Remote Sensing Applications for Marine Fisheries Resources in Bangladesh

Md. Obaidul Quader
Principal Scientific Officer
SPARRSO, Dhaka-1207, Bangladesh

INTRODUCTION

The Bay of Bengal: It lies in the north east corner of the Indian ocean. Bangladesh is situated at the head of the Bay and other coastal states bordering the Bay are India and Srilanka on the west and Myanmar and part of Thailand on the east. The length for the coastline for Bangladesh is about 710 km.

The Bay of Bengal covers an area of 8,38,392 square miles (21,72,000 sq. km), it occupies a total volume of 13,47,335 cubic miles (5616000 cubic km) and has a mean depth of 8,484 ft (2,586m). The deep basin of the Bay of Bengal is roughly ‘U’ shaped and lies at depths of upto 14,764 ft (4,500 m).

All the major river systems in India, Bangladesh and Myanmar discharge into the Bay of Bengal. It has been estimated that on the average 1300 million acre feet of fresh water is discharged per annum into the Bay. The annual range of temperature is 25-30°C while the salinity varies from 20-34.5 ppt.

The territorial sea limit is 12 nautical miles measured from the base line. For all practical purposes, the territorial sea including the air space above, its bed and subsoil is recognised to be within the complete sovereignty of the coastal state. The exclusive economic zone extends to 200 nautical miles from the base line. It comes out to be 40,000 square miles for Bangladesh. In this zone, the coastal state has sovereign rights for the purpose of exploration and exploitation conserving and managing the natural resources, whether living or non living of the sea bed and subsoil and the adjacent waters and with regard to other activities for the economic exploitation of the zone such as production of energy from the water, currents and the tide. The most prominent physiographic feature of the Bay of Bengal is the Swatch of No Ground - a submarine canyon lying off the Ganges-Brahmaputra Delta. The Bay floor is characterized by a number of other topographical features also, namely the Bengal Deep Sea Fan, the Nicobar Fan, the Ninety East Ridge, Chagos-East Coast Trench and Java-Sunda Trench. Colour of water in open part of the Bay is dark blue which gradually changes to light blue to green towards the coast. Transparency is found to be 40-50m in some places. Dense turbid water is observed only in the coastal river mouth and in the upper layer and below 30m lies the clear water.

Remote Sensing Applications in Determining Parameters of Marine Fisheries Resources Marine resource development specifically fisheries development is one of the major areas demanding immediate attention. In this field work carried out in other countries have shown that remote sensing can be successfully used in mapping and monitoring of ocean features like chlorophyll content, thermal fronts, eddies, upwelling, concentration of sediments etc. For locating probable areas in the open ocean having fish schools such information is very useful. Phytoplankton pigments (Chlorophyll) an in the sea waters are the prime photosynthesizes in marine food chain which in turn terminate as pelagic or benthic newton. These data can help estimate primary productivity and information on the global carbon cycle also.

Turbidity also can be studied from satellite data which protect fish larvae from solar radiation and causes disease in the gills of fish. Migration study of eurahaline and stenohaline fish also may be made from satellite data.

Determining sea surface temperature data from NOAA satellite and their possible application in locating fish habitat in the Bay of Bengal: The Bay of Bengal offers a potential source of fisheries resources for Bangladesh. A survey previously conducted by the Bangladesh Fisheries Development Corporation (BFDC) and the FAO (1968 to 1971) covered an area of 26,000 sq. km, mostly in areas north of latitude 20°40’N and bounded by longitude 89° to 92°30’E. This survey identified four major commercial fishing grounds. However, locations of these fishing grounds are not fixed. The locations differ due to changes in physical, chemical and biological factors, so the key problem is to locate and determine the productivity of fish production areas for future development and management.

Laurs (1986) reviewed fisheries applications of satellite oceanic remote sensing in U.S.A. Silas et al (1985) stated that the 15°, 20° and 23°C isotherms are the lower normal bounderies of occurrence of albacore, skipjack and yellowfin tuna, respectively, in the Indian Ocean. Joseph and Somavashi (1985) stated that the tuna contributed to 37 percent of the catches from the research vessel ‘Matsya Sagundi’ in the Bay of Bengal. They also mentioned that space technology applications in this regard could be of immense help. Tuna constitutes an important shared migratory stock in the Bay of Bengal among India, the Maldives and Srilanka. Thus remote sensing techniques may play a vital role in the management of marine fish resources.

The Analysis of Multichannel Sea Surface Temperature: The NOAA-9 (AVHRR) data used in this study are high resolution, local area coverage (LAC) data, acquired over the region and received at SPARRSO’s ground station. These data were formatted on CCT’s and preprocessed to the 1b level of the NOAA NESDIS and SPARRSO formats. Strong and Mclain (1984) algorithm MCSST = 1.0346 T11 + 2.58 (T11 + T12) - 283.21 was used to calibrate Multichannel Sea Surface temperature (MCSST) with the data from the images listed in Table 1. 28 tapes of different dates and months of the years 1985, 1986, 1987 and 1988 were analysed using VAX-11/750 computer and I²S software. Out of these 28 tapes 5 had corresponding sea-truth data obtained from the Marine Fisheries Research, Management and Development Project, Chittagong. This permitted the verification of the satellite observations with the field data.

