Reproductive natural history of endangered Cook Inlet Beluga whales: insights from a long-term photo-identification study

Beluga whales ( Delphinapterus leucas ) occur broadly throughout the polar and subpolar regions of the Northern Hemisphere, and as a whole, the species is of low conservation concern. However, some populations, including Alaska’s Cook Inlet beluga whales (CIBW), are in decline for reasons that remain poorly understood. Currently, information on population-specific reproductive parameters of CIBW is non-existent. To address this data gap, we examined long-term photo-identification data of CIBW for insight into the reproductive natural history of this endangered subarctic population. Data are from 438 photo-ID surveys conducted 2005–2017 and over 400 identified individuals, augmented with data from strandings, biopsies, and tagging. During the April–October ice-free field season, we observed neonates July–October but never April-June. We photo-documented three suspected births during July–September. Neonates were present in 30% of groups and encountered and comprised 2% of all belugas observed. Over the course of the 13-year study, the number of calves seen with an individual mother ranged from 1 to 5, with inter-birth intervals ranging from 2 to 13 years. This corresponds to rates of 0.08–0.38 calves per year per mother. Known-aged mothers ranged in age from 13 to 31 years. Skin color was not a reliable indicator of sexual maturity. Calves photographed alongside their mothers were estimated to be 1–8 years old, although most were 1–4 years old. Some mothers (6%) were accompanied by a neonate and an older calf. These summaries of observational data provide critical insight into CIBW reproductive natural history that will inform future population modeling and management decision-making.