Growth, maturity, reproduction, and life expectancy in ex-situ pacific walruses (Odobenus rosmarus divergens)

• Published in: BMC Zoology
• Main Authors: Todd Robeck, Etsuko Katsumata, Kazutoshi Arai, Gisele Montano, Todd Schmitt, Stacy DiRocco, Karen J. Steinman
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2022
• Subjects: Walrus; Reproduction; False pregnancy; Embryonic diapause; Gestation; Survivorship; Zoology; QL1-991; Arctic; Bering Sea; Pacific; Chukchi; Odobenus rosmarus; Sea ice; walrus*
• Online Access: https://doi.org/10.1186/s40850-022-00158-1; https://doaj.org/article/70cc796d97184f91aaef29edb512bf00

Abstract Background Pacific walruses are found in Arctic regions of the Chukchi and Bering Sea where rapid changes in environmental conditions resulting in loss of sea ice are occurring. Therefore, accurate life history data are crucial for species management plans and longitudinal data collected over the lives of individual walruses housed in zoos and aquaria provide otherwise difficult to obtain biological information. Results While similar at birth, Gompertz regression curves indicated that males grew faster than females (p < 0.0001) in weight (99 kg vs 57.6 kg/y) and length (26.9 cm vs 26.3 cm/y) with physical differences being detected by age 3 for weight and age 7 for length. Males reached adult weight at 13.5 ± 3.3 y and females by age 12.3 ± 2.3 y. The mean age at first ovulation and at first conception occurred at 8.8 y and 9.6 y. Greater than 75% of all conceptions and calving occurred between February and March and from May to June, respectively. Mean gestation lasted 423 d and false pregnancies lasted at least 169 d with a decrease (p < 0.05) in serum progesterone concentration between false pregnancy and pregnancy occurring within 6 months after ovulation. Based on these results, we estimated embryonic diapause to last from 120 to 139 days, and fetal growth last ~ 284 days. All males older than 8 y had an increase in serum testosterone and body weight that was highest in February and lowest in July. Overall, no differences were observed between male and female survival, with a mean (± SEM) life expectancy of 19.5 ± 1.5 y, respectively. Currently, the oldest male and female captive walruses are 40 and 43 y, respectively. Conclusions Data provided herein include details of life history characteristics of zoo and aquaria housed walruses that are useful for wild population recovery models. In particular, results on survivorship and the identification of the most vulnerable period for calf survival can help with model development and suggests that for recovery to occur birthing locations for this ...