A Assessing productivity of free breeding fish …A Assessing productivity of free breeding fish...
Transcript of A Assessing productivity of free breeding fish …A Assessing productivity of free breeding fish...
A
Assessing productivity of free breeding fish species
in farmer-managed irrigation tanks in the
Dry Zone, Sri Lanka
by Carlos Yanes-Roca
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Acknowledgments
I would like to thank too many people for their help during my thesis:
Dr. Dave Little for giving the chance to work in this project and the patience of going
through all my grammatical mistakes.
Francis Murray for his help and support in Sri Lanka
All the assistant researches and house mates, for helping with the translations and other
things… (Susantha, Prythanta, Bandara, Tharaka, Deeptha and Yasantha)
To Rasak, for looking after me during the lonely weekend and for his magnificent lime
sodas.
To Dr. Sarah for his academic help.
The volleyball team of Galgamuwa great distraction after hard day of work.
To Astrid Holzer for her moral support during my days in Sri Lanka.
Of course my family for their unconditional support.
And finally to my computer for not crashing in Sri Lanka.
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Abstract
. Man made reservoirs (tanks) in Sri Lanka are found throughout the country representing
nearly all the country’s surface water (2% of the total land surface), but are particularly
important in the Dry Zone. The current study was carried out to assess if tanks have
potential as a central element in the development of aquaculture.
The analysis of seasonality, water catchment, location and water input were the main
factors used to classify the potential of various types of tank for fish culture. These
factors, together with the analysis of peoples livelihood’s around the tanks and the impact
of macrophytes on tank productivity, has led to the conclusion that seasonal tanks (e.i.
those that dry out completely) have the potential for development of a sustainable
aquaculture.
In an analysis of the priorities of water usage, fisheries was found to be lower than
irrigation and bathing and potential conflicts were identified that constraint development
of fish culture in Dry Zone tanks. Other constraints such as macrophyte infestation do not
represent a ma jor impediment since the infestation occurs less severely in seasonal tanks
where the main species are relatively easy to remove.
The development of fish culture in the Dry Zone may improve the poor nutrition of
people living there that are particularly dependent on freshwater fish, but a holistic
approach to understanding constraints and peoples’ priorities will be essential to
increasing fish yields on a sustainable basis.
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Table of Contents
Acknowledgements Abstract
1 Introduction………………………………………………………………………1-28
1.1 Geography
1.2 Climate
1.3 Vegetation and fauna
1.4 Social-economic Aspects
1.5 Inland water resources
1.6 Agriculture
1.7 Fisheries
1.8 Macrophytes
1.9 Objectives
2 Methods………………………………………………………………………….29-32
2.1 Data collection
2.2 Data Organisation structure
2.3 Data analysis
3 Results……………………………………………………………………………..33-49
3.1 Tank Classification
3.2 Natural Fisheries productivity
3.3 Macrophytes
3.4 Poverty
4 Discussion…………………………………………………………………… ….50-54
References……………………………………………………………………………55-57
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Appendix
1.Average rainfall and temperature
2. Monsoon rainfall
3. Sri Lanka surface water
4. Sri Lanka’s population density distribution
5. Data clearing methodology
6. Macrophytes taxonomic identification
7. Data clearing disc* (attached to the back)
8. Statistical Analysis Result tables
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List of figures
Figure 1. Study area and it’s geographical location (Murray 1999)…………… ………1
Figure 2. Distribution of small-scale irrigation systems in Sri Lanka ……………………6
Figure 3. Cascade system diagram (Source: Sakthivadivel 1996)……………… ……...8
Figure 4. Paddy fields…………………………………………………………… ……...9
Figure 5. Tank cover with aquatic plants…………………………………………… ….20
Figure 6. Nymphacea Lotus……………………………………………………………..21
Figure 7. Total tank distribution (%), from each tank type, in terms of seasonality
Patterns……………………………………………………………………….30
Figure 8. Seasonality and maximum water spread relationship. ………………………..31
Figure 9. Average fisheries annual production from two types of fishing: collective
fishing and pre-collective fishing at the different tanks………………………………….32
Figure 10. Collective fishing main caught species and it distribution at the different
tanks……………………………………………………………………………………...34
Figure 11. Tank cover with salvinia sp………………………………………… ……..35
Figure 12. Tank cover with Nelumbo nucifera…………………………………………..35
Figure 13. Utricularia vulgaris ………………………………………………………….35
Figure 14. Nymphacea Lotus…………………………………………………………….35
Figure 15. Mean percentage of area covered by different macrophytes within the 92
tanks…………………………………………………………………………… ………36
Figure 16. Macrophytes encroachment in tanks by type , from 92 tanks……………….37
Figure 17. Aquatic encroachment and fisheries productivity correlation from collective
fishing production………………………………………………………………………..40
Figure 18. . Aquatic encroachment and fisheries productivity correlation from pre-
collective fishing production……………………………………………………………..40
Figure 19. Effects of desilting over the macrophytes encroachment. Represent the total
number of tanks (%), by degree of rehabilitation receive if any and the percentage of tank
area covered by macrophytes…………………………………………………………….42
Figure 20. Average distance to main infrastructures from the villages allocated at the
different tanks……………………………………………………………………………44
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Figure 21. Distribution of land ownership opposed to paddy cultivators owners within the
different tanks……………………………………………………………………………47
Figure 22. Temporal labour (coolie) distribution at the different tanks…………………48
Figure 23. Distribution of type of houses at the different tanks. Total percentage and total
number of houses………………………………………………………… ……………49
Figure 24. Caste distribution at the different tanks……………………………… ……..50
Figure 25. Salvinia molesta physiology…………………………………..Appendix
Figure 26. Salvinia molesta in the wild …………………………………..Appendix
Figure 27. Pistia stratiotes ……………………………………………….Appendix
Figure 28. Echhornia crassipes photo ……………………………………Appendix
Figure 29. Echhornia crassipes drawing ………………………………….Appendix
Figure 30. Nelumbo nucifera flower ………………………………………Appendix
Figure 31. Nelumbo nucifera at the tank …………………………………..Appendix
Figure 32. Ceratophyllum demersum ………………………………………Appendix
Figure 33. Ceratophyllum demersum leaves ……………………………….Appendix
Figure 34. Eleocharis dulcis ………………………………………………..Appendix
Figure 35. Nymphoides indica photo ……………………………………….Appendix
Figure 36. Nymphoides indica drawing ……………………………………..Appendix
Figure 37. Utricularia vulgaris at the tank ………………………………….Appendix
Figure 38. Utricularia vulgaris physiology …………………………………Appendix
List of tables
Table 1. Land utilization within agricultural holdings…………………… ……………11
Table 2. Annual Aquaculture production…………………………………… …………15
Table 3. Tank Classification based on water seasonality……………………………….28
Table 4. List of Aquatic plants found in the field and their common names… ………38
Table 5. Uses, introduction agent and control methods from the main macrophytes in 20
tanks……………………………………………………………………………………...41
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1. Introduction 1.1 Geography
The study has been carried out in Sri Lanka, a teardrop shape island in the Indian
Ocean. With 353 km long from North to South and 183 Km at its widest, has an area
of 66,000square Km, comparable to the size of Ireland or Tasmania (Niven et al;
1999)
Sri Lankas topography is characterised by a south central mountain range, which
reaches heights of 2524m above the sea levels (Piduratagala) and known as the Hill
country, surrounded by a coastal plain.
The island is characterised by a variety of landforms, ranging from flat erosion or
ridges, plateaux, and valleys. Sri Lanka is considered to be made up of seven major
land formed units, a coastal plain, a continental shelf, a circum-island peneplain, a
central massif, the Sabaragamuwa hills, the Gayola hills and the Elahera ridges (De
Silva, 1988).
The flat North-Central and northern
plain extends from the hill country all
the way to the northern tip of the
island, region where the study was
based, Puttalam and Kurunegala
Districts, NorthWest Province within
Dry Zone.
(Figure 1)
1.2 Climate
The island climate is tropical humid,
although a range of climatic patterns
are found on the island.
Temperature and precipitation are the
most important climatic factors of the Figure 1 . Study area and it’s geographical location (Murray 1999)
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island (Appendix 1). In the same token the most dominant factor determining the
climatic patterns are the two monsoons, the south-west active from June through
September and the north-east active from December to February, and the related
inter-monsoonal effects (De Silva, 1988).
Due to its geographical location with respect to the central mountain rage (Hill
country), which acts as a physical barrier, the North West Province is barely affected
by both monsoons, therefore the annual mean rainfall (1270-1905mm) is considerably
lower than at the central, west, and southern parts of the island (2540-5080mm) (De
Silva, 1988).
The two main rainy seasons, directly related to the already mentioned monsoons are
the Maha season from October to March and the Yala season from April to June. The
Maha season is the most important season in terms of rainfall compare to the Yala
(Appendix 2).
From June to September the third season, or Dry season, dominates the area, in which
literally no rain falls.
1.3 Vegetation and Fauna
1.3.1. Vegetation
Of the biotic resources of Sri Lanka, the vegetation is the most outstanding in view of
its diversity, species-richness, high degree of endemism and its great economic
potential (Pemadasa, 1984).
Nearly 30% of the 3000 species of vascular plants in the island are estimated to be
exotic. Five major types of communities exist:
a) Marine vegetation. Consisting of salt marsh vegetation, mangrove vegetation,
sandy shore vegetation, sand dune vegetation (along the coast)
b) Fresh water aquatics and marsh communities.
c) Tropical wet evergreen forests.
d) Tropical semi-green forests.
e) Tropical thorn forest found in the north-western and south-western coastal
areas.(Abeywickrema, 1955)
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1.3.2 Vegetation of the Dry zone The overall picture of the vegetation in the Arboretum reflects the physiognomy of a
Dry Zone forest. But given its regeneration from the previously degraded scrub
jungle, this forest is one of second growth or a secondary forest.
The distribution of the different vegetation types in this forest Arboretum is
controlled chiefly by the conditions of its bioclimate. IN spite of the restricted extent
of the Arboretum, these vegetation types may be broadly distinguished as follows:
a) Tropical dry (mixed) evergreen forest.
b) Moist tropical semi-evergreen forest.
c) Scrub jungle (Cramer, 1993).
1.3.3. Fauna
The fauna of Sri Lanka is of the most unusual and varied anywhere. Eighty six
mammal species include elephants, many species of deer, monkeys, leopards, sloth
bears, loris, porcupines, jackals, dungons, otters, etc.
Over 400 hundred bird species inhabit the island, of which 21 are endemic (Niven et
al, 1999).
In terms of fish fauna, Sri Lanka has a wide variety of marine tropical fish species
and freshwater inland fish species.
Between 51-55 freshwater indigenous fish species inhabit inland water bodies.
Twelve of these species are listed as food fish species (Fernando & Indrasena, 1969)
Since the first introduction of Salmo trutta in 1898, a further 19 species of true
exotics and two estuarine transplants have been added to the inland fish fauna. These
introduc tions do not include pet-fish or aquarium species. Until now no significant
detrimental effects caused by the introductions have been observed, either to the
indigenous fish fauna or the aquatic flora and other fauna. On the other hand, Sri
Lanka stands out as a classic example of a proven success of exotic finfish species,
i.e. Oreochromis mossambicus. Other introductions include: Cyprinus Carpio,
Oreochromis niloticus, Tilapia rendali, Tilapia zillii, etc. (De Silva, 1988)
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1.4 Social-Economic Aspects
14.1 Population
The population of Sri Lanka is estimated to be 19 million ( De Silva, 1997). This
implies an average density of 278 persons per Km², which is 21st highest in the world
(Perera, and De Silva, 1997).
As in any country, the distribution is very uneven. Population is clustered extremely
densely in a few areas in the south-western and central parts of the country and spread
out much less densely in most of other parts, particularly south-eastern and northern
parts, south of the Jaffna peninsula (Appendix 4)
While the absolute size of population has been increasing, the rate of growth has been
declining. Sri Lanka’s population growth, which was as high as 3% in 1950s, has
gradually dipped close to 1.3% in the1990s (Perera and De Silva, 1997).
Population projections shows a slow increase of population, at least till the third
decade of this century to reach the 21-23 millions, to thereafter, it may remain
roughly at that level (De Silva, 1997).
1.4.2. Economy and Markets
From early historical times, Sri Lanka, was world renowned for its rich spices. The
importance of spices in the export agriculture sector diminished with the
establishment of large-scale plantations, initially of coffee followed by tea, rubber
and coconut (Figure 4). Another plant which has a key importance in the island’s
economy in the sugar.
In terms of the industrial infrastructure, Sri Lanka has a Gross Domestic Product of
26% with agriculture accounting for 24% and 50% services.
Four are the main components of the industrial sector: manufacturing, mining and
quarrying, construction and utility services, account for 15.2%, 7.8%, 2% and 1.5%
respectively (Perera and De Silva, 1997). The textile and garment sectors account
for the highest contribution in terms of output employment. Food, beverages and
tobacco processing representing 24% of output while 18% of the output is accounted
for chemicals, petroleum, plastics and other rubber products (Perera and De Silva,
1997)
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Development of plantation agriculture and the gradual transformation of subsistence
farming to commercial farming could be considered as factors that contributed to the
expansion of internal trade in the country. The expansion of the plantation industry
necessitated the supply of its requirements; food items for workforce, tools and
implements and textiles. Most of these items had to be imported and distributed
through a network of wholesalers and retailers (Perera and De Silva, 1997)
1.4.3 Religions
Sri Lanka has a wide variety in terms of ethnic and religious groups. Although the
following information is based on the 1981 census, the distribution is still quite
representative of the actual distribution.
