Good advice here. I work part time at the National Aquarium in Baltimore, and while I don't work with sharks, I work with rays, skates and other animals that can be picky eaters. If an animal is being picky, we try basically everything we have until we find something they want to eat.
Last picky animal I had to try to get to eat was a half-blind sea bass. We attempted to pole feed everything we had. We did scallops, crab meat, squid, mackerel and smelt. He refused to eat it all. He did finally settle on shrimp. They're not the most nutritious, but he's at least eating.
I would get an array of fresh seafoods from the grocery store and see if you can entice it with anything. Get a feeding stick and try to dangle it in front of the shark's face in a life-like manner. When choosing seafoods, be careful of those with relatively high copper (
check Randy's article here, table 1 to be precise). If it still won't eat, look into live foods.