mackinaw trout vs steelhead

mackinaw trout

noun

  • The lake trout or North American lake trout, Salvelinus namaycush. 

steelhead

noun

  • The anadromous form of the rainbow trout, Oncorhynchus mykiss. 

  • The ruddy duck. 

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