The main or bigger ethnic group at a 74% is the Sinhala, followed by the Sri Lanka
Tamil with 12.7% of the total population. Indian Tamils (5.5%) and Moors (7%) are
then third and forth ethnic groups.
In terms of religious groups, there is a Buddhist majority, which represent the 69.3%
of the population, followed by Hindu with 15.4% of the total population. Muslim and
Christian groups represent 7.6% each from the total (Perera and De Silva, 1997)
1.5 Inland Water Resources
In view of the topography of the island and the overall rainfall pattern, a substantial
water resource is to be expected. The natural water resources of the island take the
form of extensive river and stream systems, and the associated flood plains and
marshes. Sri Lanka does not have any natural lakes (De Silva, 1988).
1.5.1 Irrigation System
Natural reservoirs in Sri Lanka are characterized by its little abundance, although it
has 3 ha of inland water per Km² of land (almost 2% of the land surface- De Silva,
1998) [Appendix 3]. Most of this water area is a man-made legacy of ancient
irrigation systems. The purpose and determination in the construction of the irrigation
systems are depicted by the words of Parakrama Bahu the Great (1153-1186 AD):
“Let not even a drop of rain water go to the sea without benefiting the man”. In
consequence a series of watershed systems dominated the landscape, especially in the
Dry Zone.
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Irrigation developed hand-in-hand with rice growing; rice was, and is, the staple
food. Today Sri Lanka has more than 17,000 functioning irrigation schemes
covering approximately 500,000 hectares. About 99 percent of these schemes
irrigate less than 80 hectares each and are classed as “minor” irrigation schemes. In
total, minor schemes irrigate about 150000 hectares.
Figure 2. Distribution of small-scale irrigation systems in Sri Lanka
1.5.2 Cascade Systems
A cascade system, in this case tank cascade, or a chain of tanks, is a series of small
reservoirs that are constructed at successive locations down one single common
watercourse. Thus any excess water flowing from one tank in such a chain is captured in
the next, downstream tank (Itakura et al; 1992).
Spill events, water drainage, canalisation or rainfall, are the main water sources by which
the tanks (Figure 3) progressively fill. This system has key characteristic the direct
interrelationship between all the tanks on the watershed. Therefore any disruption
occurring at any tank will affect directly or indirectly the other tanks specially those
below (Figure 3).
Due to its characteristics, this system has a high potentiality as a water system:
(Source: Cook, 1931 in Murray, 1999)
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1) Function of re-storing and re-using drainage return-flow or recycle within the
system;
2) Buffer function, alleviating the imbalance between water demand in the command
area and the water supply from the tank, which occurs owing to the fluctuation of
both field water requirement and rainfall-runoff discharge (Itakura et al 1991).
1.5.3 Tanks
Tanks are created by the construction of earthen dams across seasonal streams (Figure 4).
Maximum water spread rages from 4-50ha, whilst 80% are 25ha or less, whilst the
average village tank is estimated to have an irrigable area of 42ha (Land Commissions
Report 1985, Murray 1999 a). Rainfall, although relatively high (>1000mm/year), is
highly variable and soils are generally shallow and porous. Many tanks only fill in above
average rainfall years. They receive most water during the main monsoon (Maha, Oct-
Jan) and irrigate some 20-30ha during the subsequent main cultivation (Maha, Oct-
March). Water levels recede gradually from Feb-Mar onwards, but may fluctuate due to
intermittent rains during the second monsoon (Yala, Apr-Jun), evaporation and
occasional draw down for agricultural purposes during the second cultivation period
(Murray, 1999 a).
An estimated 18000 tanks are clustered into 3500 to 4000 small tank cascade systems
(STC’s) with the greatest concentrations in areas of the Northwest and North Central
Provinces (DAS 1996). Over half of these tanks are operational, of which 80% are 25 ha
or less at maximal waterspread. All but the smallest, effectively private tanks, (<5ha) are
under state jurisdiction but community manage on a daily basis. Tanks are arranged
within cascading sequences of between 2-25 tanks. Tanks tends to decrease in size and
increase in seasonality with progressive movement towards the top of the watershed
(Murray, 1999)
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Figure 3. Cascade system diagram (Source: Sakthivadivel, 1996 in Murray, 1999 a).
1.5.4 Tanks and Seasonality
Water level in tanks in the Dry zone are highly variable throughout the year. These
fluctuations define four main types of tanks: Perennial, semi-seasonal, seasonal and
highly seasonal:
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Perennial tanks : have not dried out in living memory.
Semi-seasonal: dry one or two times every five years.
Seasonal: dry two to three time every five years.
Highly seasonal: dry every year.
1.5.5 Paddy fields
Paddy, a word of Malaysian origin, is used for both the unhusked grain of rice as well as
the leveled plot of wetland enclosed by earth bunds for the cultivation of semi aquatic
grass Oryza sativa.
Immediately below almost every tank, this principal irrigated crop, paddy is found
(Figure 4). In total, paddy is grown on nearly 600.000 ha of land. Nearly half of this total
is grown under minor and medium irrigation sys tems. Of the remaining 250,000ha under
major irrigation (>600ha) nearly 130,000ha are under the Mahaweli Development
scheme1. Straddling North Central Province is the Mahaweli H irrigation system, part of
the Mahaweli development program initiated in 1975 to relieve population pressure in the
Dry Zone to the west, which is the main location where the research was carried out
(Murray, 1999).
Figure 4. Paddy fields at the Dry Zone. Sri Lanka
1.5.6 Water Quality
Surface waters draining from the granite hills of Sri Lanka is normally clear, soft and
more or less neutral in pH. Lowland standing bodies have a higher level of dissolved
1 Largest multipurpose national development programme. Main objectives are: generation of Hydropower, settlement of landless and employed families and provision of irrigation facilities for the Dry Zone.
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solids, conductivity and are generally alkaline. pH values varies widely, depending on the
season. Generally pH levels fell within 6-8.5, although higher values occur in the lower
tanks (Murray, 1999).
Water temperatures in tanks are highly stratified, ruled by daily and seasonal patterns.
Temperature reach 35º C in shallow paddy fields and shallow receding waters of smaller
ponds (Murray, 1999). Mean water temperatures are around 25º C.
Turbidity, characterized by high silt levels, occurs especially after heavy rains and in
smaller upper watershed tanks. Widespread encroachment of aquatic macrophytes and
degradation of the catchment areas is likely to have increased silt levels whilst causing a
net reduction and increase in the organic and inorganic nutrient load of water flowing to
lower tanks in the longer term (Murray, 1999).
High levels of pesticides are mainly used in irrigated areas. The presence of such
chemicals vary with the season, position in the cascade system and cultivation strategies.
Therefore during the dry season and at lower tanks the accumulation of pesticides is
greater. (Murray, 1999)
Most of the water quality parameters are within acceptable ranges, although water quality
decreases during the dry season.
1.6 Agriculture
Agriculture continues to be the mainstay of the national economy though it’s distribution
to GDP is in decline as the manufacturing sector expands (it’s share rising from 14.8% in
1985 to 197% in 1994- Central Bank 1998). Prior to 1997, farmers benefited from
assured markets and high production subsidies under a centrally planned economy, which
stressed self-sufficiency in food production (Weragoda 1998, in Perera et al 1997) but
stifled economic growth. These benefits along with projectionist exchange controls and
import quota restrictions were gradually abolished during two decades of progressive
economic reform, which aimed to encourage greater market orientation and production
efficiency amongst producers (Kodithuwaku 1997 in Perera et al 1997) and export
orientated economic growth (Kelegama 1999).
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1.6.1 Agricultural land use
In the rainfed focus areas of this project, most villagers derive their primary source of
household income from farming activities. Paddy (the staple food along with fish) is the
principal irrigated crop. Dryland crops are grown under a traditional pattern of shifting
‘slash and burn’ or fixed highland cultivation, whilst vegetables and other cash crops are
also grown in smaller home-gardens. Livestock holding, already low within this
predominantly Buddhist society, are declining further due to reduced pasture availability
and mechanization of tasks formerly undertaken by draught animals (Central Bank 1998
and pers. Obs. in Perera et al 1997)
Table 1. Land utilization within agricultural holdings in Sri Lanka
(Source: Garmage, 1997, ESCAP 1997)
Type of agricultural land use Area Total (ha) Percentage
Total land area 6.5 Natural forest cover 1.5 Total area under agricultural production 3.2 100 A. Permanent cultivation 2.07 65.8 Plantation (tea, rubber, coconut) 0.94 29.4 Mixed upland crops and home-gardens 0.6 18.8 Total irrigated Land 0.6 18.8 Irrigated paddy under seasonal tanks (<80 ha) 0.23 7.4 Irrigated paddy under seasonal tanks (80-600 ha) 0.05 1.6 Irrigated paddy under major irrigation (>600 ha) 0.25 7.8 B. Shifting slash and burn 0.95 29.7
C. Pasture 0.02 0.63 D. Uncultivated cultivated area 0.092 2.9
1.7 Fisheries
The fisheries sector plays a vital role, contributing as much as 65% of the animal protein
to the Sri Lankan diet. Although the contribution of the fisheries to the Gross National
Production of the country is lower than that of the agriculture sector, fisheries play an
important role in the nutrition and socio-economics of the country. The local demand for
fish and fishery products has kept rising progressively each year, with the demand in
1998 (319.881 tons) being 3,1% more than the demand in 1997 (NARA, 2000, 1999)
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The inland capture fishery of Sri Lanka is a lucrative commercial enterprise based on two
African cichlids, Oreochromis mossabicus and Oreochromis niloticus establish in large
perennial reservoirs of the Dry Zone (Nathaniel, 2000).
Although the marine sector dominates fish production in Sri Lanka, in rural areas, where
poverty and malnutrition prevail, the demand is for cheaper locally available freshwater
fish. The rural community in inland dry zone areas is dependent on freshwater fish for
81% of its protein requirement (Nathaniel, 2000).
Due to the lack of protein, 62% of mothers and 66% of children in rural areas suffer from
malnutrition and other diseases. On the other hand, due to the lack of food in their home
38% of children going to school in rural fishing communities do not attend to school
(Nathaniel, 2000, 1999)
1.7.1 The capture fishery
Of the 18 food fis h species introduced, the Java or Mossambique tilapia Oreochromis
mossambicus has been a resounding success, while two other cichlid species
Oreochromis niloticus and Tilapia rendalli, have established breeding populations. Two
air breathing specie, the snakeskin gourami (Trichogaster pectoralis) and the giant
gourami (Osphoronemus gourami) have establish highly localised populations, that are
high enough to support a fishery on the western coastal flood plains (Penthiyagoda,
1999).
Several non-tropical major carp species have also been introduced such as the common
carp (Cyprinus carpio), Indian carp (Catla catla, Cirrhinus mrigala and Labeo rohita)
and Chinese carp (Aristichthys nobilis, Ctenopharyngo donidella and
Hypophythalmichthys molitrix). Of these species only the common carp (Cyprinus
carpio), and rohu (Labeo rohita) have established self-sustaining populations in Sri
Lanka (Penthiyagoda, 1999). The common carp now occurs in many headwater streams
above elevations of 1500 m (Penthiyagoda, 1999). Most of the remaining species
introduced as food fish persists in small populations, which may die out in the near
future.
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1.7.2 Indigenous fish fauna
The most abundant indigenous species in Sri Lankan reservoirs are the minor cyprinids
(<10 cm) such as Amblypharyngon melottinus, Puntius filamentosus, Puntious chola and
Puntius dorsalis, which form a substantial resource (De Silva and Sirisena, 1987;
Amarasinghe, 1994; Pet and Piet, 1993; Piet 1996).
Although these fish could gainfully be exploited without harming the existing
commercial fishery, large-scale commercial exploitation is unlikely to occur under the
existing fishery regulations, which prohibits the use of small meshed nets. However,
small quantities of these small cyprinids could also be used for the preparation of
fishmeal or dry fish production (De Silva, 1996; Amarasinghe, 1990)
Of the larger indigenous species food fish, the striped snakehead (Channa striatus ) and
eels are among the high value species. Two indigenous cyprinids P. sarana and L.
dussmeiri along with the estuarine transplant Etroplus suratensis, which has established
itself in some reservoirs presently contribute to a small-scale commercial fishery. Two
silurids, Ompok bimaculatus and Wallango attu were major constituents of the inland
fishery prior to the introduction of exotics.
Reservoirs are not suitable breeding grounds for indigenous species, since these fish
require riverine habitats for spawning (De Silva, 1983).
1.7.3 Fisheries of perennial and seasonal tanks
Stocking trials in rain-fed village tanks have demonstrated yield potential in excess of
800 Kg/ha/yr-¹ (Chakrabarty, 1983 in Murray et al 2000), though results have been
highly variable and so far no sustained adoption has been achieved. In the absence of
stocking initiatives, substantial though erratic natural production occurs in such tanks
(Murray et al, 2000)
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Production levels2 during seasonal collective fishing are between 150-200 kg/ha for tanks
holding water for less than 6 months. Greatest variation exists in the production levels
from medium sized semi-seasonal tanks (drying intermittently), where the potential for
natural repopulation depends on seasonal hydrological linkages between tanks at the
wider cascade level. Such linkages are in turn determined by a number of factors,
principally seasonal rainfall patterns and tank rehabilitation practices. Village patterns
and tank production, which are concentrated mostly during the dry season, remain
invisible to official statistics, being used almost exclusively for local household
consumption (Murray et al, 2000).
