They change color as they age

When narwhals are young, their color changes to a bluish-black hue from their birth color of white or light gray. Their skin tone darkens and grows more mottled with age before lightening once more as they get older (older narwhals are almost completely white). Researchers can identify and study baby narwhals in the wild using the color variations, thanks to this color change.

Despite living in one of the most hazardous environments on Earth, narwhals are thought to be among the longest-lived marine mammals, with an average lifespan of 50 years. To demonstrate this, scientists examined chemical changes in the eyes of 75 dead narwhals discovered in Greenland between 1993 and 2004. They found that 20% of the whales were over 50 years old, with the oldest whale being a female who was thought to be between 105 and 125 years old.