Autumn is relatively short. The amount and distribution of rainfall in the Mediterranean cannot be generalized. Because the primary productivity of life forms depends to a large extent on the concentration of the plant nutrient salts, it is, as would be expected, generally low in the Mediterranean Sea. The environmental conditions of the Mediterranean already described, namely, the low concentration of phosphates and nitrates so necessary for the maintenance of marine pastures, together with the poor standing crop of bottom-dwelling organisms, provide no opportunity for the evolution of a big fishing industry. The fish fauna of the Mediterranean is basically related to fauna of subtropical Atlantic with a large variety of species.
Sardines constitute the main catch in the western and northeastern parts of the Mediterranean.
Occasionally sardines also appear in relatively small quantities in the southeastern part of the Mediterranean. Closely related fishes occur in considerable quantities in the southern and southeastern region of the Mediterranean. The sprat is taken in some quantities in the most northern Adriatic. It also occurs in commercial quantities in the Black Sea. Anchovy is important in most of the regions of the Mediterranean and the Black Sea.