1.7.4 Fisheries Management 3
Fish production in small tank systems appears to be of greater importance to the
livelihoods of villagers in the lowest wealth rank relative to those in the middle and upper
ranks. This is attributed to several factors. Most of the fish consumed in cascade systems
originates from large perennial reservoirs, yielding a cheap, highly available product
delivered fresh on a door-to-door basis by mobile 2-wheeler vendors (Murray, 1999 b).
By contrast, very little of the production from the seasonal tanks enters commercial
markets, due to negative consumer quality perceptions associated with such fish. Most is
used instead for local consumption.
Traditional communal fishing practises and taboos formally designed to both restrict
access and preserve stocks have become eroded along with the community-based
institutions that contributed to their enforcement. They endure in part only as a
consequence of the priority accorded to bathing rather than fishing. Direct efforts to
enhance or manage the fisheries in any of the tanks investigated were restricted to very
occasional, individually sponsored, movements of wild brood stock. Most of the fisheries
are casually exploited by a small number of farmers living around the tank . Full open-
access status is only curtailed by a residual of weakly enforceable customary rules and
2 Refers to results obtained from Anamaduwa and Giribawa regions (Murray & Little, 2000) 3 Based on the study of two cascade systems, Danduwellawe and Pahala Diuluwewa (Murray et al, 2000)
15
norms favouring other priority uses. Most fishing efforts take place during the dryer
months (June –July).
The major common rule relating to seasonal tank fisheries is a prohibition on gill, seine
or cast-net fishing during the dry season to preserve the quality of any residual water for
bathing.
In terms of fishing method, a variety of selective and non-selective methods are used. The
most common one is gill netting (2” stretched mesh size). Passive fishing is rare, with
the exception of the collective harvesting period when rows of gills nets may be left in -
situ and rechecked over a number of days, this is due to the risk of leaving value gear
unattended. Recreational fishing is often practice by children, using hook and line
(Murray, 1999).
1.7.5 Aquaculture
Freshwater fish species used at present in fish culture are the Nile tilapia (O. niloticus),
red tilapia, the common carp (Cyprinus carpio), Indian major carps (Labeo rohita,
Cirrhinus mrigala and Catla catla ), grass carp (Ctenjopharyngodon idella ), big head carp
(Aristichthys robilis), silver carp (Hypophythalmichthys molitrix), and the indigenous of
Labeo dussumberi. At present the required number of Labeo dussumberi fry for culture
purposes are obtained through artificial breeding. Culture of carnivorous species such as
snakehead is not popular in Sri Lanka due to high production cost, and slower growth rate
compared to omnivorous or phytoplanktivorous species (Nathaniel, 2000)
Table 2. Annual Aquaculture Production
Sub-Sector 1997 1998 1999
Aquaculture* 27 ( metric tons) 30 (metric tons) 31 (metric tons)
(Source: Ministry of Fisheries and Aquatic Resources Development, Sri Lanka)
*Inland sector, coastal brackish water prawn and cultured prawn production.
16
In 1995 a new policy was established by the Minister of Fisheries to support inland
fisheries activities, which result in the creation of an aquaculture development division.
In this new division the major functions are seed production, stocking of water bodies,
training of personnel in aquacultural practices, development of adaptive research,
creation of awareness of environmental aspects and transfer of technology to the private
sector.
Seed production The State will assist and provide incentives to the private sector including the
purchase of fish seed from private farmers. The government will also promote the
participation of rural communities in seed production activities to ensure self-
employment and additional income to the rural people. As a part of the new strategy, the
government has already taken steps to make the aquaculture centers at Udawalawe and
Dambulla functional. Indian major carp will be bred in these stations and the fry of these
species will be handed over to the private sector for further rearing. The estate
management in the country will be encouraged to produce fingerlings in the estate tanks
through active participation of estate workers. The necessary inputs such as fish fry,
training facilities and financial assistance will be provided by the state. Part of the plan is
also to encourage the NGOs and agricultural farmers to produce fish fingerlings on a
small scale and establish community-based fish seed production centers. All necessary
assistance will be provided by the government (Minister of Fisheries and Aquatic Resources
Development, Sri Lanka).
Stocking of water bodies
Fish seed required for the stocking programs will be purchased from the farmers.
Participation of fishers cooperatives in the production of seed in the major tanks will be
encouraged. People's participation in resource management
Considering the common property nature of the reservoirs, active individual participation
will be ensured by co-operative societies, which will be organised where they do not
already exist. Similarly, in the case of seasonal tanks, appropriate organisations will be
17
formed to involve the participation of local inhabitants in resource management (Minister
of Fisheries and Aquatic Resources Development, Sri Lanka).
Incentives
Appropriate incentives such as tax holidays, duty free imports and proportionate
reduction in lease rentals, are envisaged for the promotion of aquaculture ventures.
(Ministry of Fisheries and Aquatic Resources Development)
1.8 Macrophytes
Macrophytes are the conspicuous plants that dominate wetlands, shallow lakes, and
streams. Macroscopic flora include the aquatic angiosperms (flowering plants),
pteridophytes (ferns), and bryophytes (mosses, hornworts, and liverworts). An
aquatic plant can be defined as one that is normally found growing in association with
standing water whose level is at or above the surface of the soil. Standing water
includes ponds, shallow lakes, marshes, ditches, reservoirs, swamps, bogs, canals,
and sewage lagoons. Aquatic plants, though less frequently, also occur in flowing
water, in streams, rivers, and springs (Stern, 2000) Aquatic macrophytes play a vital role in healthy ecosystems. They serve as primary
producers of oxygen through photosynthesis, provide a substrate for algae and
shelter for many invertebrates, aid in nutrient cycling to and from the sediments, and
help stabilize river and stream banks.
Biological filtration is an increasingly popular method of sewage treatment; some
aquatic plants are being used to remove nutrients and reduce concentrations of
phosphorus and nitrogen from raw sewage or from effluent sewage treatment
facilities. Aquatic plants are also able to absorb other substances, including pollutants
such as phenols (Kaufman, 1989).
Aquatic plants supply a wide variety of wildlife with food and suitable nesting
habitats. Some, even help to control pest populations; duckweeds are known to
reduce mosquito numbers, which has the added benefit of decreasing the incidence
of certain insect-borne diseases.
18
However, humans do not always consider plants to be so beneficial. Flooding of
agricultural land is a concern for many that farm on or near a watershed and plants
can play a significant role in creating these problems. As macrophyte biomass
increases, the mean water velocity of a river decreases. If river discharge is constant,
such a reduction in velocity will raise the water level, thereby presenting the
possibility of overflowing banks or raising water tables (Kaufman, 1989).
Fishing and navigation is another concern as tall emergent plants can prevent access
for shoreline fishing. Submerged species can also spoil the gravel spawning beds of
some fish (salmonids, in particular) and high densities of photosynthesizing
macrophytes are capable of causing large fluctuations in oxygen; this can stress many
fish species. Similarly, fish mortality may ensue when photosynthesis does not exceed
respiration (under prolonged hot and cloudy conditions), thus resulting in oxygen
depletion (Kaufman, 1989).
While some aquatics deter certain disease-carrying organisms, others provide an
ideal habitat. Several human diseases are transmitted through intermediate hosts that
are either dependent upon certain macrophytes for completion of their life cycle or
inhabit stagnant water resulting from the obstruction of water-courses by vegetation.
Schistosomiasis (African sleeping sickness) is one example; the intermediate host is
an aquatic snail that lives among aquatic vegetation (Kaufman, 1989)
. 1.8.1. Macrophytes of Sri Lanka The great abundance of surface water along the whole Sri Lankan geography, mainly in
the form of man made reservoirs (tanks), toge ther with the high level of water
interchange between water bodies, makes an ideal ecosystem for the subsistence of
aquatic plants.
Sri Lanka water bodies, especially man made reservoirs, are in fact partially or totally
encroached by a wide variety of indigenous and introduced aquatic plants.
The increasing prevalence of many aquatic weeds is, in fact, the result of human impact.
The nutrient enrichment of water bodies due to the run off of fertilizers encourages
growth and multiplication of algae and aqua tic plants to such a degree as to make them
noxious weeds.
19
At present in Sri Lanka, Salvinia and Eichhornia and to a lesser extent Limnacharis
flava, are the more troublesome weeds. Salvinia covers about 12000 ha of swamp and
paddy lands, and Eichhornia about 400 ha. (Dassanayake in Junk, 1973)
The spread of aquatic plants through the different water bodies has mainly the following
impacts:
1. Aquatic weeds reduce the flow of water in irrigation and drainage channels.
2. They sometimes block gates, points of water intake, as in power generating
stations and cause flooding.
3. Dense growths of Eichhornia and Pistia are said to harbour larvae of mosquitos
including vectors of filaria.
4. In paddy fields they reduce yields by competing with the paddy for light and
nutrients.
Some of the aquatic weeds are used by the local people for various purposes. The uses
mentioned below work against their control: 1. Leaves of Limnocharis flave and
Monochria vaginalis are eaten as a pot herb by some people. 2. Flowers of Eichhornia are
used as offerings in Buddist temples, and are often locally sold outside temples. 3. Fresh
salvinia is used as packing material for fish. This practice is largely responsible for its
spread from one region to another. 4. Salvinia and other aquatic macrophytes are used for
making compost. Salvinia is comparable to cattle manure in nutrient composition and it
can be used for compost making, which may help in its control if planned properly
(Dassanayake in Junk, 1973).
18.2. Noxious water vegetation in Sri Lanka
The main types of aquatic plants found in large water bodies along Sri Lanka are found in
the form of:
Floating weeds
Eichhornia crassipes, Salvinia auriculata and Pistia stratiotes are the
three most troublesome floating weeds.
20
Emerged weeds
Typha javanica (bull-rush weed) and Limnocharis flava (water cabba
ge), are widely occurring weeds of this type in the country.
Submerged weeds
Hydrilla, Vallisneria and Utricalaria are the most common submerged
Weeds.
Bank weeds
Lagenadra ovata (Ketala) Typha javanica (Hambu)
Algae
These do not cause any serious problem in Sri Lanka, but few sporadic
cases of poisoning of cattle have occurred and the blue-green algae are
suspected to be the causal organism.
In spite of heavy expenditure and efforts of most farmers directed towards the destruction
of water hyacinth, it has not been possible to control it satisfactorily. Experience with
other aquatic weeds such as Salvinia and Pistia has also been unhappy and very costly to
farmers and to the State. Government appeals and the legal machinery have failed due to
the irresponsibility of some farmers and land owners (Junk, 1973).
Figure 5. Tank cover with aquatic plants.
21
Figure 6. Nyphacea lotus.
22
Objectives
This study had as the main aim the enhanced management of seasonal tank fisheries. In
order to achieve such an aim, two factors have been studied: bio -physical and socio-
economic.
The principal objectives are:
1.Bio-physical
1.1 A review of the present tank classification, which aimed to obtain a more accurate
and explicit tank classification with respect to the seasonality, water input and
location within the cascade system. The new classification will allow the
identification of potential aquaculture development in quick an accurate manner.
1.2 The trends in water use by the surrounding livelihoods in seasonal tanks and an
assessment of the resources flow, with respect to primary productivity and water
availability.
1.3 The impacts of macrophytes on the tanks, to assess the role of these aquatic species
in such environments and on the surrounding livelihoods with a special attention to
new introductions like salvenia.
1.4 The effects of tank rehabilitation over macrophytes encroachment, to assess it’s
viability as a control method.
2. Socio-economic
2.1 The location in the watershed with respect to different resources and distance from
important infrastructures such as schools, hospitals, etc., to assess their impact on
the role of tanks and their value in people’s livelihoods.
2.2 The assessment between geographical location and wealth, as well as social factors
such as caste.
The previous objectives will identify the level of dependence on natural resources within
the watershed and the possible social conflicts.
23
2. Methods This report has followed a wide variety of methods and techniques, due to the abundance
of different areas directly involved with the main project objective, the enhancement of
management in seasonal tanks for aquaculture. The range of areas covered includes
physical, biological, social, economic and marketing aspects. The collection of
information and the following analysis for each area required different methods to
achieve accurate and reliable results.
Three main tasks have been carried out during the project, covering the areas already
mentioned.
2.1 Data collection
The first task or data collection has been mainly carried out in the field by a group of
researchers, during the past 2 years. Collection of primary and secondary data from the
tanks and the surrounded livelihoods has been the main aim of this research group4.
In addition to the collection of primary data by the already mentioned researchers, 3 to 4
days a week over two months were spent in the field collecting data in order to become
familiar with the methodology used as well as the study areas and to assess the accuracy
of the techniques carried out in the field. Other additional data related to macrophytes
was also collected during the course of the two 2 months.
2.1.1 Primary data
Physical primary data has been collected, in order to configure the status and trends of the
different physical factors related to tank hydrology. This task was mainly carried out by a
research assistant, having as main task water quality parameters data collection and
analysis, which included pH water analysis, dissolved oxygen analysis, suspended solids
analysis and evaporation rate analysis. In addition water level measurements from all
tanks, and weekly measurements from key tanks were collected.
4 Research group: PHd, student: Francis Murray, field staff: Priyantha Jayakody, Yasantha Nawarathne, Bandara Samarakoon.
24
Data collection was carried out in the field on key villages and related tanks. The
methodology used is often known as participatory field work, where a wide variety of
tools have been developed, employed systematically in what are known as Participatory
Rural Appraisals and Rapid Rural Appraisal, the major distinction lying with the degree
of farmer participation. The variety of tools used in this project are listed in Box 1
(Murray & Little, 2000)
The major uses of water bodies as well as the key constraints to the introduction of
aquaculture into village tanks were identified in community meetings and ranked and
scored in order of priority by farmers. To asses the wider impacts of water and land
management practices, appraisal was extended to the cascade level using individual farm
and catchment walks and key informant interviews. Farmers were questioned about
historic trends in water availability, tank system operation, maintenance and management
(Murray, 1999 b).
