OCEANIC DEPOSITS AND BOTTOM FAUNA 35 



roughly by Norway, the Shetlands, Iceland, Greenland, and 

 Spitsbergen) is quite cold, most of it below o C., the abyssal 

 plain itself having water of temperature below - i C. So far 

 as our information goes, the valuable trawl fish, Gadidai (cod 

 family) and Pleuronectida; (plaice family), are absent from 

 this cold water. A few fish, of relatively inferior edible 

 qualities, are alone captured in the deeper waters. The coastal 

 banks off Greenland, Jan Mayen, and Spitsbergen, which, 

 unlike those off Iceland and in Barents Sea, have not yet been 

 explored by commercial trawlers, are frequented by certain 

 cold-water species about whose distribution and abundance 

 more information is required. The only Gadoid at all 

 abundant is the polar cod (Gadus saida). Other species that 

 may be taken are the Norway haddock (Sebastes norwegicus), 

 a species of gurnard, and the saithe. There can, however, be 

 no doubt that the distribution of certain species of fish is closely 

 connected with the presence of water of a certain temperature, 

 with its characteristic invertebrate fauna. For instance, the 

 southern limit of the characteristic northern species coincides 

 with the isotherm of 10 C. At a depth of 50 fathoms this line 

 runs across the Atlantic from the border of the northern 

 and middle States of North America to the north-west of 

 Ireland. 



On the west side of the Atlantic the isotherms between 

 12 C. and 4 C. are at 50 fathoms closely squeezed together, 

 whereas on the east side they are widely separated. West of 

 the British Isles the influence of the Gulf Stream plays an 

 important part, so that here such northern species as the cod, 

 saithe, tusk, and halibut, are not captured. 



The westward limit of our trawlers' activity is limited by 

 the line to which the fauna of the continental shelf extends, 

 and this may be taken to be, for practical purposes, 300 

 fathoms, up to which commercial trawling is successful, the 

 fish found at the greatest depths here being ling, hake, and 

 bream. The average temperature at 300 fathoms west of 

 Ireland is approximately 10 C. The distribution of the 



