OCEANIC DEPOSITS AND BOTTOM FAUNA 33 



fathoms with an otter trawl much larger and more effective 

 than any of the gear used on the Challenger. This net had a 

 head-rope 50 feet in length, and the opening of the net may 

 be considered to be not much less than this. At 2,800 fathoms 

 it took over five and a half hours to shoot and over six hours 

 to haul the trawl. Unfortunately, after three successful hauls 

 from the abyssal plain the trawl was lost. The results of these 

 three hauls confirmed the Challenger results, and show that 

 fish and invertebrate life is very scanty at depths exceeding 

 2,000 fathoms. The distance to which shoals of edible demersal 

 fish extend downwards from, the continental slope is a question 

 of considerable practical importance, since the great trawl 

 fisheries of Northern Europe are only limited by the ground 

 on which fish of economic value are found in sufficiently large 

 quantities to make trawling a commercial success. If the 

 boundary of the abyssal plain be fixed at 2,000 fathoms, the 

 area between 2,000 and 1,500 fathoms may be considered as a 

 transitional zone between the abyssal plain and the continental 

 shelf. The area between the 1,000 and 2,000 fathom line com- 

 prises ig'3 per cent, of the ocean floor, so it is a by no means 

 negligible area in point of size, seeing that practically^ the 

 whole of the present deep-sea trawling is carried out on an 

 area shallower than 100 fathoms i.e., 7 per cent, of the sea 

 bottom. 



Between 1,500 and 2,000 fathoms the Challenger made 25 

 hauls, the Michael Sars 3. Here the fish and invertebrates 

 are much more abundant, but still in nothing like sufficient 

 numbers to pay commercial trawlers. 



Between 1,000 and 500 fathoms, 3 per cent, of the ocean 

 floor, the number of fish, though relatively more abundant, 

 still only averages about 90 per haul. 



From 100 to 500 fathoms, 5'6 of the ocean floor, edible fish 

 are certainly present in some localities in sufficient abundance 

 to pay commercial trawlers, even when the difficulties and 

 expense of trawling at these great depths are taken into con- 

 sideration. At depths of 500 fathoms the Michael Sars 



3 