Box 1: Participatory Rural Appraisal Tools used in the project field research (after Townsley, 1996 in Murray & Little, 2000) Secondary data sources: Used as in conventional research Semi-Structure Interviews: Instead of a formal questionnaire, interviews use a checklist of questions related to each topic of interest. This is a flexible method allowing for the follow up of interesting topics arising during the interview. Interviews can be conducted with Key informants (people with specialist knowledge about a topic or third parties), with individuals or groups. Ranking and scoring: Issues or items are placed in order of importance (ranking) or allocated a proportion of a limited number of points (scoring). Used to identified the priorities of a community when carried out with individuals. Wealth ranking: Used to investigated local perceptions of wealth grouping within the community. Parameters used in the classification identified by villagers, thus revealing local indicators and criteria of wealth. Diagrams and maps: Used to simplified and present complex information in a easy to understand format. Often used to stimulate the interest of villagers and increase their participation. Resource flow diagrams: To show the flow or resources (e.g. water, crops, animals, plant/animal residues, agro-chemicals, money) between the different components of a system. Watershed maps: To show the ownership of land holdings and waterbodies within a watershed. Seasonal diagrams: To show patterns of rainfall, food availability, workload, credit etc.. over a year. Venn diagrams : To show the relationships and connections between different individuals institutions in a community. Social maps: To show distribution of all village households along with demographic and resource ownershi details (i.e. gender balance, caste , wealth status, literacy, land ownership etc.) Activity charts: To chart the activities carried out by individuals or groups within a fixed time period
25
2.1.3. Assessment of importance of macrophytes
This particular section of the study focused on the impacts of macrophytes on the
surveyed tanks and the surrounding livelihoods, to compliment and add a greater
accuracy to the data already collected by the research group. Two main tasks were carried
out:
1) Collection of primary data, through a survey questionnaire, based on six main
questions (Box 2), and carried out in three representative cascade systems using as key
informants, mainly farmers and fishermen from the surrounding villages.
2) Taxonomic identification of the main species found at the tanks. Consultation of the
main botanical local literature sources, mainly at Peradeniya University library
(Kandy, Sri Lanka), in order to classify the species found in the field and their main
characteristics (Appendix Number 6).
The level of encroachment of aquatic macrophites was estimated for the 92 tanks in terms
of percentage area covered and differentiating the main aquatic plant species present
(Ollu/Nelum, salvinia, water hyacinth, submerged plants and others). Respondents were
asked to estimate cover for the last two main monsoon seasons (Maha and Yala) over
the last two years.
New methods for area estimation and macrophytes distributions were tried. Such
methodology was based on the creation of a standard model for area estimation, which
will give an approximate estimation of the area covered by macrophytes. But due to the
lack of time and also resources such methodology had to be abandoned.
Box 2: Macrophytes questionnaire 1) Which are the main macrophytes in the tank? 2) When did the different macrophytes first appear? 3) Do they have the impacts on fishing, bathing or irrigation? If yes, which ones? 4) How did the infestation start? 5) Has any increase in mosquitoes occurred with the increase of macrophytes? 6) Is there any control method, presently used? 7) Are the macrophytes used for any purpose?, if yes, which ones?
26
2.2. Data organization structure As a result of the work mainly done by the research group and the extra data collected
during the length of the study (2 months) in the field, a series of spread sheets were
created, which contained a wide variety of data. Seven spreadsheets, which mainly
covered hydrological aspects, water management and uses, livestock characteristics,
fisheries aspects, social and economic issues, from the 92 tanks surveyed and the related
villages surrounding the tanks. A special distinction has been made in the data collected
during the two main seasons (Maha and Yala).
Due to the extension of the data recorded and to the different personnel involved with the
data entry, data clearing was needed, to tidy up the spreadsheets and facilitate the
understanding and handling of the information collected. The output from such data
clearance and the differences from the original raw data can be observed in the Appendix
7 (disc attached). Also the methodology followed during the data clearing, which
involved between others, grouping, reclassification, etc. is summarized in Appendix 5.
2.3. Data Analysis
Once the data collected was cleared and tidied up, a selection of the relevant data from
the spreadsheet was carried out, mainly spotting the information necessary to reach the
proposed objectives (Introduction, section 1.9).
Analysis of selected data was carried out using two main statistical packages, Excell’98
and SPSS version 9. Descriptive statistical methods were the principal type of analysis
used, aiming to obtained a clear view of the situation, task, which have not been done
before. The use of simple descriptive methods was chosen, because: no data analysis was
done previously, therefore demonstration of the main hypothesis was needed beforehand,
to later carry on with more complex methods.
Following the use of descriptive statistical methods. More advanced statistical analysis,
using mostly Chi square tests on count and univariate and multivariate analysis of
variance (ANOVA) with or without interaction depending on the data analyzed were
used. Normality and Constance variance tests were also run to assure the analysis results
reliability and it accuracy. No Post hoc analysis was carried because the amount of data
used was insufficient to obtain reliable results.
27
3. Results
The following results covered a wide range of subjects all related to the success of fish
culture in different tanks, therefore most of the results have a common denominator,
which is the tank classification, based mainly on water-input and seasonality factors.
3.1 Tank classification
The cascade systems vary in complexity, although two main configurations are presently
used to classify cascade systems (Linear and Branch5), still there is no clear classification
which distinguishes accurately the main characteristics of each tank in the system.
So far the main system currently used to classify tanks is based on the tank seasonality
(Drying frequency6), although this classification (Table 3) describes in a concise manner
the main limiting factor (water availability) for aquaculture development, it still lacks of
information related to geographical location and size.
Murray, (1999 a), came up with a new system to classify the different tanks based on
their position within the cascade system and their water input and retention. This system
distinguishes three main types:
Radial tanks: Mostly at the top of the cascade with its catchment area as only
source of water.
Axial 1: Receives water from 1 or more Radial tanks (intermediate location)
Axial 2: Receives water from axial 1 tanks and radial (Bottom of the cascade)
Together, the mentioned classifications give a general idea about the tank characteristics
but based on the field experience still there are still no clear links between these two
classifications.
5 Linear cascade system: Series of tanks linearly configure in the axis Branch cascade system: A main axial configuration fed by multiple outer tanks 6 Dry tank: when water level is not enough to sustain fish life.
28
Tank Type Drying Frequency
Perennial Have not dried in living memory
Semi-seasonal Dries one or two times every 5 years
Seasonal Dries two or three times every 5 years
Highly seasonal Dries every year
Using the above classification systems as main source, a new classification has been
created which will allow identification of almost any tank characteristics by just looking
at their location in the cascade and their relative size.
Using Murray, (1999), classification as the main coding system, few adjustments and
inclusions were made based on the data analysis (Figures 7,8) and field observations.
As result four main tanks are found in any cascade system:
Radial : Small (generally <4.8 ha), mostly highly seasonal tank, generally at the top of
the cascade, with its catchment as only source of water. Does not receive water from any
other tank.
Axial 1a: Small (<4.8 ha) and highly seasonal, which receives water from only one
radial tank.
Axial 1: Receives water from 2 or more radial tanks, seasonally variable, if >4.90 ha
is highly seasonal or seasonal.
Axial 2: Receives water from one Axial 1 tank and 1 or more radial tanks, mainly
perennial and semi-seasonal.
Axial 3: Large tanks, which receives water from 2 or more Axial 1 tanks, 1 or more
Axial 2 tanks and any radial tanks, mainly perennial, rarely semi-seasonal.
The graphical explanation for such a new classification is backed up by a series of
correlations run between tank seasonality, water input and maximum water spread
(Figure 7,8).
Table 3. Tank Classification based on water availability
29
Looking at the tank distribution (Figure 7), it can be observed that the amount of highly
seasonal radial tanks (89.4% of all the radial tanks (figure 8), followed by 7.2% seasonal
(Figure 8). Therefore except for literally 10% of the total radial tanks (57), an assumption
has been made which describes radial tanks as mostly highly seasonal (dry every year).
In terms of “Axial 1a” tanks, the relation with seasonality is even clearer where 100% of
all of them are highly seasonal (Figures 7,8).
On the other hand, the next tank type, Axial 1 tanks, which are generally located at the
middle of the cascade system, present a wider variability in terms of seasonality.
In order to get an accurate estimation of Axial 1 tank characteristics from just looking at
the map; the size factor is going to be crucial. A supplementary correlation between size
and seasonality has been made (Figure 8), this correlation gives as a result the close
association between seasonal tanks (highly seasonal and seasonal) and size, which are all
smaller than 4.9 hectares. Therefore after identifying an Axial 1 tank from it location and
water input (receives water from 2 or more radial tanks), if the tank is smaller than 4.9, it
is going to be a highly seasonal or seasonal tank, if it is bigger it would be perennial or
semi-seasonal and these represent 70 % of the total Axial 1 tanks (Figure 7).
30
Figure 7. Total tank distribution (%), from each tank type, in terms of seasonality Patterns (HS:highly seasonal, SS: semi-seasonal, P: perennial, S:seasonal). Using chi-square a significant relationship between tank type and seasonality was shown
(P<0.05) (Table 7, Appendix 8), where tank types tend to have particular water
availability characteristics.
Going downstream in the cascade system, tanks are getting bigger in size and less
seasonal; the next type of tank, Axial 2 are mainly perennial (57.14%), followed by 28.5
% semi-seasona l, and the rest (14.2%) are highly seasonal tanks, which are smaller than
4.9 hectares.
Finally and at the bottom of the cascade, generally the biggest tanks in the cascade (>10
ha) (Figure 8), the Axial 3 tanks are mostly perennial (81.7%), although some of them are
semi-seasonal (18.18%).
The presented classification is able to define clearly the tank characteristics by just
looking at the map. Still semi-seasonal tanks are not clearly defined, but in terms of
highly seasonal, seasonal and perennial tanks the relationship with the water input
classification and location is quite accurate.
Correlation between water input and seasonality
0.0
20.0
40.0
60.0
80.0
100.0
Axial 1a Radial Axial 1 Axial 2 Axilal 3
Tank Type
Tan
k ab
un
dan
ce (%
)
HSSSPS
31
Figure 8. Seasonality and maximum water spread relationship ( HS:highly seasonal, SS: semi-
seasonal, P: perennial, S:seasonal. n = 92). The relationship between maximum water spread and water seasonality is significant
(P<0.05) (Table 8, Appendix 8), where side of the maximum water spread has particular
water availability characteristics.
3.2 Natural fisheries productivity 3.2.1 Natural production by tank type Two main types of fishing take place in the cascade systems surveyed:
1) Collective fishing, which takes place during the dry season once the tanks reach a
minimum water level, where the fish habitat is reduced to shallow waters, making
them more vulnerable and therefore increasing the fishing catch. This activity is a
community activity, in which the majority of the village people participate; even the
non-participants receive a small amount of the total catch.
Seasonality and maximum water spread relationship
0
10
20
30
40
< 2.5 2.5 < 5 5 < 10 >10
Maximum water spread (ha)
Nu
mb
er o
f ta
nks
PSSSHS
32
2) Pre-collective fishing, defined as regular fishing act ivity, which takes place year
round, mainly by fishermen and children, often for recreational purposes
Although some restocking has been done mainly in seasonal tanks, the majority of the
tanks surveyed rely on it’s natural production.
The fisheries production data obtained from the different tanks during the year 2000, are
a reflection of the water availability and the fishing effort, which are the main limiting
factors. Although the data source (village fishermen recalls), is not the most accurate
source, such data has been cross checked with other related data like species catch, giving
an acceptable general idea about the tank production (Figure 9).
Collective fishing (Figure 9) is the main method for fish harvest, compared to traditional
fishing (pre-collective fishing).
Figure 9. Average fisheries annual production from two types of fishing: collective fishing and pre-collective fishing at the different tanks. Clear differences (P<0.05) in production can be observed between the two types of
fishing practice, as well as at the different types of tanks (P<0.05) where the production
Average fisheries annual production of fish from tanks by category
0.050.0
100.0
150.0
200.0
250.0
300.0
Radial Axial 1a Axial 1 Axial 2 Axial 3
Tank type
Ann
ual P
rodu
ctio
n (K
g/ha
)
Fisheries Production from collective fishing (kg/ha)Fisheries Production from pre-collective fishing (kg/ha)
33
results are quite significant (Table 9, Appendix 8). On the other hand the interaction
between fish type and tank type was not significant (P=0.058).
Fisheries production from collective fishing at the different tanks is greater in the Axial 1
tanks, although the unusual total drainage of a big tank has to be mentioned, which
produced a catch of 3000 kilos. Apart from Axial 1, the radial tanks have an average of
64.4 kilos per hectare, followed by perennial tanks with 47.9 kilos per hectare.
In terms of pre-collective fishing, Axial 1 tanks are the more productive (32.6 kg/ha),
followed by axial 1a (20.5 kg/ha) tanks. Looking at the production in perennials tanks
(4.94 Kg/ha) an obvious issue that can be raised is the size factor, the bigger the tank, the
deeper, therefore the probabilities of catching fish decrease.
Looking closely to the fisheries production, 5 main species are fished, two types of
tilapia7 , climbing perch, snakehead and small indigenous species.
