Introduction

In accordance with the contract between the Food and Agriculture Organization of the United Nations (FAO) and the Institute of Marine Research, Bergen, the fishery resources of the western part of the north Arabian Sea were surveyed with the research vessel "Dr. Fridtjof Nansen" in the period 14 February 1975 to 24 November 1976.

Whilst the work is adequately described by the general term "resources survey", the objectives more specifically were:

a) to contribute to the knowledge of the composition of the "fishery" fauna of the region, directing attention primarily on species of present economic importance but taking due note of other species (for example, the mesopelagic) and of other faunistic elements (for example, zooplankton);

b) to add to knowledge of the distribution of the more important species of fish of the region and especially show the variations in distribution from season to season;

c) to measure the size of the stocks of each species, in the region generally and in distinct parts of the region;

d) to obtain some estimate of the magnitude of the catch that might be available from each stock, with some indication of appropriate fishing seasons, grounds and catch rates;

e) to ascertain, by fishing trials and from observations of the behaviour of each species (schooling habit, vertical migrations etc), the gears and methods that might be employed in the fisheries of each part of the region.

The survey was effected through 6 cruises in which work was carried out in every month of the year except July, and thus covered both monsoon periods. (See Figure 1).

The operational characteristics of the survey are summarized in Table 1 and are represented in Figures 2 to 6. It will be seen that the continental-shelf space was traversed several times, and oceanic space beyond the shelf were also visited. In the course of these traverses, acoustic observations were made uninterruptedly, surface observations were recorded, fishing was carried out frequently (570 stations) although insufficiently, as it proved (see below), and oceanographic observations were made even more frequently (939 stations). The result of this work was a very considerable quantity of data which, upon analysis, yield much evidence on the fishery resources of the region, of relevance to the several objectives set for the survey.

The region covered in this survey included the Pakistan coast but since a special survey was subsequently made of that coast, and the results from this survey were assimilated to that other, no reference is made in this report to the results from that coast. Some data obtained from observations on the North Kenya Banks, made during Cruises 1, 3, 4 and 6, have also been excluded. Data on mesopelagic fishes, plankton and large pelagic fishes have not been considered in the analyses for this report since they have been, or will be dealt with elsewhere, although some reference to main results from those other studies is made where appropriate.

A report was made of each cruise, shortly after its completion, and submitted to FAO (Cruises 1 and 2 were reported on together); a preliminary final report was prepared in August 1977, and submitted to FAO, it was subsequently discussed at the FAO/Norway Workshop "on the fishery resources of the north Arabian Sea" which took place in Karachi, Pakistan, in January 1978. From these and other discussions it became clear that the data obtained from this survey could yield somewhat more information and that perhaps more accurate estimates could be made of biomass. Preparation of the present report was therefore undertaken, to make use of a different treatment of the acoustic data (especially to calculate the variance of the recordings of each sector and to calculate confidence limits for estimates of biomass) and fuller use of the biological information.