Silver Hook

Source
This item drops from:
 * Basking Shark in Deeprun Tram
 * Reef Shark in Ashenvale
 * Hammerhead Shark in Wetlands
 * Coral Shark in Dustwallow Marsh
 * Whitetail Frenzy in Ghostlands
 * Mammoth Shark in Azshara
 * Great Shark in Tanaris

It can also be found in a Barrel of Fish.

Apparently, a silver hook is preferred when catching sharks. Who knew?