Tilapia and snakehead are the species mostly present in all tanks, representing
approximately between 50-60 and 30-40 percent of the total catch in each tank
respectively (Figure 10). Also present in all the tanks, although in smaller percentage, the
small indigenous species, appear to be the third more abundant prey (between 3-8%,
increasing to a 21% in the radial tanks).
On the other hand, climbing perch, although quite often caught, appear to be restricted to
mainly Axial 1 and 3 tanks (2.5 and 1.25 % respectively).
Due to the unavailability of data mainly from radial and Axial 1a tanks the above results
are subject to discussion and further study. For the same reason, no analysis have been
carried out over pre-collective fishing, from which the data was insufficient to generate
acceptable results.
7 Due to the informant’s inability to clearly identified Oreochromis. mossambicus from Oreochromis niloticus, no distinction has been made between them.
SIS:
34
Figure 10. Collective fishing main caught species and it distribution at the different tanks. (SIS: Indigenous Species) No significant interaction (P=0.7) between tank type and fish species distribution has
been found (Table 10, Appendix 8), all the tanks tend to have the same types of fish
species. Also no clear difference (P=0.931) has been found between the different tank
types, but significant differences (P<0.05) can be observed in terms of species abundance
within every tank (Table 10, Appendix 8).
3.3 Macrophytes Macrophytes are without any doubt an important aspect in the tank environment, mainly
due to their presence in nearly all the cascade systems.
Although the aquatic plant diversity in such tanks is quite broad, 4 main aquatic plants
are more abundant and are the ones with more interaction with the environment and the
surrounding livelihoods. Such species are: Nymphacea lotus and Nelumbo nucifera
(figure 14-12) locally known as Ollu and Nelum respectively, Salvinia molesta ,
Catch species distribution from collective fishing
0.0020.0040.0060.0080.00
100.00
Radial A1 A2 A3
Tank type
Tot
al C
atch
(%)
SISSnakeheadClimbing perchTilapia sp.
35
commonly known as salvinia (Figure 11), Utricularia vulgaris and Ceratophyllum
demersus locally known as parsy and veru (Figure 13).
Figure 11. Tank cover with salvinia sp. Figure 12. Tank cover with Nelumbo nucifera
Figure 13. Utricularia vulgaris Figure 14. Nymphacea lotus.
36
On average from the 92 tanks surveyed, Ollu and Nelum (Nymphacea lotus and Nelumbo
nucifera) are the most dominant species present, covering on average of 26.85 % of the
tank area (figure 15), after those species the emergent grasses cover in average a 10 % of
the tank total area, followed by salvinia (3.69%). The water hyacinth (Eichhornia
crassipes) although quite wide spread in other parts of the country, can barely seen in the
surveyed tanks covering only 1.22% of the total tank area. Other species, cover only
0.63% of the total area.
Figure 15. Mean percentage of area covered by different macrophytes within the 92 tanks. Significant differences (P<0.05) between groups of different macrophytes species were
observed in terms of abundance and distribution (Table 11, Appendix 8), where
Ollu/nelum are the most abundant species (Figure 15).
Percentage of water cover by specific macrophytes
0.63
10.06
1.223.69
26.85
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
Olu / nelum Salvenia Hyacinth Emergentgrasses
OtherSpecies
Main macrophytes present at the tanks
Per
cent
age
of w
ater
are
a co
vere
d
37
Water availability and physical conditions in the different tanks appear to determine the
presence and abundance of the already mentioned aquatic plants; therefore each tank has
a characteristic encroachment (Figure 16).
In terms of Ollu and Nelum (Nymphacea lotus and Nelumbo nucifera) encroachment has
a greater presence in the Axial 1a tanks covering the 52.8 % of the total tank area, also
close to 50 %, in the Axial 3 tanks these species are quite common (40.5%). In the Axial2
and radial tanks the encroachment of such species is reduced to 32.5 and 26.5 %
respectively, followed by axial 1with 20% encroachment of Ollu and Nelum.
The second more abundant aquatic plant group are the emergent grasses, which covered
17.8 % of the Axial 1a tank total area, followed by the Axial 3 tanks with 13,3%
encroachment, which decreased in the Axial 2, radial and Axial 1 tanks.
On the other hand, although not present in all the tanks, salvinia encroachment is quite
high in the Axial 3 and Axial 2 tanks (13.8 and 9.5 %).
Figure 16. Macrophyte encroachment in tanks by type, from 92 tanks.
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Radial Axial 1a Axial 1 Axial 2 Axial 3
Tank Type
Mea
n p
erce
nta
ge
of
wat
er a
rea
cove
red
Olu / nelum Salvenia Hyacinth Emergent grassesOther Species
38
Significant interaction (P<0.05) has been found between tank type and macrophytes
species (Table 12, Appendix 8), where species presence varies depending on tank type.
Also differences (P<0.05) in terms of macrophytes abundance within the tank can be
observed, as well as (P<0.05) the total area covered by macrophytes in the different tank
types (Table 12, Appendix 8).
The above results are based on data taken from the field where visual estimation of the
total and species encroachment was carried out in each tank. No other method was used
to estimate tank encroachment, and due to the methods accuracy the results are not as
accurate as they could be, if applying for instance, aerial photography analysis systems.
In order to obtain more specific status data macrophytes encroachment and its impacts on
the tank and surrounding villages, a questionnaire was carried out.
From such questionnaire and collection of specimens plus later taxonomic identification,
11 species were identified as the main species at the tanks surveyed (26) from three
different cascade systems. The species below can be classified in 4 groups: a) rooted, b)
floating, c) submerged and d) aquatic grasses.
The taxonomic characteristics of each specie found in the field are indicated below
(Table 5), plus some general information in Appendix 6.
Table 4. List of Aquatic plants found in the field and their common names
B o t a n i c a l n a m e L o c a l n a m eA p o n o g e t u m c r i s p u s K e k e t i aC e r a t o p h y l l u m d e m e r s u m V e r uE i c h h o r n i a c r a s s i p e s J a p a n j a p a r aI s e h e g l o b o s a Batade l l aN e l u m b o n u c i f e r a N e l u mN y m p h o i d e s i n d i c a C o m o d uN y m p h a c e a l o t u s Ol luN y m p h a c e a s t e l l a t a M a n n e lSa lv in ia au r i cu la ta S a l v i n i aUtr icu la r ia vu lgar is P a r s iEleochar i s duc i s B o r u p a n
39
Many other species were seen at the tanks visited, but because of relatively little
abundance and little impact over the communities around the tanks, were not included in
the survey. As a result from the survey a few common main impacts were identified:
Obstruction for fishing, bathing and irrigation and reduction of tank capacity.
On the other hand, these macrophytes supply the livelihood with sources of food for man
as well as for livestock, medicine and decoration, besides other uses. A common
denominator between all the tanks surveyed is the fact that no permanent control method
is applied in order to manage the macrophytes infestation, just temporal clearance for
bathing and fishing. Such control methods were mainly manual removal of macrophytes
by villagers, normally in a collective effort. More detailed information about the survey
results is given in Table 5
3.4.1. Production and water tank area cover with macrophytes The direct impacts of macrophytes infestation on fisheries production needed to be
assessed (Figure 17,18). The interaction between those two factors is crucial for fish
production. In the study area a slight correlation can be observed between the fisheries
production and macrophytes infestation, but such a correlation is not enough to strictly
relate fish production to macrophytes infestation levels. The relationship is very similar
between the fisheries production from both pre and collective fishing.
40
Figure 17 . Aquatic encroachment and fisheries productivity correlation from pre-collective fishing production.
Figure 18. Aquatic encroachment and fisheries productivity correlation from collective fishing production.
Tank product ion and macrophytes encroachment (co l lec t ive f ish ing)
y = -1 .374x + 132 .64R 2 = 0 .392
0.0050.00
100.00150.00200.00250.00300.00
0 2 0 40 6 0 8 0 1 0 0
Aquat ic weed sur face a rea covered (%)
Fis
h ha
rves
t
(Kg/
ha/y
ear)
Fisheries tank production and aquatic encroachment correlation (Pre-Collective fishing)
y = -1,147x + 85,698R2 = 0,3676
0,00
50,00
100,00
150,00
200,00
250,00
0 20 40 60 80 100Aquatic weed surface area covered(%)
Fish
har
vest
(K
g/ha
)
41
Table 5. Uses, impacts, introduction agent and control methods from the main macrophytes in 20 tanks Botanical Name Common
Name Total Presence in Tanks (%)
Uses Impacts Introduction agent
Mosquitoes increase
Control Method
Floating macrophytes
Salvenia molesta and auriculate
Salvenia 46 No uses Obstruction for fishing, bathing and
irrigation, reduction of tank capacity
Fishing nets, spill events
No Irregular partial removal, limited
to bathing fishing areas.
Eichhornia crassipes Water hyacinth 23 Livestoc k food Obstruction for fishing, bathing, reduction of tank
capacity
Livestock No Irregular partial removal, limited
to bathing fishing areas.
Rooting macrophytes
Nelumbo nucifera Nelum or water lilies
62 Decoration (flower), food (Seeds and
stems)
Difficult to remove due stem's spines
(fishing), reduction of tank capacity
Livestock, Man No Irregular partial removal, limited
to bathing fishing areas.
Nymphacea stellata & Nymphoides indica
Mannel & Comodu
62 Food (roots), medicine
Minimal impacts Livestock, Man No No
Nymphacea Lotus Ollu 92 Decoration (flower), Food source (Seeds,
roots and stems), Medicine for diabetes
(seed)
Obstruction for fishing and bathing. Reduction of tank
capacity
Livestock, Man No Irregular partial removal, limited
to bathing fishing areas.
Aponogetum crispus Keketia 92 Food (roots & flower), Minimal impacts Always been present
No No
Diya Simbula 23 No uses Minimal impacts No
Grass macrophytes
Eleocharis dulcis Borupan 55 Carpet material Minimal impacts Livestock No No
Isehne globosa Batadella 60 No uses Obstruction for fishing (Gill netting).
Fishing No Irregular partial removal, limited
to bathing fishing areas.
Submerged Macrophytes
Ceratophyllum demersum
Utricularia Vulgaris
Veru
Parsi
75 No uses Obstruction for fishing and bathing and blocks sluice
Fishing, spills No Irregular partial removal, limited
to bathing fishing areas.
43
3.4.2. Rehabilitation One of the control methods used in tanks to eradicate or control macrophyte infestation is
tank rehabilitation, not only with the purpose of eradicating the aquatic plants, but also to
increase tank capacity.
The major type of rehabilitation used is desilting the tank. A series of tanks in the
surveyed area have undergo treatment. The result is the partial eradication of the
macrophytes infestation (Figure 19), although the effect seems to be temporary rarely
lasting more than 3 years.
Of the tanks which have been fully desilted, 90% have an encroachment level below 31
percent, of which 63.3% have been desilted in the past 3 years. On the other hand 60% of
the tanks partially desilted had an encroachment below 31 %, of which 46% were desilted
in the past 3 years.
In contrast those tanks in which no desilting has taken place, show a diverse
encroachment level, mostly high.
Figure 19.Effects of desilting over the macrophytes encroachment. A significant difference (P<0.05) has been found between the percentage of area covered and the degree of desiltation to which tanks were exposed to (Table 13, Appendix 8), although data available was based on a small number of cases. * This test may not be valid because 4 cells (44.4%) have expected count less than 5 (Table 13, Appendix 8), but looking at the plot (Figure 19) appears a clear difference in percentage within different rehabilitation degrees
Impacts of Desiltation over the macrophytes
0%
20%
40%
60%
80%
100%
Full Partial None
Degree of rehabilitation
To
tal p
erce
nta
ge
of
Tan
ks s
urv
ey
61-10031-60<31
Percentage of tank area cover by macrophytes
44
3.4 Poverty The definition of poverty is a very wide concept, which varies within the different
countries, cultures, villages, etc. In order to target those groups in the project area
context, a few factors or poverty indicators have been looked at according to the main
economic and social values found at the project area.
A series of factor indicators of wealth, were looked at:
a) Isolation, or distance from main infrastructures, like main road, schools, hospitals,
etc.
b) Ownership, amount and types of land owned (ex: paddy land, etc.)
c) Labour the type of labour in terms of benefits obtained and the durability.
d) Housing characteristics, the type of house is a clear sign of economic status.
e) Caste characteristics, there is a common association of low cast with poverty due to
the their rights limitations within the community.
The above factors have been used to try to locate such groups within the cascade system
and establish whether a poverty-location relationship can be found in at the project area.
3.4.1 Isolation
The more isolated villages are from main confounding infrastructure the less accessible
are basic needs such as food sources, medicines, clothes etc, as well as schools and
hospitals. Using the tank classification proposed in this thesis and some basic
infrastructures (main road, schools and hospitals) a location-poverty relationship was
investigated at (Figure 20).
No tangible relationship has been observed, since all main infrastructures tends to be
within the same range of distance from the different tank types (1 to 2-km difference).
45
Figure 20. Average distance to main infrastructures from the villages allocated at the different tanks.
No significance interaction (P=0.650) has been found between distance from
infrastructure and tank type (P=0.701)(Table 14, Appendix 8), where the distance is
similar from all the different tanks. On the other hand, significant differences (P<0.05)
were observed in the distance from the tanks to the different infrastructures (Table 14,
Appendix 8)
3.4.2 Ownership
Ownership8 of land, as well as the area size owned,area is a clear indicator of wealth,
giving the owner a stable source of food or economic profits. The more cultivated land
the greater the availability and variability of outputs. Lower in the watershed
8 Command area owner: ownership of land in general terms. Paddy local cultivators: ownership of paddy land.
Average distance to various types of infrastructure from the different tanks
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
MetropolitanRoad
Primary School SecondarySchool
Hospital
Dis
tan
ce (k
m)
RadialA1aA1A2A3
46
overpopulation is a common characteristic, new generations tend to settle upper in the
watershed, where there are less people, but the land is mostly privately owned (i.e.
