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MODELING FOR SUITABLE SITE SELECTION FOR SHRIMP _Penaeus monodon

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MODELING FOR SUITABLE SITE SELECTION FOR SHRIMP _Penaeus monodon Powered By Docstoc
					Paper presented at GIS’2000, Toronto, Canada, on 13-16 March’2000

Optimizing sites selection for development of shrimp (Penaeus monodon) and mud
crab (Scylla serrata) culture in Southwestern Bangladesh.

*Salam, M. Abdus, Lecturer, Department of Aquaculture, Faculty of Fisheries,
Bangladesh Agricultural University, Mymensingh- Bangladesh. Phone: +88 091 55695-
7/2525, E-mail: m.a.salam@stir.ac.uk

**Ross,L. G, Professor, Institute of Aquaculture, University of Stirling, Stirling FK9
4LA, Scotland, U.K., Phone: +44 1786 466594, Fax : +44 1786 472133; E-mail:
lgr1@stir.ac.uk

Abstract

A comparative study was carried out for selection of suitable sites for shrimp and mud
crab culture using remote sensing and GIS as a tool. Landsat TM images of 1996
covering the southwestern part of Bangladesh were used as the primary data source.
Image analysis was used to identify water bodies, the extent of brackish water and
associated land use features in the image. Digitizing secondary data from different
sources, including hard copy maps supported remote sensing. A GIS database was built
up while incorporated environmental layers such as water bodies, rivers, soils, land use,
water temperature, rain fall, salinity and pH. The study also included infrastructural
issues, such as roads, railways, shrimp and crab marketing and processing plants, towns
and cities. A series of GIS models were developed based on biological databases for key
species, current farming systems and practice. The most suitable sites for shrimp and crab
farming in the area were identified. GIS modeling associated with remote sensing have
great potential for informed decision-making in aquatic production systems. The
implications for use of these systems in reducing land use conflict are discussed.

Introduction

World aquaculture production in 1995 reached 112.3 million tons (FAO, 1997) and has
great potential for further expansion especially in certain sectors. This is particularly so
because of the declining capture fisheries having in the past decade. However,
aquaculture activities have also created environmental impact in developing countries, for
example, shrimp culture has destroyed mangrove ecosystems in most countries of south-
east Asia (Menasveta, 1997). To overcome these problems while maximizing aquaculture
production, needs comprehensive development planning based on the evaluation of
water, land and human resources and interpretation of environmental and socio-economic
constraints (Kapetsky, 1988). Therefore, there is a need for an approach, which can be
used to rapidly identify areas of a country, a state or smaller units, suitable for various
aquaculture activities as an aid to development planning.

Aquaculture development potential can be assessed synoptically using Geographical
Information Systems (GIS). A GIS is a computer-based tool for mapping and analyzing



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things that exist and events that happen on earth. GIS technology integrates common
database operations such as query and statistical analysis with the unique visualization
and geographic analysis benefits offered by maps. These abilities distinguish GIS from
other information systems and make it valuable to a wide range of public and private
enterprises for explaining events, predicting outcomes, and strategies (ESRI, 1998).

GIS has begun to be applied in aquaculture relatively recently. A number of studies using
GIS technologies have been published (Table 1). Most of the works have covered large
geographical areas, dealing with regions, state or even entire country and have been
principally concerned with aquaculture planning (Manjarrez and Ross, 1995).

This paper presents the results of application of Remote Sensing and GIS techniques to
estimate the area available for aquaculture development and to assess site suitability in
the Khulna region of Bangladesh for aquaculture of the mud crab (Scylla serrata) and the
giant tiger shrimp (Penaeus monodon). In addition to this, the models are used to estimate
the production potential and economic returns from these activities in the study area.

