The waters around Requiem Island (Now Starswirl's school) were long thought to be uninhabited, emptied of anything but fish and shells nearly a century ago- it appears from student's interactions and curiosity that perhaps it wasn't so devoid of creatures after all.
Feverfew Historical Society Records
Legends going back centuries tell tales of great sea monsters that roamed the coast of Feverfew- but upon further inspection of town records, it seems that there is no clear evidence for the 'Feverfew Monster' save for tall tales told by sailors. On the other hoof- there are plenty of records of seaponies.
Feverfew once enjoyed a healthy relationship with seaponies who stopped by the town for trade- and one of the town's most notable figures, Penned Paper, was a runecarver taught by a seapony. In the early 1700s, a trade outpost, Clef-Point, was established off the coast for traveling merfolk to stop in, and rest before heading to the docks of Feverfew to sell their wares to those on the surface. Trade boomed until around the early 1810's when visits began to die down until a final visit was made from the then-leader of the trading outpost, Pearl Crest. The mermares were leaving, headed off to a new outpost in Tessitura instead.
Little record exists as to why they left, nor are there many ponies in the village who remember when the sea-ponies were here to begin with. Aside from those in the Historical Society, most of Feverfew carries on blissfully unaware that anything at all lurks the waters save for hauls of fish. Sometimes, boats go missing out at sea- but those are the dangers of sailing, right? Who knows, maybe the Feverfew monster is real after all.