Temples). Land type is an important indicator, for instance due to the high rice demand,
the ownership of paddy land gives a greater of wealth.
In this case a clear relationship can be observed between ownership and tank type (Figure
21).
As tank seasonality increased as well as the position in the watershed (towards the top),
(i.e: Radial and Axial 1 tanks), the size of land owned increased, whereas for larger
seasonal tank further down the cascade the area of land owned is smaller.
Figure 21. Distribution of land ownership opposed to paddy cultivators owners within
the different tanks.
A significant difference (P<0.05) was found between tank type and type of ownership
and command area owners (Table 15, Appendix 8)
Command area owners and local paddy cultivators at the differents tanks
0
20
40
60
80
100
120
Radial A1 A2 A3
Nu
mb
er o
f h
ou
seh
old
s
Command area ownersper haLocal paddy cultivators
47
3.4.3 Labour
Another source of economic stability is labour type, specially, in terms of sustainability,
whether is long term of seasonal. The reliability of seasonal jobs is an indicator of
economy stability. In the area project area such labour is known as “coolie labour”,
mainly consists of people who leave the village during the day to work in part-time jobs
in neighboring villages. Such labour can be observed (Figure 21) to increase as the
seasonality of the tanks increases, going from a 20% of the total population in Axial 1a to
5.6% in Axial 3 tanks and nearly zero in the Axial 2 tanks.
3.4.4 Housing Three types of housing characterized the villages in the study area. The main
characteristic was the house quality in terms of durability. Temporary houses, mainly
made of dry mud and palm roofs, are quite vulnerable to weather damages. Semi-
permanent houses, made of more durable materials (bricks), are less vulnerable to the
weather. Thirdly, permanent houses generally made of brick or concrete with stable roofs
made of tiles, are the last susceptible to damage.
This factor clearly is wealth indicator, where poverty is more common in villages where
more less durable houses are present.
In the project area 45% of the total households near radial tanks have temporary houses
(Figure 23), although over a 35% are permanent houses, it can be observed that
temporary houses increase towards the more seasonal tanks higher in the cascade system,
where at the Axial 2 the temporary houses represented 20% of the total houses, going up
45% at the radial tanks. Due to the higher population and social diversity, the percentage
of temporary around Axial 3 tanks houses is quite high (32%), but main house type is
permanent (68%).
48
Figure 22. Temporary labour distribution by category of tank. The importance of temporary labour (P<0.05) has been found to vary with tank category (Figure 22). 3.4.5 Caste Sri Lankan society has quite strong traditional values. Part of these values is the division
of society into different groups or castes, which are directly related with occupation. A
hierarchy based on rights and priorities define low and high casts. A possible
relationship between castes and residence near tanks has been investigated (Figure 23).
No clear relationship was observed. However, although the absence of lower castes at the
Axial 2 and 3 tanks and a decrease in the proportion of people in the farmer caste at the
radial and Axial 1a tanks was noted.
Temporary labour from living around different tanks
20
13.60
7.14 5.67
0.1505
10152025
A1a A1 Radial A3 A2
Tank Type
Per
cent
age
of th
e to
tal p
opul
atio
n
49
Figure 23. Distribution of type houses at the different tanks. Total percentage and total number of houses. A difference (P<0.05) between tank types and housing distribution can be observed
(Table 17, Appendix 8), as well as house type abundance for each tank type (P<0.05), but
no significant interaction (P=0.5) is found between tank type and housing in general
terms. Although some differences can be appreciated they are not statistically significant
(Figure 23).
Housing characteristics at the differents tanks
0%10%20%30%40%50%60%70%80%90%
100%
Radial A1a A1 A2 A3
Tank Types
To
tal P
erce
nta
ng
e o
f
ho
use
ho
lds
Perm Hses (No HH)
S Perm Hses (No HH)Temp Hses (No HH)
50
Figure 24. Caste9distribution at the different tanks. The cast classification given at the, side of graph is in hierarchy order from top to bot tom, being the higher cast. A significant interaction (P<0.05) is found between tank type and caste, variability
between the different tank types and the distribution of caste within each tank is also
significant (P<0.05)(Table 18, Appendix 8). Also abundance of the different caste within
the different tanks is significant (P<0.05).
9 Casts: Gobi= farmers (a, b, c, depending on the type of culture), Kumbara= Potters, Durai= horn players and supply carriers.
Caste and watershed position relationship
0
10
20
30
40
50
Radial A1a A1 A2 A3
Tank type
Ab
un
dan
ce (%
)
Govi AGovi BGovi CGoldsmithKumbaraDuraiGypsy
51
4. Discussion Aquaculture development in developing countries is a task that differs greatly from that
in western countries. This is mainly due to a series of economic and cultural factors. The
success of such enterprise in developing countries requires overall study of socio -
economic aspects as well as biological and cultural ones. Although no aquaculture
practices take place in the project area, the aim of the broader project is to develop
approaches to aquaculture based on seasonal tanks.
Many projects and studies have been carried out aiming to improve aquaculture
development in needy areas such as the Dry Zone, but most of them have failed to obtain
positive or sustainable results. The main reason for such failures is the limited scope
which those studies have focussed on. Most of such projects have looked at specific
aspects, for instance, biological aspects, socio-economic aspects, etc, but they failed to
interrelate the different aspects to obtain an overall view.
This study had as an main aim the interrelation of the most relevant aspects for future
sustainable development of aquaculture in the study area. Therefore a wide scope of
aspects has been looked at, covering physical, biological, social and economic conditions.
4.1 Physical aspects An understanding of the physical aspects is necessary since they are limiting factors.
Once such aspects have been identified and classified, a more precise view of resource
use is obtained. In the study area the potential for aquaculture is clearly identified with the use of the
tanks or man made reservoirs as a main resource. Due to the wide variety of tanks with
respect to location, water catchment and seasonality a base classification was needed
(Results 3.1). This classification is the main reference point for further studies of other
aspects. Such classification enables the identification of potential fish culture based on its
main characteristics. Such characteristics are well described by this new classification,
covering most of the cases. The Axial 1 tanks are the only tank type, which due to their
variability in tank size, seasonality and location are not clearly defined by such
classification.
52
Other constraints found, is the location variability of the radial tanks within the cascade
system. Although most of them are located at the top of the cascade system, a series of
radial tanks also appear close to the Axial 2 and 3 tanks, which are at the bottom of the
cascade. Either way radial tanks are situated on the outskirts of the cascade system.
New tanks keep being discovered on nearly a daily basis. These tanks mostly fit on the
new classification but as new ones are discovered, the variability characteristics
increases, therefore although the classification accurately describes known tanks a review
will be needed in the future.
The data on which the new classification is based on, although it gives an acceptable
description of tanks characteristics, can be criticized for the use of not very accurate
methods in terms of water spread and tank size measurements.
4.2 Biological aspects An assessment of the biological resources was critical since the output of the intended
development is directly related to this. These aspects are also limiting factors that need to
be taken into account in order to succeed.
4.2.1 Capture Fisheries
During the course of the last 50 years new species have been introduced into the Sri
Lankan reservoirs, species which are presently well established. Although some
restocking programs have been done in the study area, the majority of the fish population
is breeds and recruit naturally.
Production assessment reveals generally good fish production obtained mainly from
collective harvest obtaining an average of 50 kg/ha annually (Figure 9). Looking more
closely radial tanks; although being small and mostly highly seasonal, have better
production (kg/ha) than perennial tanks such as axial 3, even though the results were
observed in a drought year.
53
In terms of the fish caught the predominant species are tilapia species (around 50% of all
species) [Figure 10]. These species together with snakehead and small indigenous species
(SIS), are commonly found in most of the tanks are a part of the villagers diet.
It has to be pointed out that the involvement of man in the success of these species
survival and spread is minimal, which shows a big potential if fish culture is put in
practice.
4.2.2. Macrophytes
The presence of aquatic plants in the tanks is a factor that cannot be ignored since on
average 50% of the tank water surface is covered by macrophytes (Figure 15). The main
species present in most of the tanks are Nelumbo nucifera (Figure 15) and Nymphacea
lotus (Figure 16), which do not represent major disturbance for fishing and are source of
food for fish. The introduced noxious Salvinia (Figure 11), although it has heavy negative
impacts on the fishery and its culture, is only present in small amounts and in few tanks,
mostly perennial. Its presence appears to be mainly related to fishing activity, which is
greater in these tanks with the salvinia being spread mainly via fishing nets.
Other macrophytes are submerged plants, which although very abundant in most tanks,
their real abundance has not been properly assessed in this study, mainly due to the
difficulty in locating them in deeper parts of the tank during data collection; further study
of such plants is required. Their quick recovery and spread represent a problem mainly
for bathing activities in littoral areas.
In terms of abundance in the different tanks, the radial and the axial 1 tanks have the
lowest encroachment, below 40% (Figure16), and having as main species Nelumbo
nucifera, Nymphacea lotus and emergent grasses, making these tanks partially free of
macrophyte infestation problems.
Although a slight relationship between encroachment and fish production is appreciated
(Figure 17, 18), no conclusive results have been obtained. The low macrophyte presence
and high production in radial tanks could be an indication for such relationship, but
further analysis is required to test the hypothesis.
54
A more exhaustive study is recommended, using a more accurate system to estimate the
total tank area covered by macrophytes, plus a more detailed description of aquatic plants
present in such tanks.
An effective method to control macrophyte infestation is tank rehabilitation, which keeps
the tanks clear of macrophytes (<31% encroachment) for at least 3 years (Figure 19). Of
course, the rehabilitation process also affects the fish habitat, but such relationships have
not been looked at in this study due to insufficient data. Apart from desilting, carried out
in a few tanks, regular manual removal is practice only around bathing areas and some
fishing spots. Other control methods such as use of chemicals seems to be economically
non-viable specially for poor communities, unless provide by the government. The use of
bio-controls such as grass carp, water buffalo, beetles, etc, could be put into practice as in
other countries good results have been obtained (Gupta, 1987), but further research is
needed, to establish possible impacts.
4.3 Social-economic aspects
Poverty is an aspect, which seems to be related to the tank position within the cascade
system and to their seasonality. As population grows and space availability is reduced
people tend to be push towards the upper watersheds, which have less resources than the
bottom ones.
People at the bottom watershed tend to depend more in agriculture and the ownership of
land for other uses is bigger (Figure 21). This characteristic gives a more stable economic
situation. Those people at the radial and axial 1 tanks seem to rely more on natural
resources like hunting, illegal activities, fishing, poaching, etc. due to their lack of land
ownership.
Temporary labour, is more important in communities in the watershed among more
seasonal tanks (Figure 22). For instance at axial 1a 20% of the population relies on such
temporary labour, perhaps due to the high seasonality of these tanks which dry out
entirely every year requiring villagers to look for alternatives. On the other hand, because
radial tanks are not that highly seasonal more work is available within their own village.
At perennial tanks (A2, A3) the dependence on temporary labour is quite low, since they
have plenty of resources and land to exploit.
55
Another indicator of wealth is the housing (figure 23). In the study area the abundance of
temporary houses increases towards the more seasonal tanks and normally higher in the
cascade. At the axial 1a tanks the abundance of permanent houses (67%) could be due to
the great amount of f-farm labour which bring labour money from other villagers.
In Sri Lanka an ancient social division define a series of social groups or caste. Caste
which are closely related to wealth, although nowadays such traditional division is losing
in strength, still the differences can be appreciated. Typically higher caste peopleare
wealthier than those from lower castes.
Lower castes are present in higher numbers in radial tanks, where in axial 2 and 3 tanks
the majority of the caste are gobis (farmers). Although the relationship between caste and
wealth does not always apply, the distribution of lower castes towards radial and axial 1a
tanks is significant (Figure 24).
4.4 Conclusions
Seasonal tanks at the study area have a great potential for aquaculture. Although they do
not have the water availability that perennial tanks have, the knowledge about its water
availability cycle will allow to plan precisely the culture of fish in a sustainable manner.
The natural fisheries production of seasonal tanks is acceptable and not lower (kg/ha)
than in the less seasonal, supporting common fish species, which is part of the current
people’s diet.
Possible constraints like macrophytes infestation has been probed to be minimal
compared to the perennial tanks. Also social constraints are fewer than in the other tanks
due to their economic position, which makes them more open towards new strategies
such as fish culture.
Acceptable bio-physical conditions plus less possibilities of social constrains makes the
seasonal tanks a potential target for fish culture, but still the big issue in the study area are
the villagers priorities, where fisheries is at the bottom of the list and irrigation and
bathing are by far the main priorities. Priorities, which are believed by the villagers to be
affected if fishing, take place. Therefore the main impediment for the aquaculture
development success are the social aspects which still have strong traditional values.
