Tracing migratory movements of breeding North Pacific humpback whales using stable isotope analysis



B. H. Witteveen; G. A. J. Worthy;J. D. Roth


North Pacific humpback whales Megaptera novaeangliae are migratory animals with a complex population structure, segregating into geographically distinct aggregations on high-latitude feeding grounds. Several feeding aggregations may converge on a common breeding ground for mating and calving. Understanding how feeding and breeding habitats are linked is critical to understanding humpback whale life history and addressing management and conservation efforts. In a continued effort to explore the population structure of North Pacific humpback whales through the analysis of stable carbon (delta C-13) and nitrogen (delta N-15), the present study extends on a previous study of feeding animals to describe migratory linkages to breeding grounds (Witteveen et al. 2009). Skin samples (n = 597) collected from 4 known breeding regions were analyzed for delta C-13 and delta N-15. Breeding regions differed in both delta C-13 (F-3,F-585 = 62.3, p < 0.001) and delta N-15 (F-3,F-585 = 37.2, p < 0.001). Breeding values reflected the foraging locations for 46 ind. sampled on both habitats; the relationship between the breeding and feeding stable isotope ratios was significant and positive for both delta C-13 (F-1,F-44 = 10.3, r(2) = 0.19, p = 0.002) and delta N-15 (F-1,F-14 = 40.9, r(2) = 0.48, p < 0.001). Furthermore, individual breeding and feeding values did not differ for delta N-15 (t(45) = 1.41, p = 0,17) or delta C-13 (t(45) = -1.15, p = 0.26) in pairwise comparisons. We used delta C-13 and delta N-15 in a classification tree analysis to describe probable migratory linkages to 6 previously described feeding groups. Stable isotope ratios predicted regional patterns of movement, and assignments of breeding individuals to feeding grounds differed by 12% on average from photographic matching. Our results indicate this technique can be used to help understand the population structure and ecology of North Pacific humpback whale populations, especially when used in combination with other research techniques.

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Marine Ecology Progress Series



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