[3] SCIENTIFIC EXAMINATION OF THE GERMAN SEAS. 527 



plainly demonstrated the intimate connection existing between the de- 

 velopment of this iish and the condition of the water. 1 



Here is the point at which the fishermen themselves can aid and fur- 

 ther the fishing interests, if they will give careful attention to the spawn- 

 ing of all the more important fish and to the accompanying general con- 

 ditions of tlie sea. 



In the following we shall endeavor to give all the results which have 

 been gained by observations of those conditions in the Baltic and the 

 North Sea which probably exercise a considerable influence on the fish- 

 eries. 



2. There are three conditions of the sea- water which exercise a decided 

 influence on animal and vegetable life, viz: (1) temperature, (2) saltness, 

 (3) currents; and all three are influenced by the atmosphere and the 

 nature of the bottom. Another important fact as regards the condition 

 of the water of the Baltic and the North Sea is their varying connection 

 with the ocean, and the varying quantity of fresh water flowing into 

 them from different streams and rivers. The conditions of these two 

 waters are so different that we must treat of them separately. 



A. The Baltic is a very shallow sea. If we except the deep waters 

 east and southeast of Gotland we rarely find a greater depth than 100 

 meters. The three channels leading into the North Sea, the Sound and 

 the two Belts, are shallow. Large streams flow into the Baltic, carry- 

 ing into the sea raiu and snow water from a territory three times the size 

 of that from which the North Sea is supplied. When two masses of 

 water of different weight meet, the heavier of the two will generally 

 sink lower down ; the heavier water from the Kattegat will therefore 

 enter the Baltic and form its undercurrent, whilst the lighter water of 

 the Baltic flowing into the Kattegat will become its surface water. On 

 account of the very large quantity of fresh water flowing into the Bal- 

 tic (especially in spring, when the ice and snow begin to melt, and in 

 summer during continued rainy seasons), the upper current which flows 

 out of the Baltic is much more powerful than the undercurrent which 

 enters it. 



The saltness of the Baltic therefore decreases from west to east, but not 

 uniformly; but, influenced by the wind, sometimes quick and at other 

 times slow, and also influenced by the nature of the bottom, quicker in 

 one direction than in another. 



Continued east wind favors the flowing of the water of the Baltic 

 into the Kattegat ; the upper current containing but little salt, becomes 

 stronger in the Sound and the Belts, and the salt Kattegat water is 

 forced back. Continued west wind, on the other hand, drives the water 

 east and favors the entering of salt water. The advance of the last- 

 mentioned water from west to east varies considerably, according to the 



Compare: Dr. H. A. Meyer, " Biologische Beobachiungen bei EUnstlicher Aufzucht det 

 Hering-s der ivestlichen Ostsee." Berlin, 1878. (Biological observations made during the 

 artificial rearing of herrings in the Western Baltic.) 



