Trophic Levels of North Pacific Humpback Whales (Megaptera novaeangliae) Through Analysis of Stable Isotopes: Implications on Prey and Resource Quality

Trophic levels of 1,105 humpback whales from six geographically and isotopically distinct North Pacific feeding groups were calculated using delta N-15 of humpback whales and regional primary consumers. The overall mean trophic level for North Pacific humpback whales was 3.6 +/- 0.02, indicating a diet of both fish and zooplankton, and, thus, supporting assumptions of humpback whales as generalist predators. The highest mean trophic level was calculated for the north Gulf of Alaska group (4.0 +/- 0.03), while the lowest was found for the Russian and the western Aleutian Islands group (3.3 +/- 0.08). Differences in mean trophic levels suggest that feeding groups differ in the proportion of fish and zooplankton in their diets.