Table 1. GIS studies in the field of Fisheries and Aquaculture during 1987 to 1999
Region/      Resolution    Aim of work                      Culture species              Author(s)     Date
Country
U. K         10kmx10km     Siting trout farms               Oncorhynchus mykiss          Meaden        1987
Costa Rica   -           Regional site selection for        oyster, mussel,              Kapetsky      1987
                         oyster, mussel, clam, shrimp       clam and shrimp
USA          -           Regional suitable site for         Channel catfish              Kapetsky      1988
                         channel catfish                    Ictalurus punctatus
Pakistan     75km x 75km Siting carp farms                  Major carps                  Ali et al.    1989

Malaysia     -             Regional suitability of          Fish and shrimp              Kapetsky      1989
                           fish and shrimp
USA                        Regional catfish and craw        Catfish, I. Punctatus and    Kapetsky      1990
             -             fish potential assessment        Crawfish, Procmbarus
                                                            clarkii
Chile                      Salmon and mussels               Salmonids and mussels        Krieger &     1990
             -             cage, pen and bed culture                                     Muslow
Norway       -             Siting Salmon and                Salmon and rainbow           Ibrekk et al. 1993
                           rainbow trout farms              trout
U. K         25m x 25m   Sites for salmon cage culture      Salmonids                    Ross et al.   1993
             10m x 10m
Africa       18km x 18km Warm water fish culture in         Fish culture, O. niloticus   Kapetsky      1994
                         African continent                  And Clarias gariepinus
Vietnam      -           Potential for rice-fish and fish   Prawn and fish               Thu and       1996
                         culture                                                         Demaine
Mexico       250m x 250m Regional aquaculture model for     Shrimp, P. vannnmei          Manjarrez     1996
                         shrimp culture
Canada       1.1km x     Regional suitable site for         Mussels, oyster,             Habbane et 1997
             1.1km       mussels, oyster, salmon and        salmon and lobster           al
                         lobster




                                                                                                       2
Latin        -           Continental assessment for     tilapia, carp and          Kapetsky    1997
America                   tilapia, carp and tambaqui   tambaqui pacu culture       and Nath
                         pacu culture
Thailand     -           Site suitability for shrimp   Shrimp, P. monodon          Jarayabhand 1997
                         culture
Africa       5km x 5km   Continental assessment for                                Manjarrez   1998
                         warm water fish culture of    Tilapia, catfish and carp
                         tilapia, catfish and carp
Bangladesh   30m x 30m   Suitable site for brackish    Carps and freshwater        Salam and   1999
                         water shrimp & freshwater     Prawn, M. rosenbergii &     Ross
                         prawn and fish culture        Shrimp, P. monodon

Materials and Methods

Study area

The study area is situated in the Sub-tropical southwest end of Bangladesh, between
latitudes 210 50’ and 24015’ North and 89000’ and 90005’ East longitudes (Figure1). It is
bounded in the north by Rajshahi division, northeast by Dhaka, southeast by Chittagong,
south by Bay of Bengal and west by India. It encloses a ground surface area of
14,000km2 comprising of 6 major district towns namely Khulna, Jessore, Satkhira,
Narail, Gopalganj and Bagerhat. The area contains an International Sea port at Mongla in
Bagerhat, one inland port and one regional airport in Jessore. This area is one of the most
promising for aquaculture due to the presence of the largest continuous mangrove forest
the Sundarbans (Viju, 1995), which act as a transitional zone between the fresh and
brackish water.




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Figure1: Map showing the study area, Khulna, Jessore, Satkhira, Narail, Gopalganj,
        Bagerhat and the Sundarbans Mangrove forest.
Aquaculture practiced in the area

The southwestern coastal region of Bangladesh is one of the most promising areas for
aquaculture due to two major factors. Firstly, its fresh and coastal water resources are the
most abundant in the country. Secondly, the world’s largest continuous mangrove forest
is situated in the region, which provides a food source and nursery for the offshore
fishery, protection of the coasts from storm surges and cyclones, domestic and
commercial products, recreation and tourist services, habitat for shrimp, fish and other
crustaceans cultivation. Culture of fresh and marine water fish, shrimp and crab are
highly important as they can be easily integrated with other activities such as agriculture
and livestock rearing.

