Question

how does a trawler man catch fish in deep water

Answer 1

Trawler man uses the net to catch fishes in deep water. They launch a net when a group of fishes flow in their way and ends up caught up in the net. Than they lift up the net and gets fishes stuck in it through which they can not get out. 

Answer 2

A trawler man catch fish in deep water by the principle of echo using the SONAR. SONAR sends sound waves through water which rebounds when they strike the fish, thus after knowing the position of the fish ( position of the fish and the depth in which it is present ) by continuously sending sound waves, the trawler man uses net or similar objects used for fishing to catch the fish from the resultant depth of the water.