Impact of Tusk Anomalies on the Long-Term Foraging Ecology of Narwhals

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.