Traditional fish and shrimp aquaculture along the intertidal zones of the Bangladesh
coastal area is an age-old practice. In some areas of Khulna, Satkhira and Bagerhat,
bordering the tidal river system, shrimp (Penaeus monodon) and fish post larvae are
trapped and allowed to grow to marketable size and harvested 3-4 times in a growing
season. This practice has gained considerable momentum in the last decade because of
high demand for shrimp in the international market. Farmers have abandoned their rice
fields and started growing shrimp because the economic return from shrimp is higher
than the rice cultivation (Shahid, 1992). Khulna region has around 104,624 ha of shrimp
farm in production (DOF, 1994-95), which are more than 60% of total shrimp farm in the
country. The artisanal fishermen from the rivers and their tributaries in the region also
harvest shrimp.

Mud crab (Scylla serrata) commonly known as “mangrove crab” has been an incidental
product of culture operations meant to raise milk fish, prawn and other fin fishes, in
Southeast Asian Countries (Chandrasekaran and Perumal, 1993). There are three families
and seven species of commercial crabs available in the Sundarbans water and mangrove
floor. Four hundred million kg of fiddler crabs and 100 million kg of mud crabs were
harvested in 1991 form the Sundarbans ((Ali, 1998). In the past farmers offered them to
their shrimp as food. Due to religious preference and the food habits of the country, there
was no potential use of the crab but with the fall of shrimp price in the international market,
farmers have incurred heavy losses (Khulna correspondent, 1999). Disease outbreaks in the
shrimp ponds in 1994, made farmers shift from shrimp culture to crab culture as crab gained
importance for export in the international market.

Software used

The GIS software used in this study was IDRISI for Windows version 2.0; a raster based
GIS, developed at Clark University, USA. TOSCA digitizing system (Version 2.03),
DIGI-EDIT (Version 1.050), Paint Shop Pro-5 and Microsoft Paint for image editing and
CalComp Drawing Board III were used to digitize maps and edit vector layers. The
software operated on a Pentium Pro 200 MHz processor with 128Mb RAM, 10 Gb hard




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disk. Display was via an iiyama Vision MasterTM 21” colour monitor using a Matrox
Millennium 8Gb video card.
Remotely sensed data sources

The primary data sources for this study were two adjacent Landsat TM satellite images
containing three multi-spectral bands (2, 3 and 4), acquired on 9 and 16 February 1996. A
cloud free area of (column 3676 by 4915 rows) 18067540 pixels was subset from the
original two full scene image using WINDOW module in IDRISI. This sub-scene image
was geometrically rectified to the Lat/Long grid co-ordinate system using 139 reference
points on the 1:50, 000-scale map. The rectification was achieved at an accuracy of 8.7m.

Thematic maps

Data were extracted from a range of sources. Soil texture and soil pH was extracted from
soil reconnaissance survey maps prepared by the Soil Resources Development Institute
(SRDI) during the period of 1972 to 1975. Land use, flood, storm surge and drought were
taken from SRDI maps of 1997. Soil and water salinity was taken from SRDI soil
salinity report 1997 and Surface Water Modeling Center (SWMC) report 1996. Roads,
railways, rivers, international boundary and other topographical information were taken
from topographical maps produced by Survey Bangladesh, scale 1:50,000, prepared
during 1972-1979. Population density, agricultural by-product, animal waste were taken
from Bangladesh Bureau of Statistics (BBS) 1996 and BBS pocket dictionary 1996.
Other data were taken from different sources such as atlas, journals, periodicals and
published papers.

Database development

The data collected from various sources and in different forms were converted to
thematic layers of the GIS by using one of the following methods:
I.     Scanning and editing maps
II.    Digitizing maps using a digitizer board
III.   Digitizing maps using on screen facilities
IV.    Transforming tabular data in to vector or raster format
V.     Classifying remotely sensed images

Construction of Sub-model

In order to determine potential sites for brackish water shrimp and crab farming, thirty-
five physical, environmental and socio-economic criteria were selected and compiled.
Suitability ratings for each criterion were employed, and each factor was reclassified into
a suitability layer scored on a 1 to 4 ranges used by Kapetsky and Nath (1997), very
suitable = 4, suitable = 3, moderately suitable = 2 and currently not suitable = 1. Table 2
summarizes the reclassification criteria adopted in this study.

