I'm still convinced its Quin's horn that we have heard precious little about. My guess, after the sea monsters started dying, she lost the horn somehow, and hid the loss in some manner and was able to keep a massive uproar from happening by using everyone's fear of her.
Who knows, maybe she lost the horn before the sea monsters started dying, and she hunted them down to eliminate the theory of its disappearance with probable explanation, or the sea monsters could have just moved back to wherever THEY call home after the horn was lost, and no one has seen them since.
I don't know, I just want to see a quest line that takes us into the eastern Lands, and if I get my hands on that horn, I will be very happy. *imagines riding into battle atop a massive whale shark and other strange beasts.*
"We call it being a hero"
"That's interesting, we call it utter stupidity"