Analysis of the condition of female (body fat and protein composition, weight and diet) Weddell seals (Leptonychotes weddellii) and the implication for reproductive success

Weddell seals lay down substantial fat deposits during the non-breeding season and then expend the stored energy during an intensive lactation period. Fluctuations in energy acquisition prior to breeding are expressed as variations in maternal mass and condition at parturition. Failure to locate sufficient food prior to parturition will result in poor reproductive success. The link between variations in energy aquisition (affected by environmental conditions) and maternal condition on lactating behaviour, pup condition and survivorship was examined by monitoring the Weddell seal colony at Hutton Cliffs, Erebus Bay during the breeding season. Females and their pups were captured post partum, during mid-lactation and at the end of the lactation period and weighed. Deuterium and tritium dilution techniques as well as ultrasonic techniques were used to assess the condition (total amount of fat possessed) of females to determine the relative change in body composition (i.e. fat and protein) over time and the growth of the pup. The over winter diet of the females was determined by taking a blubber sample and analysing it for fatty acid composition, lipid use and transfer during lactation. Fresh scat samples were also collected from around the colony for the entire field season and prey remains were identified. Because identification is sometimes difficult, a DNA based method was used to identify species of prey remains. Blood and milk samples were also collected at the beginning, mid and end of lactation and examined to determine the ontogeny of disease resistance in pups.