Narwhals are small whales that live in cold waters.
Small in size for whales, narwhals swim in cold waters and are about twelve feet long. Most notably, male narwhals sport a long spiraled, twisting tusk consisting of one of their teeth. Powerful swimmers, narwhals can reach quick speeds in the water.
A pod of narwhals constantly followed the ice ship of the seafaring ape Gutt, who threw any malcontents into the waters for the narwhals to dispose of. They were completely subservient to Gutt, swimming to him when he whistled out to them, pushing his ship when needed, and even acting as steeds at one point.
What became of them after Gutt's defeat is currently unknown, if Gutt survived his encounter with sirens he could've been reunited with them as he would need something to sail away with, if he's truly dead then they could've simply continue to swim in the waters maybe someday finding a new master.