Breeding and Calving Seasonality in the Endangered Cook Inlet Beluga Whale Population: Application of Captive Fetal Growth Curves to Fetuses and Newborns in the Wild

September 29, 2019

This paper presents results from the youngest portion of this population, deceased fetuses and calves-of-the-year, to provide insights into breeding and calving seasonality for this endangered population.

Fetuses were collected from 10 deceased CIB females (Table 1, Figure 1). During the necropsy examination, another seven deceased adult females were found to be lactating (postpartum) or resting (not pregnant, a few ovulating) (Shelden et al., 2019). Four neonates (with fetal folds still present) and 14 calves-of-the-year were also examined (Table 1, Figure 1). Calves were assumed to have been born within the year they stranded based on length (<~180 cm straight length [SL] from rostrum to fluke notch, e.g., Hill, 2009), and, when possible, by examining any teeth in the mandible for the presence of prenatal lines or growth layer groups (Vos et al., 2019; also see Table S1 for examples of older calves). Per Robeck, Schmitt, and Osborn (2015), a fetus was classified as early stage (0–156 days in utero) if smaller than 50 cm in length from rostrum to fluke notch, mid-stage (157–313 days in utero) from 50 cm to 70 cm, and late-stage when >70 cm (314–470 days in utero). Of the 10 females with a fetus (Table 1), two had early stage fetuses, two had mid-stage, and six had fetuses that were approaching near-term (all >90 cm in length).


Shelden, K. E. W. ; Robeck, T. R. ; Goertz, C. E. C. ; McGuire, T. L. ; Burek-Huntington, K. A. ; Vos, D. J. ; Mahoney, B. A.; DOI:, Marine Mammal Science

Last updated by Alaska Regional Office on 06/05/2020

Cook Inlet Beluga Whale Cook Inlet Beluga Whale Research