Pacific herring vs herring

Pacific herring

noun
  • A species of the herring family native to north Pacific Ocean from Yellow Sea to Baja California; Clupea pallasii. 

herring

noun
  • A type of small, oily fish of the genus Clupea, often used as food. 

  • Fish in the family Clupeidae. 

  • Fish similar to those in genus Clupea, many of those in the order Clupeiformes. 

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