northern pike vs pickerel

northern pike

noun

  • A species of pike, Esox lucius. 

pickerel

noun

  • A freshwater fish of the genus Esox. 

  • Walleye, A species of gamefish, Sander vitreus, native to the Northern U.S. and Canada with pale, reflective eyes. 

  • A wading bird, the dunlin. 

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