Table 1. MCSST data with dates and sea-truth data

This study showed a temperature difference between calibrated MCSST data and sea-truth SST data. It ranges between 0.2° and 3°C. These temperature differences are due to differences of channel, time and location on the same day. It was found that coastal water is often colder than deep sea water, but the temperature differences are small. MCSST ranges from 1° to 3°C. Only a few images of the monsoon season were analysed due to cloud cover disturbances. A warm core zone was found along Coxs Bazar and the Myanmar coast. Some interesting eddies and circulation patterns were observed in the winter MCSST data. We assume that these patterns may have some correlation with pelagic fishes in the Bay of Bengal and that in the future these correlations may be established in collaboration with the Department of Fisheries.

The pelagic fishes that are identified in the Bay of Bengal are as follows: mackrel, tuna, scad, herring, sardine, shad and anchovy. If good correlations between the locations of some of these fish and MCSST data can be made, it will be easier to locate and commercially exploit these fisheries.

Determining Chlorophyll Content of the Bay of Bengal using CZCS Satellite Data: The ocean colour is dependent indifferent materials present in the water, mainly phytoplankton and mineral particles, plus water itself. Each microscopic algae is full of a photosynthetic pigment, the chlorophyll which is green (strongly absorbing the blue light). This change in colour is detected by satellite sensors which have different bands in the visible spectrum, especially the blue band (440 nm).

The relationship between sea-surface colour and pigment concentrations forms the basis of the biological applications of CZCS data. As measures of chlorophyll-a (plus phaeopigments), these concentrations provide a quantitative determination of the spatial and temporal distributions of the surface phytoplankton biomass These data can help estimate primary productivity and provide information on the global carbon cycle.

Six CZCS local area coverage scenes of Bay of Bengal were chosen as the cloud free images available at NESDIS/NOAA archive center (Washington) for the 1978 to 1985 period. One tape was analysed at SPARRSO with VAX/11 - 750 computer and SEAPAK software. Rest tapes were analysed at NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA with same computer and software. Optical disc drives and a video disc player were also used for selecting the images at Goddard. The tapes which were analysed were of Dec 3’ 1979, February 1927 ‘82, January 2’ 1983, January 13’ 1983 and April 25 ‘85.

Result shows that Bay of Bengal has 0.1-10 mg/m³ chlorophyll content from the coast to deep sea. The coasts are more enriched with chlorophyll than the deep sea. This result has been varified with seatruth data of chlorophyll content from International Indian Ocean Expedition (Krey 1976). Average surface chlorophyll for the Bay of Bengal were 0.224 mg/m³ (Qasim 1978).

Use of Satellite Measurements in Fisheries-Aid products for fishermen: Several projects and programmes have used or are using satellite derived ocean data in fisheries-aid products which are distributed to some fishermen of USA, Japan, China and other developed countries by a variety of mechanisms, including radio facsimile transmission, voice broadcast, by mail, telephone copier and thermal chart.

Charts showing the locations of oceanic thermal boundaries are derived from polar orbiting satellites and are provided to commercial and recreational fishermen for using in locating potentially productive fishing areas associated with oceanic frontal features. High resolution infrared images from the GOES satellite and ship reports are used in the preparation of charts for waters off the Atlantic-Coast, which are distributed to fishermen and other interested users. Of particular interest to fishermen these charts show (a) the outer limit of the shelf water mass, in which many fishery species reside, and (b) the numbers, sizes and persistence of warmcore Gulf Stream rings, which can markedly alter conditions on the fishing grounds. Charts based on GOES infrared imagery are also prepared to show the path of the loop current in the Gulf of Mexico and are mostly used by recreational fishermen.

In the USA experimental ocean colour boundary charts based on CZCS imagery were distributed to US west coast fishermen. They were produced at almost weekly intervals depending on cloud conditions and cover coastal areas up to 700,000 km² between Guadlupe Island and Vancuover Island. NIMBUS-7 CZCS passes along the Pacific coast were collected and processed in real-time, and, and transmitted by radio facsimile the following day to fishing boats. The colour boundary charts and photographs are used primarily by commercial albacore and salmon fishermen, and recreational fishermen in southern California (Laurs 1986). Sea ice forecast charts derived from Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) and AVHRR infrared imagery are prepared for regions of Alaska and transmitted by radio facsimile to fishermen and other marine users. In Japan some fishermen use their own portable satellite receiving stations in their fishing boat. In China some remote sensing centers produce thermal charts for the fishermen using satellite data. In India also some work has been done experimentally to provide satellite data to the fishermen.

References

1. J. Krey, 1976. Phytoplankton production, Atlas of the International Indian Ocean Expedition. IOC, Institute Fur Mereskunde - Kiel University, December, P. 23.

2. Joseph, K.M. and V.S. Samavabshi, 1985. Marine Fishery Resources Survey and role of satellite remote sensing in the assessment of pelagic fisheries resources in India. Proceedings of the seminar on Remote Sensing in Marine Resources, Marine Fisheries Research Institute, Cochin, India, April, P. 1-5.

3. Laurs, R.M. 1986 Application of Satellite Remote Sensing to U.S. Fisheries. UN/IOMAC Regional Meeting of Experts, Colombo, Srilanka, Sept.

4. Qasim, 1978. Distribution of Chlorophyll-a in the Indian Ocean. Indian Journal of Marine Sciences Vol. 7, December, pp. 258.

5. Silas E.G., P.V. Pilai and U.K. Balachandan, 1985. Marine Fishery Resources Survey and Role of Satellite Remote Sensing in the Assessment of pelagic Fishery resources in India. Marine Fisheries Research Institute, Cochin, India, P 5-1, 5-2, 5-3.