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OCEANOGRAPHIC CONDITIONS PELAGIC PRODUCTIVITY ANDLIVING RESOURCES Ik THE GULF OF ADENJ.STIRN*, R.EDWARDS*, J. PIECHURA*, M . SAVICHS, M. GHADDAF,M. FADEL, F. MUTLAQ, 0. SABIH, A. SAYED, S. SHAHER AND Z. ZUBAIRIMarine Science and Marine Resources Research CentreAden, P.D.R. Yemen*UNESCO Field Project 703/PDY/40gAzcherniro Kertch, U.S.S.R. (bilateral assignment to P.D.R. Yemen)INTRODUCTIONThe Gulf of Aden extends east-north-eastward from the narrow Strait of Bab-al-Mandab to aline between Ras Bag-hashwa (east of Mukalla, P.D.R. Yemen) and Ras Asir (northeastern comer ofthe Somali Peninsula) where it opens to the North Arabian Sea. Its approximate surface area is 220 x1@km2, and the average depth is about 1,800 m.Not as much for its size (which is quite considerable) but for a number of formidableoceanographic phenomena, the Gulf of Aden presents a rather unique, large ecosystem which deservesscientific attention. In addition, its extraordinary biotic richness traditionally has provided considerableamounts of sea food for the inhabitants of the surrounding arid lands. Much more sea food can beexpected in the future, provided a rational fisheries development is based upon the scientificknowledge of this ecosystem and its exploitable potential.The Gulf of Aden was “a highway for international trade almost at the start of recordedhistory” (BEHRMAN, 1981). It also lies on the route of most research ships working in the IndianOcean. However, surprisingly little information on its oceanography or bioproductivity has beengathered. Even the International Indian Ocean Expedition (IIOE 1962-63, subsequent compilations ofcollected data (IIOE atlases: IOBCPANIKHAR, 1968-70; KREY and BABENARD, 1976; WYRTKI,1971) and numerous resulting scientific papers did not fill the the gaps in knowledge significantly.Although these documents gave the main oceanographic and bioproductivity characteristics of the Gulfof Aden, they were extrapolated from very few data and thus could not adequately describe the realconditions; e.g. primary productivity is interpreted on the basis of 8 carbon assimilation and 35chlorophyll a measurements covering all seasons and depths. Using Behrman’s expression that priorthe IIOE the Indian Ocean was a “forlorn ocean”, so the Gulf of Aden during the IIOE was a rather“forlorn gulf ’. Fortunately, in the adjacent regions of the Arabian Sea, namely Omani shelf-watersand the area of the Somali Current, where more systematic investigations were focused during andafter the IIOE, some detailed studies (e.g. BRUCE, 1973; CURRIE et al., 1973; SCHOTT, 1983;SMITH, 1982, 1984; SWALLOW and BRUCE, 1966; WARREN et al., 1966) were carried out onphenomena whose principles apply also to the oceanographic- bioproductivity conditions of the Gulf(e.g. upwelling, de-oxygenation, etc).Based on information available since the IIOE, the only oceanographic research in this regionhas been carried on by Soviet research vessels, and by FAO/Norway fisheries research cruises of F WDr. F. Nansen (1975-76 and 1984). The great majority of these cruises, however, emphasized fishstock surveys and other applied purposes, thus oceanographic research, using only just the mostessential hydrographic measurements, was a second priority. In spite of that, however, a number ofimportant scientific papers on the hydrography, nutrients, phytoplankton and zooplankton significrntlyincreased the specific knowledge on the Gulf of Aden (GAPISHKO, 1971; KHIMITSA, 1968a,b;SAVICH, 1968, 1969, 1979; SERIY, 1968; SUKHANOVA, 1969). Of course the most importantcontribution of these investigations was the extensive knowledge on exploitable sea-food resources ofthis region which will be summarized in this paper.255