The Mediterranean Sea is a miniature ocean with a surface area of less than 3 million km2 and a volume of just over 4 million km3. A subterranean ridge between Sicily and Tunisia forms a sill at a depth of about 200 m separating the eastern and western basins with depths exceeding 3 000 m. Water from the Atlantic Ocean enters the Mediterranean through the narrow Straits of Gibraltar and is carried eastward along the African coast by permanent surface currents. Narrow channels connect the Mediterranean with the Black sea through the Bosporus Straits, and with the Indian Ocean through the Suez Canal. The current pattern with the high insolation rate and substantial evaporation of the Mediterranean increases the salinity from 36.2 to 39.2 ppt from west to east.
The Mediterranean is low in nutrients and is reported to be the most impoverished sea in the world. Scientists have observed that only those areas under Arctic ice or in certain tropical regions are less productive than the Mediterranean as a whole. However, the waters in some portions of the Mediterranean are much more productive than others. Also, more than 1 million ha of shallow brackishwater basins or lagoons occur along the Mediterranean coast and most of these are highly productive.
The yield of fish from the Mediterranean has increased gradually from 572 000 t in 1966 to 772 000 t in 1976. The increase has been largely from expanded fishing efforts for pelagic species. The yield of demersal fish is relatively small and during the last decade has remained between 250–300 000 t yearly.
Although the fisheries production from the Mediterranean is less than 2 percent of the world's marine fisheries landings, the value is proportionately higher, about 5 percent of the value of the total world catch. The reason for this is the high price of the Mediterranean fish, especially of demersal species, which sell for about seven times the average world prices for this category.
The consumption of fish in the countries bordering the Mediterranean and the Black Sea rose from 2.7 to 3.7 million t between 1960 and 1970, while the population of the area increased from 265 to 308 million. It is estimated that by 1985, the population will have increased to 380 million and the annual demand for fish will rise to 5.5 million tons.
The landings from the Mediterranean are not sufficient to meet the demand for fish in the countries of the region. At the present time, two-thirds of the fish consumed in this region come from other areas, mainly from the Atlantic, where several Mediterranean countries engage in fishing. In addition, imports of fishery products supply about 15 percent of the total consumed in the region.
Most of the demersal stocks distributed along the northern coast of the Mediterranean are regarded as heavily fished. Increased fishing efforts are not recommended and regulatory measures will be needed to maintain present yields and catch rates. A moderate increase in the catch of demersal species is reported to be possible along the southern coast of the Mediterranean, particularly along the western half. Apparently, coastal pelagic stocks can be more intensively fished.
On the whole, there is a low probability of maintaining increased landings of demersal species from wild stocks. Therefore, it is likely that the demand will continue to exceed supply resulting in increased prices for these species.
Given the high demand for demersal species, crustaceans and molluscs and the low probability of increasing landings from wild stocks, it is natural to consider aquaculture as a means of fulfilling the demand. There is a long tradition of oyster and mussel farming in the Mediterranean area, as well as use of coastal lagoons, to retain fish for a growing season before harvest. The technology for farming of fish, crustaceans and molluscs has developed rapidly during the last decade, and these techniques already produce nearly 10 percent of the world's supply of aquatic foods. The wider application of aquaculture techniques in the Mediterranean might provide a reliable means of supplying the projected demand for certain economically important species in the Mediterranean region.
The types of aquaculture proposed for the region would need to take into account the special environmental and social characteristics of this area. With unproductive water of high salinity and moderate temperatures, the culture of native species in floating cages, ponds, tanks, or raceways, with artificial feeding would be appropriate. Molluscs and fishes might be grown in coastal lagoons or estuaries where run-off from the land provides additional nutrients to stimulate phytoplankton production.
Looking to the future, controlled environment systems may be developed in which the aquaculture species are maintained under optimum conditions for rapid growth and high survival and are provided with nutritionally satisfactory diets. Such systems are already being tried in the case of eels in the Mediterranean region and may become useful for the culture of additional species in the future.
The following sections of this report examine the potential for aquaculture of marine species in this region and describe actions needed to increase the production of aquatic foods by farming. The report also examines the need for cooperative efforts and sharing of aquaculture technology among the Mediterranean countries and proposes a regional programme to facilitate this.