Hello MARMAM Members, On behalf of my colleagues and myself, I am pleased to share with you all our new research note “Reproductive and stress‐related hormones in whiskers from two North Pacific phocids: Harbor and ringed seals”, now available in early view at Marine Mammal Science. The article can be found here: https://bit.ly/38mVbJT. Keogh MJ, Charapata P, Karpovich S, Jones A, Sprowls C, Marshall CD. Reproductive and stress-related hormones in whiskers from two North Pacific phocids: Harbor and ringed seals. Mar Mam Sci. 2020;1–12. https://doi.org/10.1111/mms.12709 Summary Several populations of North Pacific pinnipeds are currently listed as depleted under the Marine Mammal Protection Act, endangered under the Endangered Species Act, of the United States or with unknown status, highlighting the need for new methods to assess the reproductive rates of these populations. Most phocids are annual breeders with estrus and parturition occurring on terrestrial or ice platforms. In phocids, serum progesterone concentrations remain elevated during late gestation, supporting identification of pregnancy after implantation (Gardiner, Boyd, Follett, Racey, & Reijnders, 1999; Gardiner, Boyd, Racey, Reijnders, & Thompson, 1996; Mellish & Iverson, 2005; Reijnders 1990). However, current sampling methods based on blood and feces only provide a snapshot of reproductive status. Recently, methods were developed to measure cortisol in whiskers (Karpovich, Skinner, Kapronczai, Smith, & Janz, 2019), highlighting the potential to measure reproductive hormones in whiskers from free-ranging phocid seals. Unlike other tissues currently used for determining reproductive status, whiskers do not require special storage or handling, which can be challenging in remote field conditions. More importantly, the potential to use whiskers to measure reproductive hormones may alleviate problems associated with a single sample by capturing reproductive hormone concentrations sequentially along the length of the whisker, allowing for the examination of hormone con- centrations over the course of one year for phocids (Greaves, Hammill, & Eddington, 2004; Hirons, Shell, & St. Aubin, 2001; Lübcker, Condit, Beltran, Bruyn, & Bester, 2016; Zhao & Schell, 2004). Given the potential utility of measuring reproductive hormones in phocid whiskers, our objectives were to (1) validate enzyme immunoassays (EIA) to measure reproductive and stress-related steroid hormones in phocid whiskers, (2) compare the patterns of multiple steroid hormones along the length of whiskers to evaluate the retention of steroid hormones in phocid whiskers, (3) apply immunohistochemistry (IHC) methods to explore deposition of progesterone and cortisol along harbor seal whiskers, and (4) investigate the influence of age class (i.e., adult vs. subadult) and reproductive state on hormone concentrations in whiskers. In this study, we report a novel method to measure reproductive hormones in phocid whiskers, providing another tool for future studies. We found hormones are deposited throughout the length of a phocid whisker, helping to validate the utility of whiskers as a reliable matrix for measuring reproductive hormones. We found differences in whisker progesterone concentrations between adults and subadults from two phocid species and between pregnant and nonpregnant adult harbor seals. There may be other reproductive steroid hormones, such as testosterone, that may also be useful for assessing age class. The timing of the whisker collection for both phocid species may influence detection of the rise in progesterone in the whisker likely associated with active gestation. Nevertheless, phocid whiskers contain hormones incorporated during the estimated years' worth of growth (Beltran et al., 2015, Hirons et al., 2001, Lübcker et al., 2016). Analysis of hormone concentrations from whiskers could be beneficial in accruing long-term physiological data from keratinized tissues in phocids. Further, whiskers in archived collections from museums, stranding networks, and gov- ernment agencies could serve as a reservoir of samples to perform retrospective studies on phocid reproductive and stress physiology, helping to understand how future environmental changes may impact phocid physiology. Please email lead and corresponding author (Mandy Keogh, mandyjkeogh@gmail.com<mailto:mandyjkeogh@gmail.com>) if you have any questions or are interested in the manuscript. I would be happy to provide a PDF of the manuscript upon request (Patrick_charapata1@baylor.edu<mailto:Patrick_charapata1@baylor.edu>). Cheers, Patrick Charapata PhD Candidate, Baylor University Patrick_charapata1@baylor.edu<mailto:Patrick_charapata1@baylor.edu>