With the old man being alone on the sea and all, a lot of characterization of animals is done, not of people. And a great tool for such characterization is the use of personification. The old man talks about jellyfish, turtles, birds, and most importantly, the marlin, as if they were people. He gives them thought processes, even personalities. And all of his comments on the animals tell us more about him, which counts as a characterization tool in its own right, which is kind of nifty.
Hemingway doesn’t beat around the bush. How do we know the old man is proud? Because he says that the old man suffered "no loss of true pride." How do we know Manolin loves Santiago? Because he says "the boy loved him."
We get some pretty intense descriptions of the old man’s gaunt, emaciated body. Hemingway never lets us forget the one key fact that this guy is old and not in top-notch fish-fighting condition. That, of course, makes him that much more impressive for winning the battle against the marlin. So, oddly enough, the description of the old man’s physical shortcomings serves to highlight his strengths.
Yes, the old man talks to himself. No, he isn’t crazy. And in case you don’t believe us, he tells you that himself. He just doesn’t have a radio or a newspaper or an iPhone, so he finds companionship in himself and in the creatures around him. This reminds us that the old man is "strange," in the sense of individuality, and that he is forced to do his battle in isolation from others.