56 DEPTHS OF THE OCEAN chap. 



the geographical distribution, horizontal as well as vertical, of 

 the most important species of fish, especially during the spawn- 

 ing period, when many of them are most sought after, and when 

 each species may be supposed to congregate at localities where 

 the natural conditions, such as depth, salinity, and temperature, 

 acre especially favourable and characteristic. These breeding 

 places have been discovered partly by searching for the spawn- 

 ing fish, and partly by charting the distribution of the newly- 

 spawned eggs, which float immediately above the shoals of 

 spawning fish. 



The development and growth of the fish, and the geographical 

 distribution of the different stages, formed another important 

 subject for our scientific studies. By various means it is now 

 possible to ascertain the age of the different individuals in a 

 shoal of fish, and we are in consequence able to study the growth 

 of fishes in different areas. 



Some of our fishing experiments have had an immediate 

 influence on the development of the fishing industry, and have 

 led to fish being found on hitherto unutilised banks, which have 

 since turned out to be profitable fishing grounds. The study of 

 the natural history of fishes may be said to have as its main 

 object the widening of our knowledge regarding all the physical 

 and biological phenomena on which depend the life of the fishes 

 and the fishing industry. 



During the winter of 1909-10 a great deal of time was spent 

 in preparing the " Michael Sars " for an extended cruise in the 

 North Atlantic, in selecting the route to be followed, and in 

 preparing instruments and apparatus of the latest and most 

 approved patterns. 



A glance at the depth map is sufficient to make it clear that 

 the greater part of the North Atlantic is deeper than 2000 

 fathoms. The coast plateaus off Africa, Spain, and the United 

 States are very limited, and the continental slope is, as in the 

 Norwegian Sea, very steep. The bathymetrical curves for 500 

 and 1000 fathoms lie in close proximity to one another. Only 

 off Newfoundland and from the Bay of Biscay northwards along 

 the western shores of Ireland and Great Britain do we find the 

 continental shelf or coast banks widening out into tolerably 

 broad plateaus. From the coast banks round Iceland a low 

 ridge extends in a south-westerly direction, known as the 

 Reykjanes Ridge. This is continued southwards as the Dolphin 

 Rise, with deeper water on either side. From this low ridge 



