34 A TEXTBOOK OF OCEANOGRAPHY 



obtained 300 fish in one haul. The upper limit of the abyssal 

 species appears to be somewhere between 500 and 450 fathoms. 



In from 300 to 350 fathoms we get fish — e.g., the hake — 

 which probably, though not certainly, are présent in sufficient 

 numbers to render commercial trawling a success. It is almost 

 certain, however, that tliis is the extrême limit for commercial 

 fishing. 



It may be taken for granted that one of the main limiting 

 factors in the bathymetrical distribution of fish is the food 

 question. According to Murray, the limit of wave action in 

 the open océan coincides with the mud line, and the average 

 depth at wliich mud begins to be deposited is 100 fathoms. 

 For a few hundred fathoms beyond the mud line animal life, 

 especially crustacea, is exceedingly abundant, and Murray 

 terms this area the " great feeding-ground " of the océan. 

 The surface layers of the organic deposits in moderate depths 

 (the organic oozes) yield an abundant food for the Benthos. 

 With rapidly increasing depths into the red clay the quantity 

 of food diminishes, and the bottom fauna is consequently less 

 abundant. The Challenger summary shows that animal life 

 was found most abundantly on the terrigenous deposits, 

 though the globigerina ooze is also very rich in organisms. 

 While the fishes of the continental shelf live on terrigenous 

 deposits, the Michael Sars experiments prove that in the 

 Eastern Atlantic most of the fauna live on the globigerina 

 ooze. Although it is true that it is not only the terrigenous 

 deposits which maintain an abundant bottom fauna — still, fish 

 of edible species are confined to the continental shelf and slope 

 and its immédiate vicinity. 



The increasing demand for demersal fish by the countries 

 of Northern Europe will unquestionably lead to an effort to 

 extend the trawling activities of British and other fishermen. 

 Since the grounds on the continental European shelf hâve 

 been fairly extensively fished already, it follows that the 

 investigation of new areas will sooner or later prove necessary. 

 Xhe bottom water of the Norwegian Sea (the area bounded 



