In The Old Man and the Sea, what is the relationship between the old man and his hooks?

Santiago has a working relationship with his hooks. Mostly, they are utilitarian and a cause for joy when he succeeds in catching a good haul. He uses them to get food in more than one way; at one point he snags a bunch of Gulf weed with a hook to eat the shrimps inside. 

Sometimes, Santiago sees his hooks as cruel. He caught a female marlin with Manolin once as its mate watched. Both Manolin and he felt terrible, but still caught and kept the fish. 

He remembered the time he had hooked one of a pair of marlin. The male fish always let the female fish feed first and the hooked fish, the female, made a wild, panic-stricken, despairing fight that soon exhausted her, and all the time the male had stayed with her...That was the saddest thing I ever saw with them, the old man thought. The boy was sad too and we begged her pardon and butchered her promptly.

Santiago's hooks are a tool he is extremely in tune with. He can tell what type of fish is on the other end of the hook just by touching the line and feeling the movement and pull. Later, his line turns against him when his hand begins to cramp and he has tremendous trouble handling the huge marlin he hooked.

The hooks are covered with bait, so a fish cannot see or feel even a single part of the hook. 

Each bait... was covered with fresh sardines... There was no part of the hook that a great fish could feel which was not sweet smelling and good tasting.

Santiago sees the hooks as a trick to fool the fish into thinking they are getting a sweet treat when really he has their death on his mind.

He felt the light delicate pulling and then a harder pull when a sardine’s head must have been more difficult to break from the hook. Then there was nothing. “Eat it a little more,” he said. “Eat it well.” Eat it so that the point of the hook goes into your heart and kills you, he thought. Come up easy and let me put the harpoon into you. All right. Are you ready? Have you been long enough at table?

Ultimately, Santiago's hooks turn against him again at the end of his journey. He wishes he had never left the house that morning three days ago, and never hooked this fish. By hooking the fish, he tied their destinies together, literally by tying the fish via the hook to the boat during the struggle, and figuratively by entwining their lives.