Why do Narwhals have tusks?

Narwhals, the unicorns of the sea, have large tusks (which are actually large canine teeth) protruding from their foreheads. Each tusk holds 10 million nerve endings. But what do they do? Narwhals have not been observed fencing with them for territory, food or mates, or using them to cut things or defend against enemies. Scientists think they may be sensors, sensing changes in pressure, salinity and water chemistry. I’ve just been reading “Where’s Mr Narwhal?” to my 1-year-old, and it occurred..