| Summary: | Humpback whales Megaptera novaeangliae in the North Pacific Ocean are a migratory species known to have a complex population structure on both feeding and breeding grounds. We described the structure of this population using stable isotope analysis of skin samples (n = 1105) collected from free-ranging North Pacific humpback whales from 10 sampling regions in 2004 and 2005. We detected significant quadratic relationships between latitude and both delta C-13 (R-2 = 0.29) and delta N-15 (R-2 = 0.23) as well as between longitude and delta C-13 (R-2 = 0.43) and delta N-15 (R-2 = 0.16). A weak negative linear relationship was seen between increasing distance from shore and both delta C-13 (R-2 = 0.05) and delta N-15 (R-2 = 0.02). Sampling regions were significantly different for both delta C-13 (ANOVA, F-9.1094 = 136.4, p < 0.001.) and delta N-15 (F-9.1095 = 71.5, p < 0.001). We performed classification tree analyses using delta C-13 and delta N-15 as predictor variables to assign membership to sampling regions, Results of initial classification and ANOVAs supported combining the 10 sampling regions into 6 feeding groups. When applied to these feeding groups, the classification tree was able to predict 57% of group membership correctly, with accuracy rates for individual groups ranging from a low of 19% to a high of 78%. These results indicate that stable isotope analysis can be used to distinguish unique feeding aggregations of humpback whales within the North Pacific Ocean. Ultimately, isotopic characteristics of these aggregations can be applied to animals sampled on breeding grounds to assign them to a feeding aggregation, enhancing the ability to describe habitat linkages and migration patterns of humpback whales.
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