In collaboration with the University of New Mexico, this project combines stable isotope analysis of blue, fin, and humpback whale skin biopsy samples collected by the WHET Lab between 2004 and 2019 with associated satellite tagging data. The objective is to compare the foraging ecology of these three baleen whale species in the California Current Ecosystem, and to gain a better understanding of how they partition their resources and habitat. The three species feed on krill in this region, and humpback and fin whales are also known to feed on small pelagic fish. Stable isotope concentrations of nitrogen (δ15N) and carbon (δ13C) in the base of the food web vary regionally, leading to gradients in baseline values that are reflected in whale tissues and that can provide information about their diet (trophic level and composition) and where they fed previously.
We have a total of 210 skin samples comprising of 106 blue, 17 fin, 86 humpback, and one blue-fin hybrid whale. By comparing the standard ellipse areas (SEA) based on δ13C and δ15N values, we are assessing the isotopic niche of the three species in terms of relative size and overlap. Humpback whales had the largest SEA, with the most overlap between blue and fin whales and the least overlap between humpback and fin whales (Figure 1). These results can be interpreted in terms of similarities or differences in diet or habitat use between the species, based on regional baseline isotopic values of past feeding grounds.
Liam Mueller-Brennan is a Master’s student on the project. His thesis focuses on the humpback whale samples, with the goal of gaining ecological insight into their population structure in the North Pacific Ocean as revealed by stable isotope and satellite tagging data. He recently presented a paper at the annual meeting of the Scientific Committee of the International Whaling Commission, titled “A preliminary analysis of stable isotope data from satellite tagged humpback whales in the North Pacific.” Liam also presented this work as a poster at the annual Society for Marine Mammalogy Northwest Student Chapter Meeting.