[9] SCIENTIFIC EXAMINATION OF THE GERMAN SEAS. 533 



and river water, whilst in the north the branch of the Gulf-stream which 

 enters the North Sea is comparatively warm. 



The northern part, as far as its temperature is concerned, entirely 

 depends on the currents of the ocean, the above-mentioned branch of 

 the Gulf-stream, and a deep, cold under-current coming from the north. 

 Thus the distribution of warmth is constantly changing throughout the 

 year ; as far as the surface water is concerned, an attempt has been made 

 to represent these changes graphically in the small maps found at the 

 end of this pamphlet. These maps have been prepared in the following 

 manner : A large number of observations made at coast stations or on 

 board ships were collected from different parts of the North Sea, and 

 from these figures the average temperature has been calculated. All 

 points having an equal average monthly temperature are connected by 

 a line. Blue indicates the lowest and scarlet the highest temperature, 

 and the transitions from blue to scarlet are indicated by green, yellow, 

 and orange lines. In examining these maps the above statements will 

 be found correct. In January the water is warm in the north and in 

 the extreme south, in the former region on account of the Gulf-stream, 

 and in the latter on account of the warm water from southern latitudes. 

 Along the German coast the water is cold on account of the Elbe and 

 Baltic water. February closely resembles January ; and even in March 

 the water on our coast is cold. In April this condition begins to be 

 reversed, and the water on our coast grows warmer; in May and June 

 the temperature of the water is low as far as the Doggerbank, whilst 

 during these months the shallow southern part and the coast waters, 

 which receive much Baltic and Elbe water, are much warmer. 



From July to September the water keeps warm in the southern and 

 southwestern parts of the North Sea, a circumstance well known in our 

 North Sea watering places, which are frequented till far into September. 

 In October the water begins to cool oft', beginning at the Baltic, and 

 continues to grow cooler during November and December. 



These graphic representations are, of course, only in the nature of. a 

 first attempt, which will have to be improved and supplemented by 

 future observations, especially in deep water; but even the little we 

 know regarding these changes in the temperature of the water is suffi- 

 cient to show that they must exercise a decided influence on the migra- 

 tion and life of the fish. The appearance of the herring first in the 

 north, then gradually farther south, the wealth of fish near the Dogger- 

 bank, which is washed by cold water during the months of April, May, 

 and June, are hints pointing to the intimate connection existing between 

 the temperature of the sea and its animal life. 



To further investigate this connection should be the first object of 

 scientists during the next few years ; and practical fishermen can greatly 

 aid in solving the problem, if they will watch those natural conditions 

 which either rewarded their toil by rich hauls of fish, or which failed to 

 crown their most earnest endeavors with success. 



G. KAESTEN. 



