Effect of sex and ontogeny on the trophic ecology of Southern Ocean fur seals

• Main Author: Pretorius, Liezl Eleanore
• Other Authors: Bester, Marthan Nieuwoudt, Hofmeyr, G.J.G., Connan, M.A.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Pretoria 2021
• Subjects: UCTD; Antarctic; Southern Ocean; Antarc*; Antarctic Fur Seals; Arctocephalus gazella
• Online Access: http://hdl.handle.net/2263/78273

The biology of apex predators provides a valuable means of monitoring changes within the Southern Ocean. Knowledge of these animals is often incomplete as relatively little is known about the ecological roles of many marine predators within these ecosystems. They inhabit remote and poorly accessible habitats, making research difficult or nearly impossible. Two partially sympatric species of fur seals, Antarctic fur seals Arctocephalus gazella (AFS) and Sub-Antarctic fur seals A. tropicalis (SAFS), inhabit the Southern Ocean. Substantial differences exist in morphology and life history between the sexes of both species. Information on the influence of intrinsic factors such as sex, ontogeny and individual variation on their trophic ecology and their role as apex predators is limited. Certain parts of the populations (mostly adult breeding females) are more intensively studied than others, i.e., juveniles, sub-adults, adult males and non-breeding females. This study attempts to better understand the intra- and interspecific variation in the trophic ecology of Southern Ocean fur seals. After death, the teeth of an animal provide a record of its life history. Species, sex and age class are necessary for it to be scientifically useful and we show that external morphological features of upper canine teeth can deliver this information. Upper canine teeth can be used to age AFS and SAFS. External annular ridge counts provide a quick and approximate age estimate, but need confirmation by internal dentinal growth layer group counts. Seven external upper canine tooth measurements are used to determine sex within species and to distinguish between the two species. The seven upper canine tooth measurements considered in this study are easily repeatable and could be used in other species as well. The island of origin cannot be determined, possibly due to the small sample sizes. This method provides for the use of upper canine teeth in determining age, sex and species for specimens of unknown provenance. Fine-scale dentine ...