Arctic | Mammals
Age and length at sexual maturity and pregnancy rate of Bering-Chukchi-Beaufort Seas bowhead whales Presenter: Kayla Scheimreif , kayla.scheimreif@north-slope.org, North Slope Borough Craig George , jtundra@barrow.com, Department of Wildlife Management, North Slope Borough Geof Givens , geof@geofgivens.com, Givens Statistical Solutions Lara Horstmann , lahorstmann@alaska.edu, University of Alaska Fairbanks Robert Suydam , rssuydam@gmail.com, Department of Wildlife Management, North Slope Borough Raphaela Stimmelmayr , raphaela.stimmelmayr@north-slope.org, North Slope Borough, Department of Wildlife Management Gay Sheffield , ggsheffield@alaska.edu, University of Alaska Fairbanks Todd Sformo , todd.sformo@north-slope.org, North Slope Borough Dept. of Wildlife Management Brian Person , brian.person@north-slope.org, Department of Wildlife Management, North Slope Borough Andrew Von Duyke , Andrew.VonDuyke@north-slope.org, North Slope Borough Department of Wildlife Management Leandra Sousa , leandra.sousa@north-slope.org, North Slope Borough Dept. of Wildlife Management Raymond Tarpley , rjtarpley@gmail.com, Dept. of Veterinary Integrative Biosciences, College of Veterinary Medicine & Biomedical Sciences Data from the Bering-Chukchi-Beaufort Seas stock of bowhead whales ( Balaena mysticetus ), harvested during 1973- 2021 by aboriginal subsistence hunters, were used to estimate parameters related to sexual maturity and pregnancy. Sexual maturity was determined from the presence/absence of corpora in the ovaries, or a fetus (n=187 females). Using sampling bias-corrected logistic regression, length at sexual maturity (LSM) was estimated as 13.45 m, 95% CI [13.00, 13.76]. There was a statistically significant trend in LSM over time, declining from 14.25 m during 1976-1990 to 12.78 m during 2013-2019. A previously published sex-specific growth model was used to translate LSM estimates to age at sexual maturity (ASM) yielding estimated ASM of 23.5 years, 95% CI [20.4, 26.7]. Pregnancy rate was determined from mature females (n=125), and from a subset limited to certain autumn-caught whales (n=37) to reduce bias. The proportion of pregnant females (PR) was estimated as 0.46, 95% CI [0.36, 0.55] and 0.38, 95% CI [0.20, 0.51], respectively. Both estimated PRs are consistent with a 3-year calving interval, because the larger estimate includes two cohorts of pregnant whales harvested in spring, and bowhead whale gestation is longer than 12 months. These analyses represent the most conclusive empirical estimates of ASM, LSM, and PR for this stock from the largest available datasets to date.
Alaska Marine Science Symposium 2023 279
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