# Impact of Tusk Anomalies on the Long‐Term Foraging Ecology of Narwhals

## TL;DR

The study finds that common tusk anomalies in narwhals do not affect their long-term foraging habits, but rare dental oddities may lead to different diets.

## Contribution

This is the first study to use stable isotope analysis and genetic sexing to assess the foraging ecology of narwhals with tusk anomalies.

## Key findings

- Most two-tusked males and one-tusked females had stable isotope values within normal ranges.
- Rare dental anomalies were associated with isotope values outside the typical narwhal range, suggesting different diets.
- Common tusk anomalies appear to have limited ecological consequences.

## Abstract

Male narwhals are unique in having a long, spiralled tusk, while females of the species do not have a tusk. However, a small number of individuals develop tusk anomalies, including two‐tusked males or females with a tusk. In this study, we combine genetic sexing and bone collagen stable isotope (δ
13C and δ
15N) analysis to evaluate whether these tooth anomalies impact long‐term foraging ecology. Our analysis of individuals collected in the waters around Greenland showed no systematic impacts; eight of nine two‐tusked male narwhals and all three one‐tusked female narwhals fell within the normal range of known isotopic diversity from their source geographic regions. Two specimens with other forms of unusual dentition both showed stable isotope values outside the range of narwhals, suggesting that their diets were different. Therefore, the most common tusk anomalies in narwhals appear to have limited ecological consequences, while rarer forms of dentition are likely associated with altered foraging ecology.

We combined stable δ13C and δ15N isotope analysis and genetic sexing to investigate whether narwhals with dental anomalies have a distinct long‐term foraging ecology. Our results showed no difference in stable isotope signature of two‐tusked male and one‐tusked female narwhals relative to normal‐tusked narwhals, indicating that an extra tusk does not impact narwhal foraging ecology. Two specimens with other odd dentition both showed stable isotope values far outside the range of narwhals, suggesting their diet was different.