are of the Karawa caste.

These communities should be considered coastal communities rather than lagoon communities, because their activities are not confined to the lagoons. Coastal communities can be distinguished from agrarian communities and fishing communities in the sense that these terms are normally used and understood. In both agrarian and fishing communities the life of the community has evolved around a major resource that provides its economic base. These coastal communities, on the other hand, depend on several resources in order to spread the economic risks associated with environmental fluctuations and to sustain their livelihood even at marginal subsistence levels. It may not be an exaggeration to say that uncertainty is the only thing these communities are certain of.

In all the communities land ownership is confined to ground that is too elevated for irrigation. The only agriculture suited to the existing climatic conditions in the absence of irrigation is a form of chena known locally as koratu, involving intensive cultivation of small cleared areas within the scrub. The extent of scrub jungle has dwindled because of increasing population pressure. By 1960 chena cultivation could be practiced in the area only with difficulty. A report on the resources of the area stated, "It is probably overpopulated for a dry zone area dependent on chena" (Canada-Ceylon 1960).

The question can then be asked why these coastal communities have not turned to the obviously accessible alternative resource of the sea for their livelihood. In fact participation in sea fishing has been very low in all these communities. The answer to this question leads to a general proposition which appears to be valid, at least in Sri Lanka. It has often been thought that the sea, unlike the land (which is largely held under private or state ownership! is an open resource available to anyone with the capacity and desire to engage in fishing. The reality is otherwise. Fishing communities jealously guard their respective beaches and fishing areas against intruders. The fishing communities are themselves largely closed communities with strong links based on caste and kinship. It is therefore not surprising that very few outsiders have entered the sea-fishing industry (Marga Quarterly Journal 1984).

There is also the further sociological fact that different communities perceive the status of sea fishers in different ways. The geographical location of Thuduwa is such that it is trapped between agricultural communities on the land side, while the lagoon blocks access to the sea. Sea fishing, particularly beach seine fishing and deep-sea fishing, have not been developed by this community as a source of income. Fishing rights in Gurupokuna and Kalametigoda are the sole prerogative of inhabitants of those communities and a few migrant fishermen. In social terms too there is an intracaste gradation between sea-fishing people and other types of fishing people that has made it difficult for the lagoon fishers to engage in sea fishing. Though of the same fishing caste, Thuduwa fishers concede that the sea fishers are "maha Marakkalas'' (big Marakkalas) while they are just Marakkalas. The emphasis is on ''maha," because the sea fishers deal in bigger varieties of fish, while other fishers deal in smaller fish for which there is a poor demand.

In Rekawa too, the non-participation of lagoon fishers in sea fishing is due to social constraints. Most respondents in Beliwala and Boraluwa stated they could work only as crew members, subordinate to the boat-owning sea fishermen, although they possessed the necessary skills to engage in sea fishing. The Godigamuwa kraal fishers attributed their non-participation in sea fishing to status differences in the occupations. The kraal fishers regarded themselves as superior to sea fishers on the grounds that, despite the higher incomes associated with sea fishing, the activity is concentrated within a few months of the year and for the rest of the year the sea fishers have little to systain them. They regarded the kraal as an asset yielding a more stable income throughout the year.

At present the pattern of employment is such that there is a great emphasis on fishing as a source of income. For Thudawa and the three Rekawa communities the most important source is lagoon fishery. All respondents in Rekawa engaged in fishing in the lagoon during the prawn season, which lasts for four moths, beginning in December and reaching its peak in January. In Kalametiya there was no clearly delineated prawn season, and the prawns caught were of a commercially less valuable variety.

The price paid to the producer of commercially salable prawns is in the range of 67.50-79.50 Sri Lankan rupees per kilogram, while the poorer variety is in less demand and is priced around Rs 27 per kilogram. The highest average monthly incomes are recorded in the prawn season. In Boraluwa and Beliwala most of the annual income of fishing households is realized during the prawn season. Lagoon fish account for most of the income of Godigamuwa households. Income from fishing in inland reservoirs accounts for most of the income of Thuduwa households. In all four communities the number of household members engaged in employment other than fishing is low.

Daily wages for agricultural labour are Rs. 15-25 for males and Rs 15 for females (much less than the price of a single kilogram of prawns). During land preparation and harvesting seasons these wages may rise to Rs 30 and Rs 25 for males and females respectively. Labour is grouped into two broad categories: agriculture-related work and fishing. Agriculturerelated work in Rekawa means work in irrigated fields in the region outside these villages. Some people commute to these fields daily during the periods when labour is required. They also may obtain wages for labour in coconut estates further in the interior. This type of work is not available regularly throughout the year. In Boraluwa, the figure for those engaged in agricultural work is higher (83 per cent). The predominant work is koratu, the intensive cultivation of small plots, often of less than half a hectare. Since land for cultivation is scarce in the village, those who engage in this type of cultivation rent from landowners in the hinterland.

