fin whale vs rorqual

fin whale

noun
  • A whale of the rorqual family (Balaenoptera physalus). 

rorqual

noun
  • Any whale of family Balaenopteridae, with longitudinal skin folds running from below the mouth to the navel, allowing the capacity of the mouth to expand greatly when feeding. 

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