The at-sea behaviour of intermittently breeding adult female southern elephant seals from Marion Island

• Other Authors: De Bruyn, P.J. Nico, Tosh, Cheryl A., Van der Merwe, Caitlin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Pretoria 2023
• Subjects: UCTD; Zoology; Bathymetry; Net primary productivity; Southern elephant seals; Body condition; Diving behaviour; Intermittent breeding; Marion Island; Southern Ocean; Elephant Seals; Macquarie Island; Mirounga leonina; Southern Elephant Seals
• Online Access: https://repository.up.ac.za/handle/2263/89784; https://doi.org/10.25403/UPresearchdata.22140551.v1; https://doi.org/10.25403/UPresearchdata.22140551

Dissertation (MSc (Zoology))--University of Pretoria, 2023. Southern elephant seals (SES), Mirounga leonina, are large capital breeding marine predators that have a circumpolar distribution in the Southern Ocean. Female SES typically give birth to a single pup each year, however, recent studies from subantarctic Marion Island and Macquarie Island have identified adult female SES that skip reproductive events. Previous studies on intermittently breeding elephant seals focused on theoretical reasons for this behaviour using demographic data. Few studies have empirically analysed the at-sea behaviour of female SES when they skip a breeding event, and how this behaviour may relate to body mass and environmental conditions. This dissertation focuses on the at-sea behaviour of intermittently breeding adult female SES from Marion Island and how this behaviour may be described relative to their foraging patterns, body condition and environmental variables. Capital breeders need to acquire sufficient energy prior to breeding to support maternal maintenance and lactation costs. Variation in maternal body mass depends on environmental conditions and individual heterogeneity in foraging ability. Females should allocate more energy to their offspring when environmental conditions create profitable foraging potential and should prioritise their own survival in sub-optimal foraging years. Body mass is a proxy for body condition, and intermittent breeding may be an adaptive reproductive trajectory where females in sub-optimal condition skip breeding for a year and spend more time foraging to improve their energy reserves. This has the potential to increase maternal and offspring fitness compared to continually breeding females that may breed in sub-optimal condition. Three multiparous female reproductive skippers were identified from the Marion Island SES breeding population that were repeatedly tracked during skipping and breeding years from 2007 and 2012 (GG335, n = 5 tracks; WW061, n = 3 tracks; YY039, n = 2 tracks). Each ...