Even though at present lagoon fishery accounts for a considerable part of the income of the Rekawa communities, in the long term their dependence on lagoon fishing is likely to be only a temporary phase, as other resources become accessible. For Thuduwa the phase of great dependence on lagoon fishing is over, because Kalametiya lagoon has undergone several changes beyond the control of the local inhabitants and its fish resources have been severely depleted. At Rekawa the lagoon fishery resources may also undergo changes due to factors beyond the control of the people, forcing the Rekawa communities to increase their dependence on other sources of income such as agricultural labour.

Fluctuations in the degree of dependence are not confined to the lagoon resources, as can be seen in the Kalametiya communities. Until the 1950s the lagoon played only a marginal role in economic activities of the community. At that time the three communities of Thuduwa, Kalametigoda, and Gurupokuna had semi-subsistence economies based on shifting cultivation. Agriculture rather than fishing was the main source of livelihood. The vast tracts of scrub that surrounded the villages provided ample land for cultivation. Lagoon products had a very limited market, mostly confined to the agricultural communities of the coastal region.

Cultivation could not continue as the main source of livelihood, however, because a growing population began to claim increasingly large tracts of farmland for settlement. Rapid population growth in these areas was associated with welfare measures implemented by successive governments, the more important among which were the anti-malaria campaign, better healthcare services, improved transport, and governmentsubsidized food. As mentioned, a report on the resources of the Walawe-Ganga basin in 1960 concluded that the area was probably over-populated for a dry zone dependent on chena.

The net outcome of these processes was that peasants, most of whose income had until then been derived from farming, were forced to increase their use of alternative resources, which previously had played only a marginal role. One such alternative was sea fishery, the exploitation of which had up to then been in the hands of outsiders with access to capital and technology in the form of craft, gear, and skills.

Lack of capital was a definite constraint that hampered the local inhabitants from taking on large-scale sea fishing. At this point a coincidence of government policies geared to develop and modernize the seafishing sector acted in the favour of Gurupokuna and Kalametigoda. A principal feature of the government policies was that "in selecting the beneficiaries, government chose workers who were not owners of the traditional boats themselves. The decision had major consequences for the social hierarchy and the structure of power as it had evolved through the traditional fishing based as it was on the traditional technology" (de Silva 1 977).

Although the processes outlined above worked to the advantage of the Kalametigoda and Gurupokuna communities, they had the opposite effect on the Thuduwa community. Thuduwa's disadvantageous geographical location made access to beach-seine sites and harbour facilities difficult. The gradual acquisition of use rights brought about the development of marine fishing in Gurupokuna and Kalametigoda. The restrictive regulations on the clearing of scrub for chena cultivation reduced Thuduwa to dependence on two highly seasonal sources of income: lagoon fishing and farm labour. The lagoon fishery proved to be short-lived, being the victim of unintended consequences of a national agricultural policy. The construction of the Walawe Right Bank Scheme and its system of reservoirs and irrigation channels resulted in a large volume of residual fresh water from the newly opened irrigated lands draining into Kalametiya lagoon. Although a canal has been built at the marine entrance to allow water to escape to the sea, the continuous flow of this water requires frequent clearing of the sand bar to prevent inundation of paddy fields located in the upper reaches of the lagoon.

As a result of these changes, the communities of Gurupokuna and Kalametigoda have merged and enjoyed a moderate prosperity through development of marine fisheries, whereas Thuduwa remains less economically developed.

At present 66 per cent of the fishers in Thuduwa derive their income from inland fisheries, but access to this source is becoming increasingly difficult because local communities around the inland reservoirs have organized themselves into "fresh-water fisheries extension societies," one of whose major aims is to limit the fishing rights in these reservoirs to their membership.

Today the communities in Rekawa are confronted with a common issue, the threat of the loss of the lagoon fishery, which is their most important source of income. Construction of a canal into the lagoon to drain an adjacent paddy tract of about 37 hectares, known as Thangalu Welyaya, has already caused changes in the lagoon ecology. These may explain the very low prawn catches during the past season. The communities that depend on the lagoon have complained bitterly about the new canal, but, given the costs of canal construction, its closure is an extremely remote possibility. The fishing community is not politically strong enough to overrule the agricultural community.