56
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Abeywickrema, B.A, 1955. The origin and affinities of the flora of Ceylon Proc. Ceylon Asso. Advmt. Sci., Part 2: 1-23. Amarasinge U.S, 1985. Studies on the exploitation of minor cyprinids in Parakrama Samudra, a man made lake in Sri Lanka, using gill-nets. Journal of national Aquatic Resources Agency. Amarasinge U.S, 1990. Minor cyprinids resources in a man-made lake in Sri Lanka: a potential supplementary source of income for fishermen. Fisheries Research: 81-89. Amarasinge U.S, 1994. A synthesis on the management of the capture fisheries of Sri Lanka perennial reservoir Vidyodaya. Journal of Science, 5 (1). pp23-40. Chandrasena J.P.N.R. An illustrated manual of rice-field weeds in Sri Lanka. Publication #19. Department of Botany, University of Colombo, Sri Lanka. pp22-25 DAS 1996. Tabulated data presented by Wayamba Development Authority, Kurunegala, Sri Lanka. pp 30-31 De Silva S.S, 1983. Reproductive strategies of some major fish species in Parakama Samura reservoir and their possible impact on the ecosystem- a theoretical consideration. In: Limnology of Parakrama samura (F. Schiemer ed) pp183-191. W. Junk publishers. The Hague. Netherlands. De Silva, S.S and Sirisena H.K.G, 1987. New fish resources of reservoirs in Sri Lanka: feasibility of introduction of a subsidiary gill-net fishery for minor cyprinids. Fisheries Research. 6. 17-34. De Silva, S.S., 1988. Reservoirs of Sri Lanka and their Fisher ies. FAO Fish. Technical Paper (298):128p. De Silva, S.S, 1996. The Asian inland fishery with special reference to reservoir fisheries. A reappraisal. In: Perspective in Tropical Limnology (F. Schiemer and K.T. Boland (eds). Pp 321-332. Academic Publishing bv. Amsterdam, The Netherlands. De Silva, W. Indralal, 1997. Population Projections for Sri Lanka:1991-2041. Institute of policy studies. Colombo. Sri Lanka. pp 51-56 Edward, P. Food potential of Aquatic Macrophytes. 1980. Manila, Philippines, International center for Living Aquatic Resources Management. Fernando , C.H, & Indrasena, H.H.A, 1969. The freshwater fisheries of Ceylon. Bull. Fish. Res. Stn. Ceylon, 20:101-34.
57
Garaway C.J, 1995. Communal ponds in NE Thailand under different use-right systems:A participatory rural appraisal of their differing roles in peoples’ livelihoods. London (Imperial College) Gunawardena D. C. 1968. The flowering plants of Ceylon. An etymological and historical account of the flowering plants of Ceylon. Lake house investment LTD publishers. 1st edition. Gupta O.P. 1987. Aquatic weed management. A textbook an manual. 2nd edition. Today and Tomorrow printers and publishers. New Delhi. India. Hasnip N, Vincent L, Hussein K, 1999. Poverty reduction and irrigated agriculture. Rome, Italy, Food and Agriculture Organization of the United Nations. International Program for technology and research in irrigation and drainage. Itakura, J and Abernethy L. Charles, 1992. Water Management in a tank cascade irrigation systems in Sri Lanka. International irrigation management institute. Working Paper # 24. Colombo. Sri Lanka. Junk W. 1973. Aqautic weed in S.E. Asia. Procedings of a regioanl Seminar on Noxious Aquatic Vegetation, New Delhi. The Hague publishers. Pages 12-17. Kaufman, P. B. 1989. Plants: Their Biology and Importance. New York, NY: Harper and Row, Publishers. Miles, M. B, Huberman A.M, 1994. Qualitative Data Analysis. London, Sage Publications. Murray F.J, 1999. The Nature of small scale Farmer Managed Irrigation Systems in North West Province, Sri Lanka and the potential for Aquaculture. Stirling University. Aquaculture in Small-Scale Farmer Managed Irrigation Systems. Murray F.J, 1999. Summary of cultivation strategies and water management of sheds of Anamaduwa and Giribawa research. Stirling University. Aquaculture in Small-Scale Farmer Managed Irrigation Systems. Murray F.J, Koddithuwakku S & Little D, 2000. Fisheries Marketing Systems in Sri Lanka and the relevance to Development of the local Reservoir capture and culture-based Fisheries. Reservoir Fisheries Biology & Management. Stirling University. Aquaculture in Small-Scale Farmer Managed Irrigation Systems. Murray F.J, & Little D, 2000. The Lowland Dry Zone of Sri Lanka: Site for Study of Aquaculture Development in the humid Tropics and methodology for Participatory Situation Appraisal. Stirling University. Aquaculture in Small-Scale Farmer Managed Irrigation Systems.
58
NARA, 2000. Sri Lanka Fisheries Year Book (1999). Socio-economics and marketing Division, National Aquatic resources Research and development Agency, Colombo, Sri Lanka. Nathaniel, S, 2000. Integration of Aquaculture within irrigation systems; an overview of inland capture and culture fisheries in Sri Lanka with special reference to Mahaweli System H. Department for International Development. Working paper S-5. Newcastle. U.K. Niven C, Noble J, Forsyth S, Wheeler T, 1999. Sri Lanka. Lonely Planet publications. Seventh edition. Hawthorn, Australia. pp 10-16 Pemadasa, M.A, 1984. Grasslands in ecology and biogeography in Sri Lanka. Edited by C.H. Fernando. The Hague, The Netherlands, W. Junk Publishers, pp. 453-92. Perera, M.P, de Silva, M.B.G, 1997. Atlas of Sri Lanka. Arjuna Consulting Co Ltd. First edition. Sri Lanka. pp 23-27 Pet, J.S and Piet G.J, (1993). The consequences of habitat occupationand habitat overlap of the introduced Oreochromis mossambicus and indigenous fish species for fishery management in Sri Lanka reservoir. Journal of Fish Biology, 43 (Supplement A) 193-208. Penthiyagoda R, Rodrigo R. 1993. A revised handbook to the Flora of Ceylon. The wildlife Heritage Trust of Sri Lanka. Colombo. Sri Lanka. Pethiyagoda, R, 1999. Fishes in Trouble - the decline and fall of Sri Lanka’s freshwater fish fauna. Loris. 22 (2); 56-64. Piet G.T, 1996. Consequences of the eco-system perspective for the management of a tropical reservoir fishery. In: on the ecology of a tropical fish community (G.. Piet Ed.) pp 161-168. Thesis. Land bouwuniversiteit Wageningen. The Netherlands. Sakthivadivel, Nihal Fernando and Jeffrey D. Brewer, 1997. Rehabilitation planning for small Tanks in Cascades: A methodology based on rapid assessment. International Irrigation Management Institute. Research Report 13. Colombo, Sri Lanka. Smith, J.K, 2000. Conceptualising Conflict in Natural Resource Development Projects. University of Reading, Reading. Stern, K. R. 2000. Introductory Plant Biology. Toronto, Ont: McGraw-Hill.
59
Appendix 1. Average annual rainfall and temperature in Sri Lanka
(Source Perera et al 1997)
60
Appendix 2. Monsoon rainfall (Source Perera et al 1997)
61
Appendix 3. Sri Lanka Surface water (Perera et al 1997)
62
Appendix 4. Sri Lanka’s Population density distribution (Perera et al; 1997)
63
Appendix 5. Data Clearing Methodology
The following appendix describes the main methods used during the data clearing
process. This information refers to the cascade typologies data include in the attached
disc (Appendix )
1) Hydrology Spreadsheet
Maha yield (bush/ac, number/year)
Separation in two columns: a) bush/ac b) number/year
Units change: bush to Kg (1=22) and ac to ha (2,47 to 1)
Problems: Inconsistency in values ex. 75-85 bush/ac
Solution: use of a middle value. Ex. 80 bush/ac
Yala yield (same process applied as in Maha)
Type of crop has been delete since only 4 tanks had available information.
Tank access
CPR= Common property, T= Temple.
Catchment area
Regrouping and unit change: Group I: 0-10 ac (0-4,04 ha)
Group II: 10-50 ac (4,04-20,24 ha)
Group III: 50-100 ac (20,24-40,48 ha)
Group IV: 100-250 ac (40,48-101,21 ha)
Tank bed cultivation
RFP (top): change to “yes” group II
Paddy: change to “yes” group I
64
Command area
Units change: ac to ha (1:2,47)
Problems: Inaccurate data, ex. 20-25 ac.
Solution; use of middle value, ex. 22 ac
Maximum Depth, Maximum water spread, dead storage, Minimum residual waters,
Yala Spill Frequency, Maha spill frequency, to all the mentioned factors the same
Procedure as in the command area has been applied.
Maha Spill months
Grouping: Group I: November, Group II: December, Group III: Nov-Dec,
Group IV: Dec- January, Group V: Jan-Dec, Group VI Oct-Nov.
Yala Spill months:
Grouping: Group I: April, Group II: May, Group III: June, Group IV: Apr-May
Group V: May-June
Dry Frequency:
0.5 means 1 year out of 10 years, and 0.25 1 year out of 20.
Dry Months
Grouping: Group I: August, G II: July-Aug, GIII: Jul-Sept, G IV: Aug-Sept,
G V: June-July, G VI: Feb-March, G VII: Apr-May, G VIII: Jun-Sept
G X : July-Oct, G XI: March-May, GXII: Aug-Oct, G XIII March-Oct
G XIV: May-Sept, G V: June-Oct, G VI: March-Oct
Season Class
P(St) and P(HS), typing errors convert to P and HS
65
Cropping intensity
Some cells values given were unclear, ex: 0-25%, after consulting with the data entry
responsible, data was tidy to 25%.
Number of rains
Raw data ex: 2-3 R, was changed to Group I: 1-2 rains, Group II: 2-3 rains,
Group III: 3 rains.
Data with just FR and HF was place in Group I and II respectively.
Time for field preparation
Grouping: 1 week: Group I, 2 weeks: G II, 3 weeks: G III, 4 weeks: G IV,
1-2 weeks G V, 2-3 weeks G VI, 3-4 weeks: G VII.
Preparation: rain or stored water (number /year)
Separated in two columns a) number b) year
Rice variety (number/year)
Value 3.5 were round to 3 months since is the same type.
As before separation into two columns (number and year)
Variety, duration and synchronisation
Variety: Synchronise or not synchronise
Duration: Synchronise or not synchronise.
Grouping: Nadu: Group I, Samba: Group II, Nadu/Samba: Group III.
Release Numbers
If two values give, the mean value has been inserted.
In case of ex: 6-7 the higher number was taken (this method has been applied to all the
different cases in all the spreadsheet)
66
Unclear data, where values given refers to one season or the whole year, season, request
further research to clarified. Provisionally taken as year wise.
Release Synchronisation (days)
Separation into two columns, a) days and b) Synchronisation (yes or no)
2) Fisheries Spreadsheet
Priorities uses of water
New ranking given (1-5), Most important (1), less important (5)
Use or systems or tank for bathing.
New ranking 1-10, 10 more used, 0 no use at all.
Same ranking applied for other systems, tanks and livestock.
External Participants
Split in different columns, each column is a different tank. Those tanks where external
participation took place have been mark with a 1. The total number of participants has
been omitted.
Other external participants not included.
Pre Collective Fishing patterns
Split in 6 columns, gear type (4 different gears) and ownership type (2 types)
Period of time is been omitted.
Species quantity stocked
The Number is not very accurate.
Tanks fished by villagers
(Number of households participating at the village, score volume of fish.
67
Data split is three different columns: a) Number of tanks fished by villagers
b) Number of households involved
c) Rank in terms of amount of fishing time
Problems: Given 2 values ex: 3-4 households, the higher was chosen.
Socio-economic characteristics of self-consume fishermen
Split in 5 columns: landless, youth, farmers, coolie (temporal labour) and OFL.
Those tanks where the different characteristics took place were mark with a “1”.
Collective Fishing Harvest (Kg) by species.
Divided in different columns by species (two sections: percentage and Kg)
Inconsistency data, most of the Kg data missing has been worked out based on the
percentage.
Uses of Harvest
Division on 4 columns.
Coding 1:yes, 2:no.
In all the cases, where fishes species are used, is no clear whether the data collector made
a difference between Ori. Mossambicus and Ori. Nilotica.
Livestock spreadsheet
Local Sharecroppers under tank
Number of households, surnames and Acres (pass into hectares)
Due to the unavailability of surnames data with area information only number of
households has been used.
68
Appendix 6 : Macrophytes Taxonomic identification 1) Salvinia molesta (Salvinia or velvet weed)
Division: Polypodiophyta
Class: Polypodiopsida
SubClass: Salviniidae
Order: Salviniales
Family: Salviniaceae
A free floating sporophyte. Leaves in ternate whorls on horizontal rhizones; a pair of
leaves floating third one submersed, finally dissected to sporocarps. In Thinly populated
mats the floating leaves are flat oval to egg-shaped and about 1 cm wide. But in dense
mats the salvinia leaves are conduplicated folded up to 4 cm wide. Salvinia molesta
leaves are hairy tom provide buoyancy. Propagation largely by offsets; it’s asexual
reproduction is uncertain (Junk, 1973).
Mostly on stagnant or slow moving fresh-water, shallow or deep; ponds, lakes,
irrigation canals, watercourses, in swampy marshes or inundated rice-fields in wetter
regions. Often very abundant covering whole water surfaces (Penthiyagoda, 1993)
Figure 1 &2 (photo and drawing)
Figure 25. Salvinia molesta physiology by R,G, Howell. Figure 26. Salvinia molesta in the wild.
The popular belief is that this water fern was first introduce into Sri Lanka by a
botanist who had brought it for scientific study, and it is presumed that during a spell
69
of very heavy rain this plant had escaped with the overflowing water into the city
drainage net work. Due its rapid growth and multiplication it soon establishes in the
low-lying areas and waterways in the suburbs of Colombo. The re was general belief
that the British army had introduced this weed to camouflage the waterways around
Colombo ( Junk, 1973).
