trawling vs trolling

trawling

noun
  • A commercial fishing technique in which a net is dragged by a moving boat. Not to be confused with trolling, which drags (one or more) lines. 

  • A laborious search. 

trolling

noun
  • A fishing technique in which one or more baited fishing lines are dragged by a moving boat. Not to be confused with trawling, which drags a net. 

  • The act of one who trolls (in various senses). 

How often have the words trawling and trolling occurred in a corpus of books? (source: Google Ngram Viewer )