lake trout vs sea trout

lake trout

noun
  • A large species of trout found in lakes in North America, Salvelinus namaycush. 

  • Whiting fried in batter and served in a sandwich. 

sea trout

noun
  • A fish of the species Salmo trutta morpha trutta, closely related to salmon and a subspecies of brown trout. It is lighter in colour than the brown trout, and lives in salt water, returning to fresh water only to spawn. 

  • The weakfish, Cynoscion regalis 

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