Research Document - 2010/134

Stable isotope and fatty acid analyses of samples from entrapped narwhals (Monodon monoceros)

By C.A. Watt and S.H. Ferguson

Abstract

Narwhals (Monodon monoceros) are medium sized odontocetes that live exclusively in Arctic waters. They are considered the most vulnerable Arctic cetacean based on their limited distribution, specialized physiological adaptation, and restricted diet which together limit their ability to modify behaviour in the face of changing climate. As a result of changes in seasonal ice characteristics associated with climate change and the limited ability of narwhal for behavioural modification, ice entrapment events may become more prevalent. In November 2008, an ice entrapment event occurred off the coast of Bylot Island, Nunavut near the community of Pond Inlet. Hundreds of narwhals attempted to travel outside of the inlets and fjords in the area before becoming entrapped by thickening ice. As a result, a humane Inuit harvest of animals occurred before the whales drowned. In total, 250 skin and blubber samples were collected from over 600 harvested whales. The entrapment event provided a unique sample because the individuals were likely closely related and many were females trapped with their young, whereas typically samples obtained from Inuit subsistence hunts are biased towards males. A dietary study was initiated to determine if diet differed among age classes and between sexes, and to determine if diet could be utilized to elucidate social structure in narwhals. Skin samples were analyzed for stable isotopes of carbon and nitrogen, which provides information on foraging location and trophic level, and dietary fatty acids in blubber, were used to identify primary prey items. Non-parametric statistics identified differences in isotopic signatures among age classes of narwhals, but no difference between sexes. Principal component analysis of fatty acids resulting from dietary intake qualitatively assessed feeding ecology of narwhals and determined there were no dietary differences between sexes or among age classes; however, distinct feeding groups were evident and genetic work is underway to determine the relatedness among these groupings. Emaciation appeared to have no significant impact on the fatty acid or isotopic signatures of samples from the entrapment event compared to published results, although more work is required to validate these conclusions.

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