"The fish is my friend too,' he said aloud. 'I have never seen or heard of such a fish. But I must kill him.'"
Teddy Roosevelt on safari, 1909 or 1919
Public DomainTeddy Roosevelt on safari, early 1900s

Hilary Hemingway (Ernest Hemingway's niece) and Carlene Brennen discuss this passage in Hemingway in Cuba:

In 1934, Hemingway wrote his friend John Dos Passos, "I am in training to be a naturalist." Now it may be difficult for many to think of Ernest Hemingway as a naturalist or conservationist, since it seemed he never met an animal he didn't want to kill. But back then, being a conservationist--in the tradition of Teddy Roosevelt--meant conserving animals today to have animals to hunt tomorrow. It meant understanding these animals, studying them in their natural habitat, analyzing their migration, feeding habits and physical changes over their life span. Further, it meant sharing that mystical bond between the hunter and the prey, the bond that Ernest wrote of so memorably in The Old Man and the Sea. The character Santiago speaks of his love and admiration for the great fish even as he is determined to kill it.