Take the Sea Creature Bones to Gwennyth Bly'Leggonde in Auberdine.
The remains of what appear to be a giant thresher have washed ashore on the rocky inlet of the Twilight Shore. The thresher is several times larger than any of the other threshers spotted in these parts. Wherever it came from, this creature would not seem to have been native to Darkshore.
Though the creature has been picked apart in places, enough of it remains to gather a suitable sample for Gwennyth Bly'Leggonde in Auberdine.