Water sources: Water can be compiled from thematic data on irrigation schemes,
rainfall runoff, and river channels and from groundwater sources. For this study, an



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indication of water availability for brackish water shrimp and crab culture was assessed
by constructing a layer based on perennial streams, tidal canals and river channels from
remotely sensed Landsat image.

Water chemistry: The water chemistry sub-model was prepared from different sources
of thematic layer and tabular data. Water temperature was calculated from air
temperature using a regression equation (Kapetsky, 1994) and likewise, dissolved oxygen
was derived from temperature and salinity relationship describe by (Colt, 1984). Water
salinity was taken from SWMC report (1996) and data on water pH collected during a
field visit (1998), were also used to develop the water chemistry sub-model.

Available Land: All land in various categories, which would not be available for
development was removed from consideration, such as rivers, roads, reserve mangrove
forest and urban development. The land, which was considered most suitable for this
study, was that which is not intensively used for agriculture, in order to minimize the
conflict with other activities. This layer was created by classifying Landsat images.

Soil chemistry: Soil quality was also an important land criterion. From the soil
reconnaissance map of SRDI during the period of 1972 to 1975, a soil texture and pH
layer were created by digitizing the map and converted into raster format. Soils were
classified according to their texture (Figure 2, Coche, 1985). Data on salinity and pH
collected during a 1998 field visit were also used to develop the soil chemistry sub-
model.




Figure 2: Comparison of the best soils for shrimp and crab pond construction with



                                                                                           6
          the soil texture classes (modified after Coche, 1985)
Infrastructure: Infrastructure was considered as an important criterion for the
development of shrimp and crab culture. Therefore, roads were extracted by digitizing
from the map 1:50,000 scale of Survey Bangladesh and also from Landsat TM image.
This sub-model also included distance from processing plants, markets and fish seed
sources from nature and hatchery.

Inputs: The availability of waste from cattle and poultry manure and agricultural by
products such as rice and wheat bran was considered as inputs. These were taken together
to determine whether sufficient inputs were available to support shrimp and crab farming
at a prescribed minimum level. The spatial distribution of the combination of these inputs
was mapped from the tabular data of BBS (1996).

Support: A layer was compiled for support from Non Governmental Organizations
(NGO) using tabular data. The support sub-model also contained Government offices,
Research stations, Universities and agglomeration, which were computed from maps and
tabular data.

Risk assessment sub-model: To compile the risk sub-model, different factors such as
winter rainfall, pollution from the industries and town center, drought and elevation were
added together from maps and tabular data.

Natural indicator: Proximity to mangrove forest generally means good water quality,
availability of fish and crustacean fry and food for all sorts of aquatic animals (Ali,
1998). This layer was extracted from Landsat image classification.

Constraints:

Available data shows that 48.7 per cent of the land is available for culture practice in the
region (Khan, 1998). The rest of the land is either already used by the permanent
structures or restricted by law for any development activities. These areas are the
mangrove forests, the rivers, canals, floodplains and other wet lands, which are
unavailable because they are used by hundreds of thousands of fishes, crustaceans,
zooplankton and phytoplankton for their feeding, breeding and migration purposes.
Moreover, the roads, towns, ports and villages, which have permanent structures, are also
not available for use (Manjarrez, 1996). Figure 3 shows the conservation areas in the
region.




