While on a small outer cay (cays are small coral islands-- pronounced keys -- as in Florida Keys), I came upon a shark trotline. Someone was fishing for shark. A trotline is a passive way to fish. The very large hook is attached to a three foot piece of cable which is attached to a chain and securely fastened to shore.
The hook is baited with an inedible fish or a piece of meat. The bait is wired to the hook with picture frame wire to keep it in place. The whole thing is chucked into the ocean and the area is chummed. Chumming involves getting fish guts, blood and heads all steeped in oil and left to marinate. Then it is dumped in the ocean around the baited hook. The smell attracts sharks.
The shark can be a nocturnal creature, and this is set out in the evening. The line is checked in the morning and the shark is hauled in. Shark steaks are popular, and the fins are sold to Asian buyers who pay a premium for the main ingredient of shark fin soup which is a delicacy.
Judging by the shape of this trotline rig, it hadn't been used in at least a year.