Dear colleagues, My co-authors and I are pleased to share with you our recent publication describing the longitudinal hormonal patterns and stable isotope variation in gray whale baleen prior to their death. You can access this publication here: Link to the publication <https://www.sciencedirect.com/science/article/pii/S0016648024000522?dgcid=author> Additionally, we have prepared a blog post detailing the study, which you can find here. <https://blogs.oregonstate.edu/gemmlab/2024/04/15/baleen-analyses-reveals-patterns-in-foraging-ecology-and-stress-physiology-in-gray-whales-prior-to-death/> *Abstract:* *"Individual-level assessments of wild animal health, vital rates, and foraging ecology are critical for understanding population-wide impacts of exposure to stressors. Large whales face multiple stressors, including, but not limited to, ocean noise, pollution, and ship strikes. Because baleen is a continuously growing keratinized structure, serial extraction, and quantification of hormones and stable isotopes along the length of baleen provide a historical record of whale physiology and foraging ecology. Furthermore, baleen analysis enables the investigation of dead specimens, even decades later, allowing comparisons between historic and modern populations. Here, we examined baleen of five sub-adult gray whales and observed distinct patterns of oscillations in δ15N values along the length of their baleen plates which enabled estimation of baleen growth rates and differentiation of isotopic niche widths of the whales during wintering and summer foraging. In contrast, no regular patterns were apparent in δ13C values. Prolonged elevation of cortisol in four individuals before death indicates that chronic stress may have impacted their health and survival. Triiodothyronine (T3) increased over months in the whales with unknown causes of death, simultaneous with elevations in cortisol, but both hormones remained stable in the one case of acute death attributed to killer whale predation. This parallel elevation of cortisol and T3 challenges the classic understanding of their interaction and might relate to increased energetic demands during exposure to stressors. Reproductive hormone profiles in subadults did not show cyclical trends, suggesting they had not yet reached sexual maturity. This study highlights the potential of baleen analysis to retrospectively assess gray whales' physiological status, exposure to stressors, reproductive status, and foraging ecology in the months or years leading up to their death, which can be a useful tool for conservation diagnostics to mitigate unusual mortality events."* -- *Alejandro Fernandez Ajó, PhD* Researcher / Instituto de Conservación de Ballenas <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fballenas.org.ar%2F&data=05%7C02%7Calejandro.fernandezajo%40oregonstate.edu%7Cd188c4131f524c8f128708dc20fb3172%7Cce6d05e13c5e4d6287a84c4a2713c113%7C0%7C0%7C638421510457387410%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=yNan%2B0DNmZT%2BjiIeFSm%2FrdhJE0XaNL3ffp3nAi0Ab%2F8%3D&reserved=0> (ICB, Whale Conservation Institute / Argentina) Postdoctoral Scholar / Marine Mammal Institute <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmmi.oregonstate.edu%2Fpeople%2Falejandro-fern%25C3%25A1ndez-aj%25C3%25B3&data=05%7C02%7Calejandro.fernandezajo%40oregonstate.edu%7Cd188c4131f524c8f128708dc20fb3172%7Cce6d05e13c5e4d6287a84c4a2713c113%7C0%7C0%7C638421510457393979%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=jBz1hUmOOzG7LVXBDBE1gez9GeLqNlhfT%2FJbxEliBeY%3D&reserved=0> | Dept. of Fisheries, Wildlife, & Conservation Sciences Oregon State University Pronouns: he, him, his *fernaale@oregonstate.edu <fernaale@oregonstate.edu>*