Data for Kalametiya and Rekawa lagoons show that open access to fishery resources cannot be maintained while the resources are economically viable. Rekawa lagoon has never been an "open-access" resource. The Godigamuwa community in Rekawa has monopolized the best sites for kraaiing for several generations. Prior to the 1970s, when the demand for lagoon fish and prawns was low, access to the lagoon outside the kraaling area was open to local inhabitants who used cast nets for fishing. The cast net posed no threat to the kraal fishermen, whose technology was comparatively superior. With the increase in population and the nonavailability of other sources of income, net fishing has increased steadily.

In the latter half of the 1970s, with the development of the tourist industry and the export market for prawns, demand resulted in prices for prawns rising even higher than for bigger sea fish. With the new marketing conditions, the traditional monopoly of the kraal fishermen has been challenged in an indirect way through use of a more efficient mode of fishing, the drift net. Prior to the late 1 970s drift nets were used to some extent, but only to catch fin fish, and the minimum legal mesh size of the nets was 4.2 cm. The increased demand has attracted a large number of fishers to the profitable prawn industry. Almost all of them use illegal nets with a mesh size of about 2.5 cm. Disputes between krall fishers and drift-net fishers have resulted in tighter government regulations. The number of kraals, their specifications, the number of drift nets and their mesh sizes, the numbers of fishers entitled to operate kraals and drift nets are all regulated, but enforcement of the regulations has been ineffective and has not reduced the scramble for a greater share of the fishery.

In Kalametiya the reverse process has occurred. Though the lagoon fishery in Kalametiya lagoon has been virtually destroyed, a fisheries extension society has been established to limit exploitation of what is left of the resource to a group of Thuduwa fishermen. Extension societies have been established in inland fishing communities also, and fishing rights on the reservoirs are now the prerogative of the members of these societies. The absence of any tenurial arrangements in Kalametiya lagoon has made it difficult to enforce the limitation of fishing rights to members of the society.

New market conditions for prawns and lobsters during the latter half of the 1970s revealed gaps in the traditional tenurial system, on which the inhabitants of these coastal communities have been quick to capitalize. One such new opening is lobster fishing. The traditional sea tenure system revolved around beach-seine, off-shore, and deep-sea fishing. Lobster fishing is treated separately because it does not require a particular site. All that is necessary is gear and some means of navigation in the shallow sea. Most fishers use either dugouts or inflated motor-vehicle tyre tubes for the purpose.


One important implication of this study for policy-planners is that undesirable consequences can follow from a lack of understanding of the ecological and socio-economic unit for planning integrated development. An overall development plan embracing a whole region and taking into account diverse interrelated factors is needed to avoid uneven or skewed development, achieved at the expense of certain sections of the population.

This study also highlights the need for development planners to recognize interacting ecological and socio-economic factors involved in the implementation of a development project. The absence of such perceptive planning is seen in the way in which the lagoon resources of the coastal communities of Rekawa have been adversely affected by the irrigation outflow canal for the development of the Thangalu Welyaya tract, which was built despite the fact that the probability of a harmful ecological change was obvious from a glance at Kalametiya lagoon.

Throughout this study it has been evident that the mangrove fringes of these lagoons have not been of major interest or importance to the coastal people, even though they may play a significant role in the lagoon ecosystems. Mangroves do not form extensive landscapes or habitats for human occupation in Sri Lanka. They are but one aspect of a diverse environment, exploited in many ways by the economically marginal communities living in this coastal region.


Canada-Ceylon. 1960. Report on reconnaissance survey of the resources of the Walawa Ganga Basin. Canada-Ceylon Colombo Plan Project, pp. 107-109. Government Press, Colombo.

de Silva, M. W. A. 1977. "Structural change in a coastal fishing community in southern Sri Lanka." Marga Quarterly Journal, 4: 47-86.

Fernando, S., ed. 1985. "Selected lagoon systems in the Hambantota District of southern Sri Lanka." Unpublished report. Marga Institute, Colombo.
- 1986. "Use and management of coastal lagoons in southern Sri Lanka," Marga Quarterly Journal. In press.

Marga Quarterly Journal. 1984. "Fishery." Special issue. Vol. 7, nos. 2 and 3.

Panayotou, T. 1984. "A resource sector with a difference: Competitive marketing in Sri Lankan fisheries." Marga Quarterly Journal, 7: 15 - 28.

Silva, A. 1986. "Socio-economic aspects of coastal lagoon communities in southern Sri Lanka." Marga Quarterly Journal. In press.

Sivakumar, J. 1980. "Evolution of coastal sand and vegetation resources of the north-eastern coastal belt of Sri Lanka." In J. I. Furtado, ea., Tropical ecology and development, pp. 109-117. International Society of Tropical Ecology, Kuala Lumpur.

Contents - Previous - Next