common seal vs sea leopard

common seal

noun
  • Phoca vitulina, a seal living in the northern Atlantic and Pacific oceans. 

sea leopard

noun
  • The harbor seal, Phoca vitulina. 

  • Hydrurga leptonyx, of the Antarctic Ocean 

  • Leptonychotes weddellii, of the Antarctic. 

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