The kerosene whale
The kerosene whale is the world’s only source of lamp oil. In addition to the highly sought after, and highly flammable, eponymous oil, it provides source material for a wide variety of waxes, preservatives and mordants. Its baleen is used in fashion, in combs and for magicians’ quills, its jawbones make perfect howdah bows for the larger dinosaurs and its eyes, pickled, can be sold at good prices to alchemists. Unsurprisingly it has all but withdrawn from the shores of civilisation: whaling expeditions must now venture far out into the uncharted Sea of Tar to find their prey.
Only fully mature whales have the huge subcutaneous mixed oil deposits that make hunting profitable. Now that kerosene whales have begun traveling in pods up to a score strong, those adults are protected by juveniles who, lacking the large nose-bulbs of their parents, are confident to attack the ships sent after them, sometimes co-ordinating their strikes to capsize large vessels and drag sailors down to the depths in whirlpools.
Whalemen and sages agree that the whales have changed their behaviour because of human hunting. Most dismiss as paranoid raving the suggestion that they are reacting specifically to the use of live kerosene whales as floating bombs in the recent wars. How, they ask, could the whales know? They are, after all, only monsters.
Update: of course the sages could resolve this problem if only they had City of Iron’s whale speech.