Research Document - 2012/057

Using stable isotope analysis as a tool for narwhal (Monodon monoceros) stock delineation

By C.A. Watt, S.H. Ferguson, A. Fisk, and M.P. Heide-Jørgensen

Abstract

Stable isotope analysis of carbon and nitrogen was conducted on narwhal skin tissues from nine hunting areas, which included six narwhal stocks in the Canadian Arctic and Greenland: Somerset Island, Eclipse Sound, Admiralty Inlet, and East Baffin Island from the Canadian Arctic, and Melville Bay, and West Greenland from Greenland. Samples were also obtained from narwhals from the Northern Hudson Bay and East Greenland populations, and the High Arctic hunting area in Canada. Discriminant analysis, which included all six stocks, the two populations, and the High Arctic, determined if hunting areas had significantly different isotope values; however, since diet may vary seasonally and by sex, analyses that considered samples divided by the season of collection and discrimination for males and females separately was also conducted. Narwhals from East Greenland and Northern Hudson Bay are genetically and spatially segregated from the Baffin Bay stocks, and these two populations had isotope values that clearly distinguished them in spring and summer. Baffin Bay stocks were more difficult to distinguish; however, there was a significant difference between the Admiralty Inlet and Eclipse Sound stocks in the spring and summer models, and in the model that included all hunting areas regardless of season. There was also a significant difference between the West Greenland and Melville Bay stocks in winter and the Eclipse Sound and West Greenland stocks in autumn. When the model that included all hunting areas was compared to that which considered males and females independently, there was some overlap with the Melville Bay and West Greenland stocks for the females not seen in the model that combined males and females, but the discrimination among males was not significantly different from this model. The results are interpreted assuming both a short (two to three month) and long (one to two years) turnover rate. Overall, stable isotope analysis may be useful for delineating stocks, especially if used in combination with other techniques currently used for stock assignment.

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