2) Pistia stratiotes (water lettuce)
Division: Magnoliophyta
Class: Liliopsida
SubClass: Arecidae
Order: Arales
Family: Araceae
Perennial, free floating herb, sometimes anchored to wet mud. Leaves tongue-shaped, in
shell like rosettes, up to 20mm wide puplpy with aerenchyma to hold the plant above the
water level light green in colour and covered with tiny hydrophobic trichomes.
Inflorecent a spandix with spathe in the hollows of the leave. Propagation by offsets buds
and seeds.
Introduced as an ornamental plant. It is a floating plant which normally grows in stagnant
water or slowly flowing water. Pistia is also able to grow in wet or marshy areas where
there is little water. Triman reports that is able to grow in somewhat brackish water near
the coast (Junk, 1973)
.
Figure 27. Pistia stratiotes by Murray A.
70
3) Echhornia crassipes (Water hyacinth)
Division: Magnoliophyta
Class: Liliopsida
SubClass: Liliidae
Order: Liliales
Family: Pontederiaceae
Floating or in shallow water rooting perennial plant with axiallary stolons, forming easily
detachable new plants at the ends. Stems densely covewred with petiole bases and roots
and numerous rootless. Leaves in rosette, thick, glossy green, broadly ovate, with
subcordate or rounded base and obtuse apex, 7-25 cm in diameter, glabrous; petiole
spongy, up to 30 cm in adult leave, gradually narrowed upwards. Flowers zygomorphic,
bisexual, in long –stalked, erect spikes, up to 50 cm long, bearing 18-35 flowers, bending
downwards after flowering; penducles with 2 bracts (spathes), tubular; perianth also
tubular; tube 15-18mm long base green, top pale green; lobes 6, mauve in colour, the
anterior one 3-4 cm long. Stamens 6, attached to perianth tube, the 3 anterior small, other
3 much longer. Ovary superior, 3-celled, multi-ovulate, axile placentation; style long,
slender; stigma hairy with 3 lobes; capsule membranous, 3-valved, surrounded by
persistent perianth. Seeds many, minute, ribbed, obovoid. It propagates by seeds and
plant fragments (figure xxx).
Introduce by man, mainly due to the belief among the people that the flowers of this
weed produce a mauve coloured dye, which could be used to counterfeit currency notes.
Another misconception about this plant is related to its suppose ‘ayurvedic medicine’.
Many times people have made efforts to grow it in private pools and ponds. The plant
actually used in medicine in not the water hyacinth but Monochoria hastada (Diya-
habarala).
71
Figure 28. Eichhornia crassipes Figure 29. Eichhornia crassipes by IFA .
4) Nelumbo nucifera (Nelum or sacred lotus)
Division: Magnoliophyta
Class: Magnoliopsida
Family: Nelumbonaceae
Perennial water plant. Leaves peltate or orbicular, 60-90 cm wide without any slit.
Flowers elegant white-pin, sweetly scented, prominently emerged on long stalks. Fruits
spongy, flat-topped 10-15 cm in diameter. Propagation by seeds and farinaceous, long
fleshy edible rhizomes.
Figure 30. Nelumbo nucifera by Fagg, M Figure 31. Nelumbo nucifera at the tank
72
5) Ceratophyllum demersum ( Veru,Coontail / Hornwort) Division Magnoliophyta Class Magnoliopsida, the Dicotyledons Subclass Magnoliidae Order Nymphaeales Family Ceratophyllaceae. Genus Ceratophyllum. Description: Free floating or attached to sediment, stems
branched and often up to 1 m long. Coarse, weakly and irregularly toothed compound
leaves (2/5"- 1 3/5" long) retain their shape when removed from the water.
Flowers: Small purple clusters (rarely)
Because its feathery leaves are arranged in whorls on the stem, this plant resembles a
racoon's tail. The fan-shaped leaves are best observed in the water. They look feathery
because each leaf is divided into many narrow segments. Each leaf has several small
teeth on the midribs. These tiny teeth give the plant a rough feel when pulled through the
hand. Coontail's flowers are very small and rarely seen.
Figure 32. Ceratophyllum demersum Figure 33. Ceratophyllum demersum leaves
73
6) Eleocharis dulcis (Water chestnut) Phyllum: Angiospermae Class: Moncotyledonae Order: Cyperalis Family: Cyperaceae This plant has stolons and tubers. Its culms are robust, transversely septate of 50-100
cm tall. Leave blade reduced with purplish sheath, 10-20 cm long. Inflorescence with
single spike, terminal, cylindrical 1.5-3.0 cm long. Spikelets sessile round 2-5 cm long.
Perennial sedge and propagated by stolon, tubers and seeds. An apical bud emerged
from the tubers and then swallon to form a basal bulb(corm) usually at the soil surface.
Arial shoot and root will grow from the germinated tuber. Branches of rhizomes will
eventually form an extensive network underground. These rhizomes usually domiant in
undisturbed areas but the dormancy break when they are disturb or break in fragment
during ploughing. This indicate that ploughing initiate the growth of this weed.
This sedge are found in aquatic conditions such as rice fields, swamp and waste lands.
Figure 34. Eleocharis dulcis 7) Nymphoides indica Division: Magnoliophyta Class: Magnoliopsida Subclass: Asteridae Order: Solanales Family: Menyanthaceae
74
Genus : Nymphoides Flower Shape: Stellate Flower Color: White Flower Size: 1" Leaf Shape: Ovate to circular Leaf Coloration: Green Leaf Size: To 12" Leaf Spread: To several feet This is by far the largest of the Nymphoides. Its leaves can grow to 12"
in diameter a and its flowers are larger, have more petals, and are fringed,
instead of being plainly edged. Its flowers are produced from
beneath the leaf, as with N. cristata. These flowers have 7-9 petals,
though, instead of the standard 5. As the season winds down, the plants
reduce to tuber clusters and most of the original stems die off, allowing
the offspring to drift away to their fates.
Figure 35. Nymphoides indica photo Figure 36. Nymphoides indica drawing
75
8) Utricularia vulgaris (Bladderwort) Family: Lentibulariaceae Distribution: Fresh waters, usually found in ponds and reserviors, but ca also exist in
slow moving tidal areas.
Description: Very fine, much branched plant with numerous bristle -like alternate leaves 1
to 2 cm long and 0.5 mm wide. re rootless. They have main stems from which lacy, often
complex leaves grow. Bladderwort flowers are usually bright yellow the flowers have
two "lip-like" petals of about equal size. Flowers are on long stalks that emerge several
inches above the water. The carnivorous bladders are attached at regular intervals along
the linear leaf segments.
Reproduction: By seed
Figure 37. Utricularia vulgaris at the tank
Figure 38. Utricularia vulgaris physiology
76
Appendix 8. Statistical analysis results
Table 7. Chi square test results from water input and seasonality data. Significance values below 0.05 are significant.
Table 8. Chi-square test results from maximum water spread and water availability. Significance values below 0.05 are significant.
Table 9. Analysis of variance (Univariate) test results from the annual fisheries production. Significance values below 0.05 are significant.
Chi-Square Tests
81.964a 12 .00083.517 12 .000
16.132 1 .000
91
Pearson Chi-SquareLikelihood RatioLinear-by-LinearAssociationN of Valid Cases
Value dfAsymp. Sig.
(2-sided)
15 cells (75.0%) have expected count less than 5. Theminimum expected count is .40.
a.
Chi-Square Tests
84.969a 9 .00095.176 9 .000
30.219 1 .000
91
Pearson Chi-SquareLikelihood RatioLinear-by-LinearAssociationN of Valid Cases
Value dfAsymp. Sig.
(2-sided)
9 cells (56.3%) have expected count less than 5. Theminimum expected count is 1.33.
a.
Tests of Between-Subjects Effects
Dependent Variable: PRODUCTI
279338.710a 8 34917.339 4.506 .00066608.722 1 66608.722 8.595 .00569306.321 1 69306.321 8.943 .004
112246.188 4 28061.547 3.621 .01161919.543 3 20639.848 2.663 .058
395219.396 51 7749.400836512.232 60674558.106 59
SourceCorrected ModelInterceptTANK_TYPFISHITYPTANK_TYP * FISHITYPErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .414 (Adjusted R Squared = .322)a.
77
Table 10. Analysis of variance (Univariate) test results from fish species distribution. Significant values below 0.05 are significant.
Table 11. Analysis of Variance (Univariate) test results from tank macrophytes distribution Significant values below 0.05 are significant.
Table 12. Analysis of Variance (Univariate) test results from macrophytes distribution at the different tanks. Significance values below 0.05 are significant.
Tests of Between-Subjects Effects
Dependent Variable: CATCHTRA
8.590a 15 .573 6.506 .00015.388 1 15.388 174.819 .000
3.898E-02 3 1.299E-02 .148 .9317.389 3 2.463 27.984 .000
.561 9 6.237E-02 .709 .7007.746 88 8.802E-02
34.809 10416.336 103
SourceCorrected ModelInterceptTANKTIPOFISHSPECTANKTIPO * FISHSPECErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .526 (Adjusted R Squared = .445)a.
Tests of Between-Subjects Effects
Dependent Variable: ENCROACH
13.427a 4 3.357 67.587 .00012.121 1 12.121 244.068 .00013.427 4 3.357 67.587 .00022.001 443 4.966E-0247.505 44835.428 447
SourceCorrected ModelInterceptSPECIESErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .379 (Adjusted R Squared = .373)a.
Tests of Between-Subjects Effects
Dependent Variable: SURFCOV
16.206a 24 .675 14.243 .00010.571 1 10.571 222.993 .00010.472 4 2.618 55.222 .000
.907 4 .227 4.782 .0011.489 16 9.304E-02 1.962 .015
16.498 348 4.741E-0245.405 37332.704 372
SourceCorrected ModelInterceptESPECIESTANKTYPESPECIES * TANKTYPErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .496 (Adjusted R Squared = .461)a.
78
Table 13. Chi-squares test results from desiltation impacts. Significance values below 0.05 are significant
Table 14. Analysis of Variance (Univariate) test results from distance to infrastructures from the different tanks.
Table 15. Analysis of variance (Multivariate) test results from ownership distribution. Significance values below 0.05 are significant.
Chi-Square Tests
13.847a 4 .00815.398 4 .004
7.940 1 .005
76
Pearson Chi-SquareLikelihood RatioLinear-by-LinearAssociationN of Valid Cases
Value dfAsymp. Sig.
(2-sided)
4 cells (44.4%) have expected count less than 5. Theminimum expected count is 1.79.
a.
Tests of Between-Subjects Effects
Dependent Variable: DISTANCE
432.683a 19 22.773 5.529 .000875.694 1 875.694 212.609 .000253.070 3 84.357 20.481 .000
9.019 4 2.255 .547 .70139.490 12 3.291 .799 .650
362.454 88 4.1191913.250 108
795.137 107
SourceCorrected ModelInterceptINFRAESTTANKTPINFRAEST * TANKTPErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .544 (Adjusted R Squared = .446)a.
Multivariate Testsc
.842 29.302a 2.000 11.000 .000
.158 29.302a 2.000 11.000 .0005.328 29.302a 2.000 11.000 .0005.328 29.302a 2.000 11.000 .000.928 3.463 6.000 24.000 .013
.262 3.503a 6.000 22.000 .0142.098 3.497 6.000 20.000 .0161.663 6.651b 3.000 12.000 .007
Pillai's TraceWilks' LambdaHotelling's TraceRoy's Largest Root
Pillai's TraceWilks' LambdaHotelling's TraceRoy's Largest Root
EffectIntercept
TANKTYPE
Value F Hypothesis df Error df Sig.
Exact statistica.
The statistic is an upper bound on F that yields a lower bound on the significance level.b.
Design: Intercept+TANKTYPEc.
79
Table 16. Analysis of Variance (Univariate) test results form coolie labour at the tanks. Significant values below 0.05 are significant
Table 17. Analysis of variance (Univariate) tests results from housing characteristics Significant values below 0.05 are significant.
Table 18. Analysis of variance (Univariate) test results from caste and watershed relationship. Significance values below 0.05 are significant.
Tests of Between-Subjects Effects
Dependent Variable: COOLIE
298.725a 4 74.681 3.439 .033460.313 1 460.313 21.196 .000298.725 4 74.681 3.439 .033347.473 16 21.717
1000.440 21646.198 20
SourceCorrected ModelInterceptTNKTYPErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .462 (Adjusted R Squared = .328)a.
Tests of Between-Subjects Effects
Dependent Variable: NUMBERS
27406.935a 14 1957.638 2.411 .00922969.419 1 22969.419 28.288 .000
9648.808 4 2412.202 2.971 .0265841.888 2 2920.944 3.597 .0336027.954 8 753.494 .928 .500
53591.016 66 811.985123755.000 81
80997.951 80
SourceCorrected ModelInterceptTANKTIPHOUSETYPTANKTIP * HOUSETYPErrorTotalCorrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .338 (Adjusted R Squared = .198)a.
Tests of Between-Subjects Effects
Dependent Variable: TANK#
18215.050a 23 791.959 42.165 .00026373.066 1 26373.066 1404.135 .000
527.134 4 131.784 7.016 .00012122.417 6 2020.403 107.569 .000
3039.562 13 233.812 12.448 .000
694.950 37 18.78277531.000 61
18910.000 60
SourceCorrected ModelIntercept
TANKTYPCASTE
TANKTYP * CASTEErrorTotal
Corrected Total
Type III Sumof Squares df Mean Square F Sig.
R Squared = .963 (Adjusted R Squared = .940)a.
80