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The Caspian Sea 



I. GENERAL CHARACTERISTICS 



The Caspian Lake-Sea is the largest enclosed body of water in the world, and 

 is exceptional in its peculiarity. 



Salinity-stratification of its waters is much less pronounced than in those 

 of the Black Sea ; an oxygen supply, sufficient for the penetration of individual 

 numbers of its fauna to their limiting depths, is provided by water circulation. 

 However, the density of the population is high only in the upper horizon ; 

 below 100 m life is very much restricted owing to a shortage of oxygen. 



The Sea has been apportioned to separate zoo-geographical provinces and 

 its fauna is composed mainly of remarkable, relict, genetically heterogeneous 

 forms — the remains of relict marine faunas, formerly much more widely dis- 

 tributed, which have survived in other marine and fresh bodies of water in 

 Eurasia and which are linked in origin with the Tethys fauna. 



Immigrants from the Arctic basin, from the Black and Azov Seas (Medi- 

 terranean fauna) and from fresh waters are added to this nucleus of Caspian 

 fauna. 



In the struggle for existence the Caspian fauna is inferior to the biologically 

 stronger fauna of the open seas ; this makes the Caspian Sea exceptionally 

 suitable for acclimatization. 



Fisheries are very rich in the Sea, and its yield is original in its specific 

 composition. 



II. HISTORY OF EXPLORATION 



First period 



The first data on the Caspian Sea biology are found in the works of P. Pallas 

 (1741-1811) and S. Gmelin (1745-74). Important biological data were 

 brought back by the expeditions of K. Baer (1853-56) and O. Grimm (1874 

 and 1876). 



Second period 



The next period, of a closer, more comprehensive study of the Sea, is con- 

 nected with the name of N. M. Knipovitch, who organised and carried out 

 three expeditions in it in twelve years (1904 to 1915) before the war, which 

 interrupted its further exploration for many years. 



Knipovitch's first expedition worked in 1904, the second in 1912 and 1913 

 and the third in 1914-15. A general picture of the distribution of the depths of 

 the Caspian Sea, its currents, temperature, salinity, oxygen and hydrogen 

 sulphide content, as well as that of plankton, benthos and fish was obtained 

 by Knipovitch's expeditions. Seasonal changes in some of these phenomena 

 were also recorded. These expeditions provided the physico-geographical, 



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