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Figure 3. Constraints for aquaculture and other activities

Table 2. Classification scheme carried out in the study modified from Kapetsky and
         Nath, 1997

                                  4               3               2               1
Factors                     Very suitable    Moderately       Marginally      Presently
                                              suitable         Suitable       Unsuitable
Water parameters
Water temperature for         22-300C       18-22, 30-330C   15-18, 33-350C   <15 >350C
shrimp and crab
Salinity for shrimp and       8-26ppt       5-8, 26-32ppt     4-5, 32-37ppt   <4 >37ppt
crab
Dissolved oxygen              5-10ppm       4-5, 10-12ppm    3-4, 12-13ppm    <3 >13ppm
Water pH                       6.5-8.5          5.5-6.5          4.5-5.5       <4.5 >8.5
Support
Distance to NGO’s             <5,000m       5,000-10,000m    10,000-15,000m   >15,000m
Distance to Govt. offices     <3,000m        3,000-5,000m     5,000-10,000m   >10,000m
Agglomeration                 <1,000m        1,000-2,000m     2,000-3,000m    >3,000m
Distance to Research          <5,000m       5,000-10,000m    10,000-15,000m   >15,000m
stations
Distance to Universities      <5,000m       5,000-10,000m    10,000-15,000m   >15,000m
Infrastructure
Distance to natural fry       <3,000m       3,000-7,000m     7,000-12,000m    >12,000m
Distance to processing        <3,000m       3,000-5,000m     5,000-10,000m    >10,000m
plants



                                                                                           8
Distance to rivers          500-1000m         1000-2000m          2000-4000m          >4000m
Distance to roads             <2000m          2000-3000m          3000-5000m          >5000m
Distance to crab markets     <15,000m       15,000-25,000m      25,000-40,000m       >40,000m
Distance to shrimp           <1,000m         1,000-3,000m        3,000-5,000m        >5,000m
markets
Soil parameters
Soil pH                        6.5-9             5.5-6.5            4.5-5.5           <4.5 >9
Soil salinity                 8-26ppt         5-8, 26-32ppt      4-5, 32-37ppt       <4 >37ppt
Soil texture                 >75% fine       >75% medium        50-75% coarse       >75% coarse
                                            50-75 % medium         <50% all
Inputs
Agriculture                > 3 crops/year    2-3 crops/year      1-2 crops/year     <1 crop/year
by-products
Animal wastes              >10,000 tons     5,000-10,000 tons   2,000-5,000 tons   <2,000 tons/km2
                              /km2                /km2                /km2
Risk factors
Flood and cyclone             No risk        Marginally risk    Moderately risk        Severe
Winter rain                  <200 mm          200-250 mm         250-350 mm             >350
Pollution                    >4,000 m        3,000-4,000 m      2,000-3,000 m          <2,000
Elevation                      >3 m              2-3 m              1-2 m                <1
Natural indicator
Distance from mangrove     1,000-10,000m    10,000-20,000m      20,000-40,000m       >40,000m

Modeling suitable site

Following reclassifications, weights were given to the entire factor set according to the
pair wise comparison matrix of Saaty (1977). Nine sub-models were then developed
using the multi-criteria evaluation (MCE) module of IDRISI. A constraint layer was also
developed using Boolean logical operation. Finally, system-oriented models were
generated for brackish water shrimp and crab culture by using different combinations and
weightings of the modules previously created (Figure 4).

Once the MCE suitability maps had been created, it was necessary to evaluate land
allocation for crab and shrimp culture activities, which are competing for the same land.
To resolve these problems, the multi objective land allocation (MOLA) module was used.
Weights for each activity were set the same to give them equal emphasis.




                                                                                                   9
                                                                               Suitable sites for
Verification                                                                   shrimp and crab
                                                                                    culture




MOLA
Modules


                                         Preliminary assessment                                         Constraints on land use
                                          for site suitability for                                         for Aquaculture
                                               Aquaculture



MCE
Modules




Natural         Land use       Infrastructure       Support            Inputs        Environmental        Water sources         Risk        Constraints
               sub-model           sub-model       sub-model         sub-model          sub-model          sub-model         sub-model
indicator




   Mangrove      Agriculture       Paved        Agglomeration        Agricultural       Temperature        Lagoons            Disease        Mangroves
  ecosystems      Shrimp           Roads         NGO support         by-product          Dissolved          Rivers            Floods           Rivers
                   culture       Railways        Government           Animal              oxygen,          Streams          Winter rain        Cities
                  Forestry        Gravel            support            waste            Salinity, pH    Tributaries          Pollution         Lakes
                 other land        Roads        Research station                         Soil texture                       Elevation       Reservoirs
                     use         Dirt Roads       University                            Natural seeds                                          Roads
                                                                                                                                              Railways


