The relationship between the humans and the natural world of the sea in The Old Man and the Sea is a mixed relationship, as is the case in real life.
Santiago loves the ocean - the colors, the patterns in the waves, the feel of the salty air. At the same time, he recognizes the power and the potential for danger inherent in that body of water. Santiago feels kinship with some of the animals of the ocean - indeed, he relates closely and with great respect to his great fish.
You are killing me, fish, the old man thought. But you have a right to. Never have I seen a greater, or more beautiful, or a calmer or more noble thing than you, brother.
Of course, he detests the Portuguese man-of-war and the sharks.
Through it all, the old man recognizes his dependence upon the sea for his livelihood. He understands that he has to work hard for what he gets from the ocean, but he also takes pride in his knowledge and his ability to be able to make his living from nature, as a fisherman.
In Hemingway's tale of the struggle of man against the sea, there is the establishment of opposing forces, while at the same time there is a respectful acknowledgement of the puissance of Nature against which man is often powerless.
Despite his prowess as a fisherman, Santiago recognizes the superiority of the sea. At the same time he loves the sea, calling it "la mer" rather than the masculine "el mar" which many other fishermen use to denote their competition with this mighty element of nature. Santiago recognizes that he is a part of nature:
Everything about him was old except his eyes and they were the same color as the sea and were cheerful and undefeated. (Ch.1)
While he catches the marlin and ends his bad luck, Santiago is unable to bring the mighty fish in because sharks eat its flesh. Nevertheless, Santiago brings in the skeleton to prove that he has actually caught something and has interacted with nature.
The Old Man and the Sea is a parable that presents man's relationship with nature. It is a relationship in which man cannot conquer nature, which is more powerful; however, he can become part of it and endure. Santiago loses his battle with the great fish, but he returns to dream of the lions that are a powerful part of nature.