Multi-year progesterone profiles during pregnancy in baleen of humpback whales (Megaptera novaeangliae)

Carley L Lowe; Kathleen E Hunt; Matthew C Rogers; Janet L Neilson; Jooke Robbins; Christine M Gabriele; Suzie S Teerlink; Rosemary Seton; C Loren Buck

doi:10.1093/conphys/coab059

Multi-year progesterone profiles during pregnancy in baleen of humpback whales (Megaptera novaeangliae)

Conserv Physiol. 2021 Jul 28;9(1):coab059. doi: 10.1093/conphys/coab059. eCollection 2021.

Authors

Carley L Lowe¹, Kathleen E Hunt², Matthew C Rogers³, Janet L Neilson⁴, Jooke Robbins⁵, Christine M Gabriele⁴, Suzie S Teerlink⁶, Rosemary Seton⁷, C Loren Buck¹

Affiliations

¹ Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA.
² Department of Biology, George Mason University and Smithsonian-Mason School of Conservation, Front Royal, VA 22630, USA.
³ Alaska Fisheries Science Center Auke Bay Laboratories, NOAA, National Marine Fisheries Service, Juneau, AK 99801, USA.
⁴ Humpback Whale Monitoring Program, Glacier Bay National Park and Preserve, Gustavus, AK 99826, USA.
⁵ Center for Coastal Studies, Provincetown, MA 02657, USA.
⁶ Alaska Regional Office, NOAA Fisheries, Juneau, AK 99801, USA.
⁷ College of the Atlantic, Bar Harbor, ME 04609, USA.

Abstract

Understanding calving rates of wild whale populations is critically important for management and conservation. Reproduction of humpback whales (Megaptera novaeangliae) is difficult to monitor and, even with long-term sighting studies, basic physiological information such as pregnancy rates and calving intervals remain poorly understood in many populations. We hypothesized that pregnant whales have sustained elevations in baleen progesterone that temporally correlate with gestation. To test this hypothesis, baleen progesterone profiles from two adult female North Pacific humpbacks, both with extensive sighting records and documented pregnancies, were compared to those of a nulliparous female (adult female never seen with a calf) and a juvenile male. Baleen specimens recovered during necropsy were subsampled every 2 cm from the base to the tip of the plate, with each interval representing 30-45 days of growth. Homogenized baleen powder was assayed for progesterone using enzyme immunoassays. The date of growth of each sampling location on the baleen plate was estimated based on stable isotope analysis of annual δ¹⁵N cycles. Progesterone profiles from both pregnant whales showed sustained high progesterone content (>350 ng/g) in areas corresponding to known pregnancies, inferred from calf sightings and post-mortem data. The younger female, estimated to be 13 years old, had higher progesterone during pregnancy than the 44.5 year old, but levels during non-pregnancy were similar. The nulliparous female and the male had low progesterone throughout their baleen plates. Baleen hormone analysis can determine how progesterone concentrations change throughout gestation and has potential for estimating age at first reproduction, pregnancy intervals, failed pregnancies and early calf mortality. Understanding rates of calving and current and historic reproductive patterns in humpbacks is vital to continuing conservation measures in this species.