2. Survey coverage

During each of the main surveys in the post-monsoon season in September-November 1979. and the pre-monsoon season in March-April 1980 the Burmese waters between the border with Bangladesh in the north and that with Thailand in the south was in principle covered twice. There was thus a total of four coverages as follows:

1st	coverage	25/9-18/10	1979
2nd	coverage	23/10 18/11	1979
3rd	coverage	5/3-1/4	1980
4th	coverage	5/4-27/4	1980

The first and third coverages represented total fixed grid overviews while the research efforts of the second and fourth coverages were concentrated within areas which were found to be of particular interest with regard to fish abundance and distribution. Figures 1 to 4 show the course lines followed during the various parts of the survey and the location of the fishing stations and hydrographical stations worked. The main transects are spaced approximately 30 nautical miles apart and run from a depth of about 15 m seawards with a maximum extension of 110 nautical miles. During cruise 3 also the Coco islands region was covered. Seven hydrographical sections were worked on cruises 1 and 3, three off Arakan, two in the Delta area and two off the Tenasserim coast. Bottom- and pelagic trawls were operated at close to 400 fishing stations.

In the further analysis of the findings the total survey area will be divided into the following four geographical sub-areas which are likely also to represent main ecological divisions:

The Arakan coast, boardering the Bay of Bengal with a harrow shelf and few inlets down to about 16º Lat.N.

The Delta area, covering the mostly shallow and slightly sloping wide shelf between 16º and 13º30' Lat.N. and about 94º to 98ºLong.E and dominated by the influence of the outflows of the Irrawaddy and the Salween rivers.

The Tenasserim coast, south of 13º30'N boardering the Andaman Sea, with numerous fjords and inlets and with shallow and medium depths ; and finally

The Deep Sea Trawling Ground on the slope of the shelf from 200 to 400 m depth off the Tenasserim coast, from abt 13ºLat.N to 10°Lat.N.

Figure 2 Survey routes and stations 23 Oct-18 Nov. 1979

Figure 3 Survey routes and stations 5 March-1 April 1980.

Figure 4 Survey routes and stations 5 April-27 April 1980. The area within frames on the Delta is the trawl survey area dealt with later in the text.

Although these sub-arears have been covered twice in each season all the observations and findings during one season have been analysed and interpreted jointly so that the results are presented as deriving from two surveys, one in the autumn, September-November 1970 and one in the spring, March-April 1980.

Estimates have been made of the area covered by the investigations. These are based on the distribution of the survey grids shown in Figures 1-4. Table 1 shows these estimates. Since the main fish distribution is limited to the shelf area, the parts of the shelf which was covered by the survey have also been calculated. The outer regions of the shelf (to the defined limit of 200 m depth) have generally been fully covered in a. sub-areas, but the inshore shallow parts could often not be covered because of a depth limit of about 15 m for safe operation of the vessel. Estimates have been made of the extent of the shallow inshore shelf which has been left uncovered in the various sub-areas. The estimates of the fish biomass will be adjusted for these areas which had to be left (...) of the surveys.

Table l. Area of investigation, degree of covering and shelf area in Burmese waters

Area of the investigations (nm2)			Area of the shelf covered (nm2)		Shallow waters not covered (nm2)		Shelf area (nm2)
AREA	Oct-Nov -80	Mai-Apr -80	Oct-Nov -79	Mar-Apr -80	Oct-Nov -79	Mai-Apr -80
Arakan court	17.000	16.000	9.400	9.400	2.000	2.000	11.400
Delta area	25.600	35.100	23.800	29.500	9.000	4.800	34.300
Tennasserim coast	22.800	25.300	15.300	17.800	5.700	3.200	21.000
Total	65.400	76.400	48.500	56.700	16.700	10.000	66.700

It is of interest to consider the "survey-" or "sampling intensity". A measure of this is the quotient between the distance travelled during the actual echo-survey and the area of investigation. These are:

Autumn	Spring

For each 100 n.m.² (10x10 n.m.) of survey area there (..) an average thus 12 n.m. of survey track during autumn and 11 n.m. during spring. As is evident from Figures 1-4 some areas were much more densely covered than others e.q. the Delta area.

Figure 5 Bottom conditions Arakan Coast: 1) even flat bottom, 2) uneven bottom, 3) rough bottom, 4) steep slope.