Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximise reproduction and survival. In this study we use three reproductive performance measures; maternal expenditure, offspring weaning mass and first year survival to investigate the role maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island's southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n=29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn first year pup return rates (as a proxy for survival) were assessed through the intensive mark-recapture program.Pup survival increased with female age and weaning mass. Pups of young females aged 3 to 6 years have a lower 1 st year survival probability compared to pups of older and larger females.

Recruitment age plays a key role in life‐history evolution. Because individuals allocate limited resources among competing life‐history functions, theory predicts trade‐offs between current reproduction and future growth, survival and/or reproduction. Reproductive costs tend to vary with recruitment age, but may also be overridden by fixed individual differences leading to persistent demographic heterogeneity and positive covariation among demographic traits at the population level. We tested for evidence of intra‐ and inter‐generational trade‐offs and individual heterogeneity relating to age at first reproduction using three decades of detailed individual life‐history data of 6,439 capital breeding female southern elephant seals. Contrary to the predictions from trade‐off hypotheses, we found that recruitment at an early age was associated with higher population level survival and subsequent breeding probabilities. Nonetheless, a survival cost of first reproduction was evident at the population level, as first‐time breeders always had lower survival probabilities than prebreeders and experienced breeders of the same age. However, models accounting for hidden persistent demographic heterogeneity revealed that the trade‐off between first reproduction and survival was only expressed in “low quality” individuals, comprising 35% of the population. The short‐term somatic costs associated with breeding at an early age had no effect on the ability of females to allocate resources to offspring in the next breeding season. Our results provide strong evidence for individual heterogeneity in the life‐history trajectories of female elephant seals. By explicitly modeling hidden persistent demographic heterogeneity we show that individual heterogeneity governs the expression of trade‐offs with first reproduction in elephant seals.

The Marine Mammal Programme (MMP) conducts research on pinnipeds and killer whales at Marion Island, Prince Edward Islands, under the auspices of the Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria. The early history of the MMP is described, emphasizing the contributions in subsequent years, ending with current research. The setting up of long-term studies such as the mark-resighting of southern elephant seals Mirounga leonina was implemented in 1983. The varying fates of the three seal populations are described, with the Marion Island elephant seal population declining by 87% from 1951 to 2004, followed by a change in growth rate in 1997 and a current increase. Sympatric populations of Subantarctic fur seals Arctocephalus tropicalis and Antarctic fur seals A. gazella breed at Marion Island and the recovery (following cessation of commercial sealing) and subsequent rapid increase of these populations are documented. Insights into many aspects of elephant seal and fur seal biology, including life-history, demography, diet, growth, foraging and ranging behaviour are described.Ancillary work on morphology, genetics, anthropogenic influences and rare events are mentioned, as well as the extent of current research that addresses population dynamics in an ecosystem context, i.e. to relate survival, fecundity and foraging success to environmental conditions. Presently, the response of the populations to increased abundance is gauged and investigations into the foraging ecology, maternal provisioning and diet of both fur seal populations reflect changes in the environment. Opportunistic, land-based photographic identification of killer whales (Orcinus orca) provide baseline population size, seasonal abundance and sociality data for the Marion Island population. Recent dedicated observations are used to quantify observer effort, improve sighting rates and to further our understanding of the 3 potential impact of the killer whale population on resident pinniped populations. The MMP benefits from collaboration with leading national and international researchers. The programme has a long track record of training postgraduate students, as evidenced by the reference list to the manuscript. Their endeavours in the field and completion of postgraduate studies make them ideal candidates to contribute to marine mammal science in South Africa. October 1951-April 1952 published the first scientific papers on the seals of the island (Rand 1955(Rand , 1956(Rand , 1962, followed by Le Grange (1962) (Condy et al. 1978) was elaborated on in an opportunistic fashion (Keith et al. 2001). Throughout, personnel were also alert to seal vagrants (Kerley 1983a) or transients hauling out, sightings of cetaceans (Condy and Burger 1975, Ryan and Bester 2008, fur seal females successfully rearing twin pups Kerley 5 1983, de Bruyn et al. 2010) and extraordinary leucistic individuals (de Bruyn et al. 2007, Reisinger et al. 2009). Terrestrial feeding events by fur seals (Hofmeyr and Bester 1993, ...

Abstract:Physically weighing large marine mammals sequentially over time has presented researchers with a logistical challenge and has severely limited sample sizes. Using a well-established photogrammetry method we developed a simple mathematical method to calculate accurate mass measurements at specific stages in the life cycle of a top marine predator. Female southern elephant seals (n 5 23) at Marion Island were sampled sequentially using photogrammetry and three-dimensional models (based on each photogrammetry project) were built for estimation of body mass. Simple equations were applied to obtain mass at critical instances in their life cycle. Marion Island elephant seal mass data was compared to data obtained from physically weighed elephant seals from King George, South Georgia and Macquarie islands. Females from Marion Island are smaller, but their percentage lactation mass loss is similar to females from these other populations. The similarity of percentage mass loss during lactation between different female populations illustrates the accuracy and practicality of the photogrammetric method over a temporal scale. Photogrammetric mass estimation can be used alongside datasets of physically weighed animals and can greatly benefit ecology and life history studies.

Assessing body mass in mammals is of importance as it influences virtually all aspects of mammal physiology, behavior and ecological parameters. However, the assessment of body mass of large mammals is potentially dangerous and logistically challenging. Photogrammetry (measurements through the use of photographs) is a well‐established science. In zoology it has been used with varying success to estimate the size and mass of some marine and terrestrial mammal species. However, photogrammetric body mass estimation of terrestrial mammals has received comparatively little attention. This is largely due to species' variable morphological attributes which complicates measurement especially if, for 3D orientation, photogrammetric models are dependent on identifiable features on the animals themselves. Ninety‐two individuals belonging to 16 terrestrial mammalian species were weighed and photographed for body mass estimation using a volumetric photogrammetry method, purposely applied with commercially available software. This method is not dependent on identifiable body features for 3D orientation. Measured body mass ranged from 25 kg to 4060 kg. Photogrammetric mass estimates versus physically weighed mass was plotted and the goodness of fit assessed for each species. Body size, shape and physiological attributes influence the accuracy of body mass estimation between species (although consistent within species), largely attributed to morphological features (e.g., hair length and posture). This photogrammetric method accurately estimated the body mass of several terrestrial mammal species. It represents innovative use of photographs to create calibrated three‐dimensional imagery for accurate quantification of mammalian metrics, specifically body volume and mass. Advances of a method that is not subject to species, sex or age is advantageous and suitable for wide application in our effort to model population demography.