Dear MARMAM community, On behalf of my co-authors, I am pleased to share our latest open-access publication: "Drone photogrammetry reveals age-structure shifts with potential consequences for the viability of spinner dolphins in Hawai'i", published in *Endangered Species Research *and available here: https://www.int-res.com/journals/esr/articles/esr01512 <https://www.int-res.com/journals/esr/articles/esr01512> Feel free to reach out if you have any questions or problems accessing the link (fvivier@hawaii.edu or fabien.vivier@univ-lr.fr). Kind regards, Fabien Vivier - Postdoctoral Research Fellow *La Rochelle Université - Observatoire Pelagis* *UAR 3462 CNRS-LRUniv* *5 allée de l'océan* *17000 La Rochelle* *France* -------------------------------------------------------------------- *Abstract:* Evaluating age structure in long-lived species is crucial for understanding population dynamics. In mammal populations, the proportion of calves, juveniles, and adults serves as an early indicator of population trajectory, where stability usually reflects viability, and deviations may signal growth or decline. Surveys conducted in 2021 and 2022 integrated unoccupied aerial system (UAS, drone) photogrammetry to assess the age structure of the Hawai'i Island population of Gray’s spinner dolphins *Stenella longirostris longirostris* chronically exposed to human disturbances for over 4 decades. Age-length data from stranded dolphins allowed us to estimate total body length (TL) of dolphins from photographs using the relationship between TL and blowhole-to-dorsal-fin distance and to develop the first age-length growth curve for this population. We then used TL estimates to classify dolphins as calves (0-2 yr), juveniles (≥2-9 yr), or adults (9+ yr). Calves comprised only 9.3% of the population, significantly lower than the 17.2% expected under stable conditions for spinner dolphins and below values reported for bottlenose dolphins Tursiops spp. (12.4-18%). This suggests limited recruitment, raising concerns about long-term viability. Sampling and ecological factors (e.g. prey availability) did not explain the low calf percentage, suggesting that other factors, such as chronic anthropogenic disturbances like tourism, are likely affecting the reproductive rates of this population. These findings support the need for effective management interventions, such as time-area closures in critical dolphin resting habitats, which may help mitigate disturbances. Long-term monitoring of this population is needed to evaluate trends in age structure and abundance and the efficacy of management interventions. *How to cite this paper:* Vivier F, Lusseau D, Hofmann NJ, West K, McPherson L, Nemeth C, Wells RS, van Aswegen M, Manlik O, Chivers S, Pacini A, Booth C, Bejder L (2026) Drone photogrammetry reveals age-structure shifts with potential consequences for the viability of spinner dolphins in Hawai'i. Endang Species Res 60:esr01512 https://doi.org/10.3354/esr01512 *Funding:* NOAA-PIFSC, the Office of Naval Research, Dolphin Quest, the US Department of Defense’s Defense University Research Instrumentation Program, the Omidyar Ohana Fund, the NOAA National Marine Fisheries Service (NMFS) John H. Prescott Marine Mammal Rescue Assistance Grant program, Earthwatch Institute, and Brookfield Zoo Chicago.