How adaptable are narwhal? A comparison of foraging patterns among the world's three narwhal populations

摘要

How organisms will fare in the face of climate change depends on their behavioral adaptability to changing conditions. Adaptability in foraging behavior will be particularly critical as food web changes are already occurring in Arctic regions. Stomach contents from narwhals (Monodon monoceros ) in the Baffin Bay (BB) population have suggested that narwhals are dietary specialists with little behavioral flexibility, but there are two other narwhal populations in the world, the Northern Hudson Bay (NHB) and East Greenland (EG) populations, of which very little is known about diet. We investigated whether plasticity in foraging behaviors existed among the world's narwhal populations and between sexes by comparing their stable isotope values and niches, and running stable isotope mixing models to determine primary prey. Stable isotope analysis was conducted on skin collected by Inuit hunters during their subsistent narwhal hunt in Canada and Greenland. Stable isotope analysis on carbon (δ~(13)C) and nitrogen (δ~(15)N) revealed the three populations have distinct stable isotope values that are not expected based on geographic differences and that males in all populations had significantly higher δ~(13)C. Stable isotope mixing models revealed narwhals in EG forage more on pelagic prey, particularly capelin, while those in NHB typically forage in the benthos. Males, probably because of their size and enhanced diving ability, likely feed more intensively on benthic organisms, resulting in their higher δ~(13)C. Stable isotopic niches were similar between males and females in each population, and between NHB and BB, but EG narwhals had a significantly larger niche, suggesting they either forage across a larger geographical expanse, or whales within the population employ individual dietary specialization. This is the first study to use stable isotopes to evaluate and compare diet in all three narwhal populations, which is vital for understanding how they will fare in the face of changing climate. We discuss how narwhal are adaptable in their preferred prey and how there is potential for narwhal to adjust foraging behavior in the face of the dramatic ecosystem shifts occurring with climate warming.