Life history studies of the southern elephant seal population at Marion Island

• Main Author: De Bruyn, P.J. Nico
• Other Authors: Bester, Marthan Nieuwoudt
• Format: Thesis
• Language: unknown
• Published: University of Pretoria 2013
• Subjects: Methodology advancement; Population demography; Longevity; Senescence; Survivorship; Tagging; Mark-recapture; Photogrammetry; Phocids; Southern ocean; Mirounga leonina; Experimental design; Ecosystem approach research; UCTD; Southern Ocean; Elephant Seal; Elephant Seals; Marion Island; Southern Elephant Seal; Southern Elephant Seals
• Online Access: http://hdl.handle.net/2263/28933; http://upetd.up.ac.za/thesis/available/etd-10222009-124552/

Holistic studies of mammalian life history factors and their consequences on population demography require an intensive, multifaceted field methodology and effort over long temporal scales. A 25-year longitudinal mark-recapture experiment on southern elephant seals, Mirounga leonina, at Subantarctic Marion Island provide such a foundation for demographic analyses and relevant methodology advancement. Two gaps in the methodology related to life history and population demographic research are, the absence of large samples of known mass individuals, and an inability to identify mother-pup relatedness. A novel three-dimensional photogrammetric technique is designed here that allows for mass estimation of large samples of southern elephant seals in the field. An effective temporary marking technique for unweaned pups is implemented that allows for identification of large samples of pups with known mothers prior to the maternal bond being severed at weaning. These known pups can then be marked with more robust tags and relatedness information is preserved long-term. Thus, mass estimates can now be applied as covariates in modelling analyses to address questions of, for example, maternal investment, kinship associated behaviour, and the consequences thereof on survival and reproductive parameters. The state change in the Marion Island southern elephant seal population from decrease to stabilisation/increase is shown to have resulted from improved survivorship in both juvenile and adult female age classes. Male seals of all ages did not indicate improved survivorship following the period of decline. The inflexion in survivorship is identified as 1994, whence improved survivorship of juvenile seals preceded that of young adult females. This inflexion in survivorship is postulated to have resulted in a population trend inflexion around 1998. Female southern elephant seals do not show evidence of actuarial senescence, but reproductive senescence is apparent after 12 years of age. A longterm reproductive cost (reduced ...