The narwhal is often referred to as the “unicorn of the sea.” The creature has long fascinated scientists and the public alike with its iconic spiraling tusk. However, recent research reveals that these tusks are not just ornamental; they serve as invaluable biological records.
Just like tree rings can tell us about environmental conditions, the growth rings in a narwhal’s tusk can shed light on the animal’s diet and the changes in its environment.
Studying Narwhal Tusks
An international team of scientists conducted a study by examining ten narwhal tusks obtained from Inuit hunters in northwest Greenland. The tusks, which are actually elongated canine teeth found only in males, were cut in half lengthwise to reveal their growth rings. Each ring represented one year in the life of the narwhal. By analyzing these rings, scientists could gain a unique window into the life history of these Arctic mammals.
Scientists discovered that narwhals’ diets have changed in response to the environmental changes in the Arctic. This change is partly due to the shrinking of sea ice.
They measured levels of mercury, as well as stable isotopes of carbon and nitrogen within each ring. Doing so helped them decipher the types of prey the narwhals had consumed in different years. These markers provided a snapshot of the narwhals’ diets and indicated how high their prey sat on the food chain.
The Narwhal Diet
The researchers found that until the 1990s, when the ice cover in the Arctic was still “extensive but varying,” narwhals primarily fed on sea-ice-adjacent prey like halibut and Arctic cod. However, as the ice cover started to decline between 1990 and 2000, narwhals began to consume more open ocean species. These included such species as capelin and polar cod.
These open ocean species sit lower on the food chain. This was reflected in lower mercury levels in the tusk layers for those particular years.
What’s concerning is that even though narwhals’ diets remained relatively consistent after the year 2000, mercury levels in their tusks started to rise significantly. This increase is thought to be linked to increased coal combustion emissions from southeast Asia. This revelation raises concerns about how pollutants from human activities are affecting even the most remote ecosystems on Earth.
Prof. Rune Dietz of Denmark’s Aarhus University pointed out that tusks in museums around the world represent an untapped data bank. An analysis of these could provide critical insights into how narwhals have adapted to changes over different periods and in different regions. This could lay the foundation for assessing how they are likely to cope with ongoing environmental shifts.
What We Can Learn
This study underscores the importance of understanding how climate change and human activities are affecting marine ecosystems. It shows how even seemingly unrelated things—like coal combustion in one part of the world—can have a ripple effect that impacts the diet and health of animals living in a completely different region.
Narwhal tusks serve as natural archives. They can reveal the complex interplay between marine biology, environmental change, and even global industrial activities. And they’re helping researchers stitch together a more complete understanding of the Arctic ecosystem.