Calcium Isotopes Correlate With Baleen Whale Feeding Ecology

Baleen whales are among the largest animals ever and engineer marine ecosystems by transporting nutrients both vertically through the water column and across vast oceanic distances. Hidden underwater, their feeding habits often remain unseen and hence must be studied indirectly based on stomach contents and stable isotopes. Here, we explore the potential of bone‐bound calcium isotopes as a chemical proxy for extant baleen whale foraging ecology. Unlike bulk nitrogen and various trace elements (Mg, Sr, and Ba), calcium isotopes clearly distinguish gulp ( n = 4 species) from skim feeders ( n = 4 species) and provide a powerful tool to infer diet and feeding strategies. The difference in calcium isotope composition plausibly reflects incidental ingestion of seawater, which may be more pronounced in skim feeding whales than previously thought.