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Simultaneously, rather extensive fish stocks surveys were carried out in this region by MSRC andFAO/Norway cruises of R/V Dr F. Nansen, allowing us to consider exploitable resources of thisregion for the first time interrelated with the complex and oscillating ecosystem of the Gulf of Aden.Preparation of this paper would not have been possible without the generous support andcooperation from the Institute of Marine Research, Bergen, Norway. In addition to allowing us to usetheir fish stock and hydrographic data, ship facilities were provided for our research team during thesummer of 1984 when our ship could operate due to heavy monsoon seas. Assistance of scientistsbilaterally assigned to PDRY from USSR is gratefully acknowledged.MATERIAL AND METHODSOCEANOGRAPHY AND PELAGIC B IOPRODU~~Since February 1984, 10 monthly and 4 seasonal cruises were carried out on R/V Ibin Magid(except in August 1984, by R/V Dr. F. Nansen); stations are shown in Figure 1. Standardhydrographic sampling and measurements were performed at all stations down to a depth of 1,000 mwhen applicable. Hydrographic samples were taken by Nansen bottles, nutrient/phytoplanktonsamples by atoxic Van Dohrn samplers. Samples for nutrients were taken at the surface, 50, 100,200, 500, 800 and 1,000 m; phytoplankton/chlorophyll at surface, 50 and 100 m. Zooplanktonsamples were taken from vertical hauls (twice at 30 - 0 m, one sample being preserved dee -frozen forsubsequent biomass determination, and at 100 - 0 m) with a WP-2 net (mouth 0.25 m ?, mesh 200pm).Except for pH and oxygen, which were measured on board, all samples were preserved anddeep frozen (chlorophyll samples were filtered immediately after the sampling and dry filters frozen)because laboratory facilities were not available on the ship. Consequently, subsequent analyses,although carried out soon after the cruises, showed quite doubtful results for nitrite and ammonia,while the rest of nutrient analyses delivered consistent results.Salinity was determined by the Grasshoff modification of Mohr-Knudsen titration. Nutrientswere analyzed spectrophotometrically: phosphate after Murphy and Riley, ammonia after Solorzano asmodified by Koroleff, nitrite after Bendschneider and Robinson, nitrate by the Grasshoff modificationof the Moms and Riley reduction method, silicate after Koroleff modification of the Chow andRobinson procedure. Chlorophyll determinations were carried out basically as recommended bySCOR/UNESCO; however, the Humphry trichromatic formula was applied. Zooplankton biomasswas obtained as displacement volume, dry weight (70°C) and ash-free weight (500°C). Processing ofpreserved zooplankton samples for quantitative taxonomic studies followed procedures asrecommended by FAO/STIRN. Quantitative taxonomic analyses of preserved phytoplankton werecarried out by the improved Uttermoehl settling-inverted microscopy technique recommended byscoR/uNEsco.FISHERIES BIOLOGYDemersal FishThese were surveyed by the following trawling methods:0R/V Ibin Magid trawl of 28 m headline with a vertical opening of 4 m. The mesh inthe codend was normally 65 mm but sometimes was changed to 120 mm when trawlingfor cuttlefish. Trawls were taken at 3.2 to 3.6 knots for 1 to 3 hours duration; depthswere between 15 and 120 m. In total, during 1983-85 on 9 cruises over 300exploratory trawls were made, covering the whole stretch of Yemeni coastal waters, yetfocusing upon traditional trawling grounds in the eastern part.258