Encrusted Tail Fin

Encrusted Tail Fin is a quest item only lootable by players on the quest. These fins are strong and resistant to corrosion from salt, which is why they have become much sought-after by the racers of Mirage Raceway on the Shimmering Flats.

Source
Encrusted Tail Fins can be looted from the elite Saltscale murlocs off the west coast of northern Stranglethorn Vale, almost directly west of Grom'gol Base Camp, deep underwater in the area known as the Vile Reef.