northern fur seal vs sea lion

northern fur seal

noun
  • A fur seal of the species Callorhinus ursinus (formerly Arctocephalus ursinus), of the northern Pacific. 

sea lion

noun
  • A marine mammal of any of several genera in the family Otariidae (the eared seals). 

  • A steamer transporting cattle from the ports of Texas. 

  • A monster consisting of the upper part of a lion combined with the tail of a fish. 

  • A cow or bull transported by steamer from the ports of Texas. 

How often have the words northern fur seal and sea lion occurred in a corpus of books? (source: Google Ngram Viewer )