Dear MarMam Community, We are excited to share the following publications first authored by graduate students at the University of San Francisco. The first article, featured in Aquatic Mammals, pertains to the muscle physiology of Arctic seals. The second article, featured in Endangered Species Research, reports the foraging ecology of southern sea otters at their northern range extent in California. Both articles are fully open access and links are provided after each abstract below. *Title: ** Comparative muscle physiology of ringed (Pusa hispida), bearded (Erignathus barbatus), and spotted (Phoca largha) seals from the Bering and Chukchi Seas* *Authors*: Mariah L. Tengler, Jennifer Dearolf, Anna L. Bryan, Colleen Reichmuth, Nicole M. Thometz *Abstract*: The physiological properties of marine mammal skeletal muscle are foundational in defining diving and foraging capacities. Further, these parameters can be useful when assessing the behavioral flexibility of species faced with environmental change or disturbance. Herein, we define species- and age-specific muscle physiology for three ice-associated seal species experiencing Arctic warming. Specifically, we evaluated myoglobin content ([Mb]), nonbicarbonate buffering capacity (β), and fiber type profiles of a major locomotor muscle, the longissimus dorsi. Muscle samples were obtained from subsistence harvested ringed (*Pusa hispida*; *n* = 11), bearded (*Erignathus barbatus*; *n* = 41), and spotted (*Phoca largha*; *n* = 12) seals of all ages in the Bering and Chukchi Seas. Adult ringed seals had the highest [Mb] (6.67 ± 0.20 g 100 g wet tissue-1), followed by spotted (5.38 ± 0.29 g 100 g wet tissue-1) and bearded (4.55 ± 0.07 g 100 g wet tissue-1) seals. [Mb] increased with age for all species, but rates of increase differed by species. In contrast, β was similar for all species and age classes. We documented higher proportions of fast-twitch relative to slow-twitch fibers in these species, and fiber type proportions did not differ significantly with age. Adult bearded seals exhibited the greatest proportion of fast-twitch fibers (68.7 ± 1.5%), followed by ringed (59.0 ± 4.8%) and spotted (55.1 ± 2.1%) seals. Overall, our data suggest a strong link between muscle physiology, diving behavior, and life history strategies, and provide insight into the physiological capacities of these potentially vulnerable species. *Link to Article*: https://www.aquaticmammalsjournal.org/article/comparative-muscle-physiology-... *Title: **Foraging ecology of southern sea otters at the northern range extent informs regional population dynamics* Authors: Sophia N. Lyon, Joseph A. Tomoleoni, Julie L. Yee, Jessica A. Fujii, Nicole M. Thometz *Abstract*: Sea otters (*Enhydra lutris*) are vital keystone predators throughout the North Pacific that were nearly extirpated during the maritime fur trade. Recovery of southern sea otters (*E. l. nereis*) has proceeded slowly, with much of their historical range remaining unoccupied, resulting in reduced ecosystem functioning. Numerous studies have used foraging metrics to assess population status of southern sea otters throughout their current range, but little is known about the northern range extent, where a stall in expansion has limited recovery. Thus, we collected census and foraging data of sea otters at Año Nuevo State Park, California, from 2019–2021 to determine sea otter abundance, diet composition, diet diversity, and average energy intake rate at the northern range edge. We then assessed regional population status by comparing values from Año Nuevo with previously collected data from other locations in California, including high-density, range center sites and low-density, range periphery sites. We found that sea otter density at Año Nuevo was greater than surrounding areas at the northern range periphery and average energy intake (95% CI = 9.51 ± 0.91 kcal min-1) more closely resembled values observed at high-density sites. Further, dietary diversity (using Shannon-Wiener index) was intermediate between previously studied high- and low-density populations (H=1.81), with crabs making up the largest proportion of the diet (~56%). Overall, this study highlights possible effects of occupation time and range stagnation, identifies unique aspects of the prey resource base at Año Nuevo, and provides insight into the ongoing lack of northern range expansion. *Link to Article*: https://www.int-res.com/abstracts/esr/v54/p383-394/ Please reach out if you have any questions. Best, Nicole Thometz Associate Professor Department of Biology University of San Francisco -- Nicole M. Thometz, Ph.D. Associate Professor, Department of Biology University of San Francisco 2130 Fulton Street, San Francisco, CA 94117 Office: Harney 219H Website: https://thometzlab.wixsite.com/thometzlab