The Nautshval or Nauthvalur, which translate as cow-whale or ox-whale, is one of the many evil whales of Icelandic folklore. This particular one, the second biggest of them, will show up if its name is said out loud.
The nautshval is a toothed whale. It has a face with large nose with two big rounded nostrils that work as a fog horn. Male nautshval have large heads, that like in bulls, present a type of horn, in this case two long nodules. Some has described this whale as having a wormlike body, others said that instead of fins it has long appendixes resembling legs. Most agree, however, that the nautshval name was given not because of its appearance, but for the terrifying bull-like bellow it makes when hungry, a sound like the loud buffing of a maddened bull.
Nautshvals never swim near the coast, but their call reverberates over long distances. When it reaches land, its vibrations shake the ground. For those unfortunate enough to be out at sea when the nautshval calls, the sound may knock the oars out of their hands or make a boat's hull crack. Going out to sea is forbidden if the nautshval bellowing has been recently heard.
As will all evil whales, the nautshval delights in killing people and scuttling smaller boats, but it has a particular fondness for beef. The whales are attracted to cattle on board ship. It is said, that in the waters out of Grimsey, one nautshval harassed a small vessel until they released the one cow on board. The animal promptly dove into the sea; the bellow of a nautshval is hypnotic to cattle. It compels them to run off cliffs and headlong into the sea. After the Grimsey incident, cattle had to be locked up for days until the nautshval spell wore off. Hence, cow-herding was strongly discouraged in areas where nautshvals had been heard. At times, out of desperation, small coastal communities sacrificed one bull or cow to satisfy the nautshval hunger, making it safe to go out to sea again.
Hunting nautshvals was a nearly impossible and highly risky endeavor, and little was gain by trying. Like it's the case with all evil whales, the meat of this monster is uneatable, so few were the intrepid souls who ever dare go after a nautshval.
-Davidsson, O. 1900 The Folk-lore of Icelandic Fishes. The Scottish Review, October, pp. 312-332.
-Hlidberg, J. B. and Aegisson, S.; McQueen, F. J. M. and Kjartansson, R., trans. 2011 Meeting with Monsters. JPV utgafa, Reykjavik.