Baleen isotope records show niche contraction during UME years; juveniles may be more affected

Geraldine Busquet presented stable‑isotope results from baleen plates drilled at segment resolution (each centimeter ≈ 15–22 days), comparing whales that died during UME years with those from non‑UME periods. She reported high inter‑individual variability in both δ15N and δ13C across a 40‑year plate series but found that, at the group level, isotopic niche area contracted during UME periods. "There is definitely an isotopic niche contraction during UME events although there is a high overlap among both periods," Busquet said.

Busquet explained potential interpretations: niche contraction may reflect reduced variability in resource use, increased use of more coastal feeding habitats (higher δ13C), or physiological changes (nutritional stress can alter δ15N). She noted juveniles' niche contraction was driven by both nitrogen and carbon and suggested juveniles may be more vulnerable or show stronger physiological signals. The team plans amino‑acid specific isotope analysis to help separate dietary shifts from physiological effects recorded in baleen.

Limitations Busquet flagged include baseline spatial/temporal variation in isotopic baselines, high inter‑individual variation that complicates inference, and the labor intensity of processing baleen plates. She called for more plates (the project has collected 64 plates and processed 27 to date) and for integrated modeling that combines baleen records with cataloging, body condition and necropsy data.