 Figure 4. A hierarchical modelling scheme with multi criteria evaluation (MCE) and multi objective land allocation (MOLA) to evaluate suitability of
             locations for coastal shrimp (Penaeus monodon) and) mud crab (Scylla serrata) in southwestern Bangladesh. (Modified after Manjarrez and
             Ross, 1995).


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Results

The results of the study clearly highlight the suitability of the Southern parts of the region
for brackish water shrimp and crab farming in figure 5 and figure 6 respectively, with its
favored areas of high quality water, of a uniform salinity and having a consistent flow of
tidal water. These areas also have good access to road and river transport; high
agglomeration potential and they are not too far from the market outlets. It is interesting
to compare figure 5 with figure 6, in which the crab model indicates a larger area than
the shrimp farming areas, this is because of wide range of crab seed availability and their
relatively easy transport capabilities to remote places.

It is important to note that some of the areas, which have already been developed for
shrimp farming, only scored as moderately suitable. These included most of the Bagerhat
and Satkhira region, and some parts of Khulna district. In these areas soil quality is lower
because of high proportion of fine clay (Figure 2), though the major problem is the
distance from the markets and processing plants. However, some areas showed suitable
for shrimp and crab culture in the lower part of Jessore and some parts of Gopalganj
district (Figure 1). More over, these areas are not in culture practice at present due to low
salinity of available water and their distance from the natural seed sources, however,
other favourable factors such as distance from NGO, markets land use etc. have a big
positive influences.




Figure 5. GIS assisted suitable site for shrimp     Figure 6. GIS assisted suitable site for crab culture
          culture in Khulna region in Bangladesh.             in Khulna region in Bangladesh.




                                                                                                   11
Economic return

The outcomes in terms of income from one hectare of suitable area predicted by GIS are
shown in Table 3. To calculate total out comes, we need to identify the probable area
required for roads, dikes, and inlet and outlet channels and guardrooms. If 5% of land is
allowed for that purpose, the rest of the land, which will be the actual pond area is
available for culture. At present, average income from shrimp and crab production is 240
kg /ha and 300 kg/ha respectively. The price per kilogram of shrimp and crab is $8.0 and
$2.0 respectively in the domestic market. From the above calculation total outcomes
based on a single crop of shrimp could be 13,031.86 MT / year and total earnings will be
about 104.26 million US dollar per year from this region. By contrast, total outcomes
from crab culture based on two crops per year could be 54,904.85 MT / year and total
earnings would be about 109.81 million US dollar per year.

Table 3.Parameters for the economic evaluation of shrimp and crab culture.

Expenditure for Crab culture
Pond dike repairing and Labor cost                        Taka/ha         3,000
Crab seedling 5000                                        Taka/each       5,000
Feed cost to produce 300 kg crab                          15 Taka /kg     4,500
Cost of 400 kg fertilizer and lime                        5 Taka/kg       2,000
Miscellaneous expenses expenditure                        Taka/ha         2,000
Total operating cost for crab culture                     Taka/ha         16,500
Income from Crab culture
Sale of 300kg crab                                        100/kg          30,000
Benefit from crab culture(30,000-16,500)                  Taka/ha         13,500
Profit per year from two crops (13,500 x 2 + 1000)        Taka/ha         28,000
Profit in US dollar per hectare per year from two crops   US $/ha         560

