Dear Colleagues, On behalf of lead author Shannon Atkinson and co-authors Trevor Branch, Adam Pack, Jan Straley, Jon Moran, Chris Gabriele, Kendall Mashburn, Kelly Cates and Suzanne Yin, I am pleased to inform you about our new paper " Pregnancy rate and reproductive hormones in humpback whale blubber: Dominant form of progesterone differs during pregnancy " published in the journal General and Comparative Endocrinology. Below, please find the full citation for the article and the abstract. Our findings are based on biopsy sampling data collected from 2004-2006 in Hawai’i and Alaska. If you would like to receive a pdf of this paper, please contact us. Wishing everyone in our community a happy, healthy, and peaceful holiday season. Mahalo, Adam Atkinson, S., Branch, T. A., Pack, A .A., Straley, J. M., Moran, J. Gabriele, C., Mashburn, K. L., Cates, K. & Yin, S. (2022). Pregnancy rate and reproductive hormones in humpback whale blubber: Dominant form of progesterone differs during pregnancy. General and Comparative Endocrinology. 114151. https://doi.org/10.1016/j.ygcen.2022.114151 Abstract To better understand reproductive physiology of humpback whales *Megaptera novaeangliae *that reside in Hawai’i and Alaska, enzyme immunoassays were validated for both progesterone and testosterone in free-ranging and stranded animals (n = 185 biopsies). Concentrations were analyzed between different depths of large segments of blubber taken from skin to muscle layers of stranded female (n = 2, 1 pregnant, 1 non-pregnant) and male (n = 1) whales. Additionally, progesterone metabolites were identified between pregnant (n = 1) and non-pregnant (n = 3) females using high pressure liquid chromatography (HPLC). Progesterone concentrations were compared between juvenile (i.e., sexually immature), lactating, and pregnant females, and male whales, and pregnancy rates of sexually mature females were calculated. Based on replicate samples from ship struck animals collected at 7 depth locations, blubber containing the highest concentration of progesterone was located 1 cm below the skin for females, and the highest concentration of testosterone was in the skin layer of one male whale. HPLC of blubber samples of pregnant and non-pregnant females contain different immunoreactive progesterone metabolites, with the non-pregnant female eluate comprised of a more polar, and possibly conjugated, form of progesterone than the pregnant female. In females, concentrations of progesterone were highest in the blubber of pregnant (n = 28, 28.6 ± 6.9 ng/g), followed by lactating (n = 16, 0.9 ± 0.1 ng/g), and female juvenile (n = 5, 1.0 ± 0.2 ng/g) whales. Progesterone concentrations in male (n = 24, 0.6 ng/g ± 0.1 ng/g) tissues were the lowest of all groups, and not different from lactating or juvenile females. Estimated summer season pregnancy rate among sexually mature females from the Hawai’i stock of humpback whales was 0.562 (95 % confidence interval 0.528–0.605). For lactating females, the year-round pregnancy rate was 0.243 (0.09–0.59), and varies depending on the threshold of progesterone assumed for pregnancy in the range between 3.1 and 28.5 ng/g. Our results demonstrate the synergistic value added when combining immunoreactive assays, HPLC, and long-term sighting histories to further knowledge of humpback whale reproductive physiology. -- Adam A. Pack, Ph.D. Professor and Chair (Psychology) Departments of Psychology and Biology University of Hawai'i at Hilo 200 West Kawili Street Hilo, Hawai'i 96720 (Office Voice): 808-932-7082 (Email): pack@hawaii.edu (Faculty Webpage): https://hilo.hawaii.edu/faculty/adam-a-pack/ (UH Hilo Lab): https://hilo.hawaii.edu/faculty/adam-a-pack/marine-mammal-lab/ (Non-profit organization): https://thedolphininstitute.org/ Recent PBS Documentary Films: Humpback Health: https://www.youtube.com/watch?v=s0_pvMeGVho Mystery of the Humpback Whale Song: https://www.youtube.com/watch?v=HgEQ0TUjZh0 "Do or do not; there is no try." Yoda