Expenditure for shrimp culture
Pond dike repairing and Labor cost                        Taka/ha         3,000
Shrimp seedling 20,000                                    2.2 Taka/each   44,000
Feed cost to produce 240 kg shrimp                        40 Taka/kg      9,600
Cost of 4 kg rotenone                                     1250 Taka/kg    5,000
Cost of 450 kg fertilizer and lime                        5 Taka/ha       2,250
Miscellaneous expenses expenditure                        Taka/ha         2,000
Total operating cost for shrimp culture                   Taka/ha         65,850
Income from Shrimp culture
Sale of 240kg shrimp                                      400 Taka/kg     96,000
Benefit from shrimp culture(96,000-65,850)                Taka/ha         30,150
Profit per year from one shrimp crop                      Taka/ha         30,150
Profit in US dollar per hectare per year from one crop    US $/ha         603

US $ =50 Taka approximately (January’2000)




                                                                                       12
Figure 7 shows the allocation of lands for shrimp and crab culture by the GIS model
using the MOLA technique. A comparison was made which defined the land suitable for
two activities as being established adjacent to each other. A trade off was then made
between the proximity of one to the other for possible integration of aquaculture culture
with some types of agriculture (i.e. cattle rearing).




Figure 7. Suitable area for shrimp and crab culture after using MOLA technique to
          resolve the conflict between two culture systems.

Discussion

The areas predicted as suitable for shrimp culture from this GIS evaluation can be partly
verified by the location of existing shrimp farms in the area. Comparison has been made
with the satellite image and published data. GIS predicted that 57,157 hectares of land are
suitable for shrimp farming, whilst DOF (1994-95) has shown that 104,624 hectares are
already in operation in the area. However, there was considerable variation among the
predicted and actual locations, possibly due to the one kilometre buffer zone created
around the mangroves, that weighting method used and the different factors employed in
the models.

Much of the area ranked most suitable for brackish water shrimp and crab culture, is
situated near the riverbanks and their tributaries in the tidal zone. This ensures easy


                                                                                          13
access to saline water. However, most of the areas were only ranked as moderately
suitable because of lack of other facilities, obtaining water and drainage difficulties.
Large water bodies, which contain fresh water, were not considered of potential use
because of problems with the low salinity. Natural forest and wild life refuges,
Sundarbans, roads, rivers and urban areas were not considered for culture activities.

There are ample areas ranked as moderately suitable but not yet under culture. Crop
agriculture, which is a traditional source of income, has not yet been affected by the
development of brackish water shrimp culture. Although shrimp and crab culture in the
region have created new sources of income, however, there has been drastic reduction of
livestock and poultry in the shrimp farming areas. (Rahman, et al., 1995; Khan and
Hossain, 1996).

It is interested to note that, unlike some other areas of Bangladesh only one crop of
shrimp is being cultured in the region as the salinity of water falls to nil in the months of
July-December. This is a suitable time for rice production and fresh water prawn and fish
culture. (Rahman, et al., 1995).

Crab culture in the region is in its initial stage and there is lots of potential to expand it in
future. Crab culturists could earn many times that shown here if they intensify their
culture, by changing to a system of conventional production methods and ripe female
production and crab fattening in cages at the same time (Cholik and Hanafi, 1991).
Further, crab culture is more environmentally friendly than the shrimp culture as it can be
easily integrated with horticulture, conventional forestry and rice culture, as well as
polyculture with fish (Chong, 1993 and Chandrasekaran and Perumal, 1993). However,
mud crab culture is currently totally dependent on wild seed supply, so there is great
scope for establishing hatcheries to ensure continuous supply of seed.


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Chandrasekaran, V.S. and Perumal, P. (1993). The mud crab, Scylla serrata a species for
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Cholik, F. and Hanafi, A. (1992). A review of the mud crab (Scylla sp.) fishery and
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       Food and Agricultural Organization, Rome, Italy.

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Biography:
*
 Lecturer, Department of Aquaculture, Faculty of Fisheries, Bangladesh Agricultural
University, Mymensingh, Bangladesh. Research Scholar in the Institute of Aquaculture,
University of Stirling, working in the field of Coastal Aquaculture and GIS. Presently
involved in developing “Model for Coastal Aquaculture, Land use and Mangrove
vegetation classification in South-western part of Bangladesh using Remote Sensing and
GIS.
**
   Head of GIS and Applied Physiology group and Dean of the Faculty of Natural
science.




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